Future Landscape of Structural Materials in India 9789811685224, 9789811685231

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Debashish Bhattacharjee Shantanu Chakrabarti   Editors

Future Landscape of Structural Materials in India

Future Landscape of Structural Materials in India

Debashish Bhattacharjee · Shantanu Chakrabarti Editors

Future Landscape of Structural Materials in India

Editors Debashish Bhattacharjee Technology & New Materials Business Tata Steel Kolkata, West Bengal, India

Shantanu Chakrabarti Research Application Tata Steel Jamshedpur, India Indian Institute of Technology Kharagpur, India

ISBN 978-981-16-8522-4 ISBN 978-981-16-8523-1 (eBook) https://doi.org/10.1007/978-981-16-8523-1 © Indian National Academy of Engineering 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Foreword

Materials provide the backbone of all hardware. Success and efficiency of an engineering machine or system is as much dependent on the design as on the performance of the material that is used to fabricate the key components. Advancement in engineering, hence, significantly depends on development of engineering materials that can adequately meet the challenges posed by design, service conditions and unavoidable damage or degradation. Thus, the ambition of the nation to be atma nirbhar (self-reliant) will substantially depend on our ability to design, develop and integrate advanced materials and allied manufacturing systems that will not only match the international specifications, but will also provide an advantage for engineering the future of the nation. Indian National Academy of Engineering (INAE), mandated to promote excellence in engineering profession and policies, constitutes engineering forum on specific topics or themes both of contemporary relevance and futuristic ambition. It is with this intention, the INAE Forum on Indian Landscape of Advanced Structural Materials was created to review the current status of availability, quality and adequacy of structural (load bearing) materials in India and outline the gap and challenges to be overcome to meet the current and futuristic demands in construction, strategic, aerospace, automobile, energy and all other important sectors. Obviously challenges lie not just in raw material, equipment and competence, but also in creation of demand and sustenance of interest and business. Therefore, the task is neither easy nor trivial, but is absolutely essential if India truly means to be atma nirbhar. I am glad that the INAE Forum on Indian Landscape of Advanced Structural Materials is now ready to publish a special volume with very well researched articles addressing specific thematic areas authored by the most eminent engineers and technologists of the country. I sincerely hope that this effort and the articles will provide a ready reference to the planners, researchers, entrepreneurs and industry-leaders both from civilian and strategic sectors in the country for developing advanced structural materials encompassing metals and alloys, ceramics, polymers,

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Foreword

composites and hybrids that will make India both self-reliant and technologically advanced. Jai Hind! Indranil Manna Vice-Chancellor Birla Institute of Technology (BIT) Mesra, Ranchi, Jharkhand, India

Preface

Conceived in 2016, this book has taken six years to evolve to the present shape. Along the way, three symposia were held on the subject. Writing the content involved painstaking efforts by the eminent authors to paint the current picture, compare with the best in the world and identify the gap areas for our nation to work on. The papers went through a rigorous refereeing process by subject matter experts across the globe. The objective was to create a document that focuses on structural materials and records the landscape of manufacturing competence, research and development capability in India and compares with global benchmarks. The idea was to identify the gaps and set direction for national level actions to take India to world leadership and self-reliance. Structural materials are core to building a self-reliant nation. Metals such as steel, aluminium and titanium, non-metals such as polymers, polymer-matrix composites, ceramics, glass, cement and concrete make the infrastructure on which a nation runs, produces energy, defends its borders and fuels its industrial growth. Materials, of themselves, affect us little; it is the way we use them which influences our lives, said Epictetus in AD 50-100, in his Discourses Book 2, Chapter 5. This book covers most of the major structural materials and their applications in energy, construction, defence and other large sectors. It is hoped that this book will be relevant to multiple sections of readers. The student may find this a useful source of information about structural materials and their use; the professor perhaps will find areas in which research can be initiated; the policy-maker may find this book useful to focus into areas that need institutional attention and funding.

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As our nation makes rapid progress, the content of such a book will need to be updated. It is hoped that a next edition of this book will make the content relevant to the period and add other sectors important for the nation that are missed out in this edition. The editors wish everyone a pleasant read. Dr. Debashish Bhattacharjee Vice President Technology & New Materials Business Tata Steel Kolkata, India Dr. Shantanu Chakrabarti Visiting Scientist, DMSRDE (DRDO) Ex-Head, Research Application Tata Steel Jamshedpur, India Formerly INAE Distinguished Visiting Professor Indian Institute of Technology Kharagpur, India

Contents

Steel as a Structural Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basudev Bhattacharya and Debashish Bhattacharjee

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Aluminium As a Structural Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saikat Adhikari, Vilas Tathavadkar, and Biswajit Basu

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Titanium and Magnesium as Structural Materials . . . . . . . . . . . . . . . . . . . . Amol A. Gokhale

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Structural Materials in Nuclear Energy Sector . . . . . . . . . . . . . . . . . . . . . . . G. K. Dey

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Advanced High-Temperature Structural Materials in Petrochemical, Metallurgical, Power, and Aerospace Sectors—An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pradyut Sengupta and Indranil Manna

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Structural Biomaterials for Affordable Health Care . . . . . . . . . . . . . . . . . . 133 Bikramjit Basu, Surya R. Kalidindi, Nandita Keshavan, and Kingshuk Poddar FRP Composites: A Prospective Structural Material for the Indian Landscape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Rajesh Kumar Prusty and Bankim Chandra Ray Present Status and Future Indian Perspectives of Advanced Fibre-Reinforced Composites for Structural Applications . . . . . . . . . . . . . 187 N. Eswara Prasad, Debmalya Roy, Suresh Kumar, and Dibyendu S Bag Structural and Functional Properties of Architectural Glass . . . . . . . . . . . 211 Himadri Sekhar Maiti The Status of Bulk Metallic Glass and High Entropy Alloys Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 S. R. Reddy, P. P. Bhattacharjee, and B. S. Murty

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Refractories as Advanced Structural Materials for High Temperature Processing Industries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Arup Ghosh, Somnath Sinhamahapatra, and Himansu Sekhar Tripathi Use and Prospects of Concrete as a Cementitious Material . . . . . . . . . . . . 293 Sriman K. Bhattacharyya and Arghya Deb Advanced Techniques for Characterization of Structure, Composition and Mechanical Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 Rahul Mitra

About the Editors

Dr. Debashish Bhattacharjee completed Ph.D. in Materials Science & Metallurgy from the University of Cambridge, UK, in 1993. He joined Tata Steel R&D in 1996 and headed the R&D function as Chief Research & Development and Scientific Services between 2002 and 2009. In 2009, he was seconded to Tata Steel Europe, based in the Netherlands, as Group Director Research, Development & Technology for the Tata Steel Group. Dr. Bhattacharjee’s expertise lies in the development of materials and associated technologies. He leads steel-related technology development in Carbon Capture and Usage, Generation of cheap, green Hydrogen, Utilisation of low grade Raw Materials and Materials for Mobility of the Future. He is also responsible for setting up new businesses in materials beyond steel—in Composites, Graphene and Medical Materials. He has more than 50 international peer-reviewed journal publications and 20 patents. He is a Fellow of the Indian National Academy of Engineering and the Indian Institute of Metals (IIM). He received the Metallurgist of the Year Award by Govt of India in 2004 and IIM Tata Gold Medal in 2021. He has been a Visiting Professor at the Imperial College London, University of Warwick, and the University of Science and Technology, Beijing, China. Currently, he is Vice President, Technology & New Materials Business, Tata Steel, based in Kolkata. Dr. Shantanu Chakrabarti graduated in Mechanical Engineering from Jadavpur University in 1972 and got his M.Sc. and Ph.D. (1983) in Applied Energy from Cranfield University, UK. On return to India, he worked in Wellman Incandescent India Ltd in their Furnace division before joining Tata Steel in 1989, where he worked in the Energy & Economy department and Cold Rolling Mill, retiring finally in 2011, as Head, Research Applications, R&D. He was the winner of the International Innovista prize in 2009, as part of a team, for a project on Nano-fluid cooling. He was also an INAE Distinguished Visiting Professor at IIT Kharagpur (2011–2016) and also a member of the Academic Review Committee for IIT, Kanpur in 2014. Dr. Chakrabarti served as the Technical Editor of the volume Metals & Materials as a

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About the Editors

part of the VISION 2035 document (2016) published by the DST. He also edited the volume, Evolution of Technology at Tata Steel: A 50 year Narrative (2017). Currently he is an honorary Visiting Scientist at DRDO, in their DMSRDE unit at Kanpur.

Steel as a Structural Material Basudev Bhattacharya and Debashish Bhattacharjee

1 Introduction The modern civilization cannot be imagined without steel. The application of steel can be seen everywhere and in every part of human life. Some of its unique qualities are (a) high strength and toughness with simple and lean compositions, (b) different grades and properties for different applications, (c) different properties and microstructures can be created just by applying different heat treatments with the same steel composition, (d) most inexpensive among all the structural materials, (e) steel is 100% recyclable, etc. Since its earliest known production in 1800 BC [1, 2], steel has always been the most versatile material for the fabrication of numerous types of articles. There is no material, other than steel, which can be considered for the wide range of structural applications like building construction to ship manufacturing. The infrastructure development of any country in the world is closely associated with the development and application of various structural steel grades. Therefore, steel is undoubtedly the best and most widely used material for various structural applications. In the fast-changing world of materials science and engineering, different kinds of materials are now also being developed as structural materials, such as aluminium and magnesium alloys, ceramics, composites, polymers. In some areas, these can even replace steel to some extent. A simple example is the application of fibres and plastics in car bumpers, or the use of aluminium alloys in manufacturing automobile body panels in some relatively expensive cars, which serves the purpose, as well as reduces the vehicle weight. However, it is still difficult to conceptualise a replacement B. Bhattacharya Research and Development, Tata Steel, Jamshedpur, India D. Bhattacharjee (B) Technology & New Materials Business, Tata Steel, Kolkata, India e-mail: [email protected] Forum on Indian Landscape for Structural Materials, INAE, New Delhi, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_1

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of structural steels in construction of a bridge, or a building, or a container ship. So, steel has its own importance, which is going to continue for many more years. The present article is an attempt to briefly understand the prospect of some prominent fields of infrastructure development in India in the coming years, the potential of usage of structural steel in those areas, and the areas of technological research and development to meet those requirements.

2 Industrial Capability of Steel Production—Indian Scenario The steel consumption per capita is often considered a yardstick of overall development of any country. Over the past few years, this figure for India has increased from 58.8 kg in 2014 to about 72.8 kg in 2019 [3]. However, it is still way below the world average value of 224.5 kg in 2018–19 [4]. For China, the figure is 590 kg. A look at the trend of crude steel production in the world for the period 1950–2018 reveals a ninefold increase in about last 70 years, as shown in Fig. 1 [5]. In 2018, China topped the list with 928.3 million tonnes (Mt), followed by European Union with 168.2 Mt. India, for the first time, superceded Japan, with a production figure of 106.5 Mt [6], while Japan slipped to the third position with a production figure of 104.3 Mt. In 2019, India held the position of second-largest producer of crude steel (as a single country) [7] with a production figure of 111.2 Mt. Figure 2 [5] compares the figures between 2009 and 2019, showing that China continues to dominate by massive margins in production as well as in usage of steel.

1800

Average growth rates % per annum

1600 Crude steel producon, million tonnes

Fig. 1 Crude steel production in the world [5] (Courtesy of World Steel Association)

1400 1200 1000 800

Years

World

1950-55 1955-60 1960-65 1965-70 1970-75 1975-80 1980-85 1985-90 1990-95 1995-00 2000-05 2005-10 2010-15 2015-18

7.4 5.1 5.6 5.5 1.6 2.2 0.1 1.4 -0.5 2.5 6.2 4.5 2.5 3.7

600 400 200

0 1950

1960

1970

1980 1990 Year

2000

2010

Steel as a Structural Material

3

53.3%

Crude steel producon

46.6%

2009: 1239 Mt

2019: 1869 Mt

11.3% 8.5%

7.1% 6.8% 7.3% 6.3% 5.8% 5.3% 5.1% 6.0%

7.9%

5.4% 6.7% 6.4%

2.3% 2.1%

China

India

Japan

Other Asia Others

Other Europe

CIS

NAFTA

Finished steel products

51.3% 47.8%

2009: 1153 Mt

9.3% 9.9% 10.3% 5.0% 5.7% 4.6% 3.6%

China

EU

India

Japan

10.5% 7.6%

2019: 1767 Mt

9.0%

7.3% 7.6% 2.0% 1.9% 3.2% 3.3%

Other Asia Others

EU

Other

CIS

NAFTA

Fig. 2 Steel production and use: geographical distribution [5] (Data: Courtesy of World Steel Association)

3 Trends and Drivers—Some Important Sectors of Structural Steels The huge amount of usage of steel, that spans over different segments of structural applications, boosts the infrastructure development. An attempt is made in the following sub-sections to understand the present scenario vis-à-vis the prospect of steel usage in India. A few prominent sectors, such as construction, transport, clean energy and mobility, are discussed here.

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3.1 Infrastructure—Construction and Transport Transport and Utility are the two most important segments among infrastructure development: • Transport networks: Steel is required for bridges, tunnels, rail tracks and in constructing buildings such as fuelling stations, railway stations, ports and airports. About 60% of steel used in these applications is as rebar and the rest is in the form of sections, plates and rail track. • Utilities (fuel, water, power): Over 50% of the steel used for this application is in underground pipelines to distribute water to and from housing, and to distribute gas. The rest is mainly rebar for power stations and pumping houses. 3.1.1

The Current Situation

Currently, the construction sector alone accounts for more than 50% of world steel demand [8]. In India also, the infrastructure sector significantly contributes to the economic growth of country. Nearly 9% of the GDP of India is spent on infrastructure development [9]. As per economic survey of 2017–18, the infrastructure market revenue in India is expected to rise to a figure of more than 2500 billion US$, as compared to a value of 1365 billion US$ in 2015, (See Fig. 3). Similarly, the Indian real estate market is also expected to rise from 126 billion US$ in 2015 to about 180 billion US$ (See Fig. 4). The construction industry in India, in general, includes all sub-sectors, such as roads and highways, construction equipment, urban infrastructure, railways and metro rail projects, dedicated freight corridors, industrial corridors, real estate and power sector. As far as road construction is concerned in India, there is a tremendous prospect of growth. This industry experienced a growth of 2.9% during 2011–15. In next 5 years, the growth was expected to be around 5.6%. After continuing an impressive growth rate for a few years [10], there was an abrupt downfall during 2019, which may be connected to the global economic turmoil. However, a few Fig. 3 Infrastructure market revenue in India, in US$ billion [9]

Infrastructure market revenue in India, US$ billion 2552.4

1365.6

2015

2021

Steel as a Structural Material

5

Fig. 4 Real estate market growth in India, in US$ billion [9]

Real estate market growth in India, US$ billion 180

126

2015

2020E

sectors such as urban infrastructure, railways, oil and gas which contribute significantly to the infrastructure segment have not been affected so badly. Figure 5 [7] shows the growth of highway construction in India. Building construction is an important part of the entire construction sector. Steel is readily available, affordable and safe. Its strength, versatility, durability and 100% recyclability allow for improved environmental performance across the entire life cycle of buildings. Various fabrication steps during the construction of a building, and the subsequent operation of a building, which involves direct consumption of fuel and electricity, lead to substantial CO2 emission throughout its life cycle. The buildings, in general, account for about 28% of global CO2 emission [11]. It is believed that steel has an important role to play in making buildings with net zero operational carbon by 2050 [8], and there is ample opportunity of research for developing new energy-efficient building designs. For example, a near Zero Energy Building (nZEB)

Highway construcon in India (km) 10855 9829

8784

8231 6061 4260

4410

FY14

FY15

FY16

FY17

FY18

FY19

FY20*

Fig. 5 Highway construction in India in km (*Till February 2020) [7] (Data: Courtesy of India Brand Equity Foundation)

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has been designed by HAMK Sheet Metal Centre, Finland, bringing down the cost of electricity and heating to 6,100 US$ per annum from 14,600 US$ (reference building) [8]. The most common applications of steel in building construction are in structural sections, reinforcing bars (within concrete), sheet products (roofing, insulating panels, etc.), internal fixtures, fittings, rails, frames, stairs, etc. Railways is another important sector, which plays a vital role in the development of the entire country, and also from the point of view of usage of steel. Rail steel is a specific grade of steel, which is used for extension, replacement or doubling of railway tracks throughout the country. Apart from rail steel, other structural applications for steel include manufacturing of locomotives, coaches and wagons, construction of station buildings, railway bridges, tunnels, electric poles, etc. As of 2016–17, the total network length of Indian Railways was 121,407 km over a route length of 69,182 km [12].

3.1.2

The Growth Prospect in Medium Term (by Around 2025)

With high budget plans for the development of highways and smart cities, India is already a large market for infrastructure and construction activities, and it is expected to become the third-largest market in the world by 2025. The sustainable development would require investments of about Rs. 50 trillion by 2022 [9]. Government of India is also taking necessary initiatives to promote the construction sector. The vision of “House for All by 2022” is a part of that, for which 43,000 houses should be built every day, until 2022. The most important is that the fulfilment of all these plans will not be possible without using a huge quantity of steel, and therefore, the National Steel Policy (2017) focuses specifically on enhanced budgeting on infrastructure and construction through various government initiatives. India is also focussing on technologically advanced green/energy-efficient building [9]. It is important to understand that the advanced high-strength steels, which are normally considered mainly for automobile manufacturing, can also be used appropriately in construction industry, especially for the manufacturing of steel plates used in fabrication of various structures, such as offshore oil rigs, bridges, civil engineering and construction machines, rail carriages, tanks and pressure vessels, nuclear, thermal and hydroelectric plants.

3.1.3

The Growth Prospect in Long Term (by Around 2030)

A new UN report, published in 2019, indicates that the world population is going to be inflated by another 2 billion by 2050 [8]. The associated urbanisation, which is expected to be around 50% by 2050, would require steel for buildings and infrastructure. This real estate market is expected to grow to a figure of around one trillion USD by 2030, and contribute to about 13% of the GDP by 2025. The overall infrastructure segment is expected to contribute about 15% to Indian economy by 2030.

Steel as a Structural Material

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Airport Authority of India (AAI) now aims at constructing more than 20 airports in tier II and tier III cities in next 5 years, while more than 50 airports are required in India by 2030 [9], with an investment of 36–45 billion USD. In addition, the huge railway network of India, the fourth largest in the world, is expanding every year to reach the ever-increasing population and urbanisation. The developmental activities would need an investment worth Rs. 50 lakh crores by 2030 [7].

3.2 Clean Energy On one hand, there is an increasing demand for energy in all industrial segments. On the other hand, the increasing environmental pollution in past few decades has now taken the shape of a serious threat to earth and mankind. Therefore, in true sense, there is an increasing demand for clean energy. In the present scenario, natural gas has been identified as a major source of clean energy. Apart from that usage of unconventional energy sources, such as solar power and wind energy, is also expected to rise significantly in the coming years [6].

3.2.1

The Current Situation

There is a need of increased usage of natural gas and adequate arrangement of storage and transportation across the country. In 2019, India was the 4th largest importer of LNG, importing about 1.2 Tcf, out of a total demand of about 2.1 Tcf [13]. In FY20, India produced about 1.1 Tcf LNG, while imported about 0.76 Tcf LNG [7], and these figures are going to be ever increasing. Huge storage facilities are required to support this need, and a plan has been launched recently to develop 1000 LNG stations in the coming years, out of which, foundation stone for 50 stations have been laid already [14]. The current pipeline fabrication trend is around 100 km/year. The steel required for oil and gas pipelines must fulfil some specific quality aspects, such as high strength (different levels based on application), combined with superior lowtemperature fracture toughness (more than 90% shear area under drop weight tear testing at –30 °C). The quality requirement is more stringent for the transportation of crude oil and sour gas. The present pipeline projects (IOCL, ONGC and GAIL) would require high quantity of API X70 grade steel in near future. The energy sector mix, global vis-à-vis India, as of 2019, is schematically presented in Fig. 6 [15]. This clearly indicates that India is still very much dependent on coal, and way behind the world in utilising clean and renewable energy. Use of natural gas in 2019 was only about 6.3% in India, as against 24.2% in the world. Irrespective of the source of energy, whether it is based on fossil fuels, nuclear reaction, or renewable sources like wind, solar or geothermal, steel always has a crucial role to play in creating the infrastructure for the production and distribution of energy, ensuring ample usage of steel. Some of the areas of renewable energy are as follows:

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B. Bhattacharya and D. Bhattacharjee Energy sector mix World (2019)

54.67%

India (2019)

24.20%

4.30%

1.17%

Nuclear Energy

5.00%3.55%

6.40%4.23%

Renewable Energy

Hydroelectricity

27.00%

33.10% 30.06%

6.31%

Natural Gas

Coal

Oil

Fig. 6 Energy sector mix, global vis-à-vis India, 2019 [15] (Courtesy of BP)

• Biomass: Extensive use in agriculture. • Solar: Steel plays a key role in converting solar energy into electricity or hot water. It is used as a base for solar thermal panels and in pumps, tanks and heat exchangers. • Wave and tidal: A steel pile is the main component of a tidal turbine in tidal energy systems. Steel is also used to fabricate wave energy devices. The steel for this application must be appropriately resistant to corrosive marine environment. • Hydroelectricity: Steel is needed to reinforce the concrete dams. • Wind: Steel is the main material used in onshore and off-shore wind turbines. Almost every component of a wind turbine is made of steel, from the foundation to the tower, gears and casings [16]. Steel provides the strength for taller and more efficient wind turbines. • Hydrogen: This is an important source of clean energy for future world, in a journey towards carbon-free economy. Renewable energy is required to produce green hydrogen. Japan started recently the largest green hydrogen plant, with a 20 MW solar energy system, which feeds a 10 MW electrolyser plant [17]. In India also, the recent roadmap development of 2016 includes the scope of extensive R&D on developing advanced electrolysers, and high-pressure storage and transportation equipment, which means gas tanks, pipelines and cryogenic liquid hydrogen trucks. All these will require usage of advanced structural steels. Ministry of New and Renewable Energy, in partnership with NTPC, has proposed to launch a pilot project on fuel cell buses. Interesting to note that a hydrogen fuel cell bus prototype has already been launched by Tata Motors in 2019, in collaboration with ISRO and IOCL [18]. Out of all these applications, the wind power generation system is going to play a very important role in future development of the country. The wind turbine towers are basically tubular steel structure, carrying a rotor and a nacelle at the top, which can weigh as much as 300 tonnes [16]. Structural steels are the only solution for this segment. Longer rotor blades and taller towers are required to maximise power

Steel as a Structural Material

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Electricity from renewable energy sources in billion units 126.76 101.84

94.36

81.51 65.78

FY16

FY17

FY18

FY19

FY20* *Upto November 2019

Fig. 7 Electricity generation from renewable energy sources in billion units (as of November 2019) [7] (Courtesy of India Brand Equity Foundation)

Installed capacity for renewable energy sources in GW 37.5 33.7

10.0 4.7

Wind Power

Solar Power

Bio-Power

Small Hydro

Fig. 8 Installed capacity for different renewable energy sources in GW, (as of December 2019) [7] (Courtesy of India Brand Equity Foundation)

generation, which means the usage of high strength structural steel in huge quantity. In India, the renewable energy generation is still behind the global figure (Fig. 6). However, there is an increasing trend over the past few years, (see Fig. 7) [7]. The importance of wind power within the class of renewable energy is depicted in Fig. 8 [7]. India today is ranked 4th in wind power, 5th in solar power and 5th in overall renewable power installed capacity, as of 2018. According to the 2018 Climatescope report, India is ranked 2nd among the emerging economies to lead the transition to clean energy.

3.2.2

The Growth Prospect in Medium Term (by Around 2025)

The total demand of electricity in India is expected to be around 1905 TWh by 2022 [7]. In the clean energy sector, usage of natural gas is going to play a key

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Addressable market size (KT)

1050

1105

1160

1220

FY17

FY18

FY19

FY20

1410

1555

1345

1480

1280

FY21

FY22

FY23

FY24

FY25

Fig. 9 Estimated market demand for the steel required for pipeline (CAGR 5%) Share of renewable energy in total electricity consumpon Solar

Non-solar

Total 21.00% 19.00% 17.50%

17.00% 14.25% 11.50% 8.75%

10.25%

9.50%

10.25%

10.50% 10.50%

10.25% 8.75%

6.75%

7.25%

FY19

FY20

4.75% 2.75%

FY17

FY18

FY21

FY22

Fig. 10 Share of renewable energy in the power consumption of India [21] (Data: Courtesy of Kumar and Majid, 2020)

role. The projected market size of steels for pipeline, up to 2025, is shown in Fig. 9, indicating an expected rise of more than 25%. Regarding renewable energy, as a part of Paris agreement, Government of India has now set a target of enhancing the installed capacity from 85.9 GW to 175 GW by 2022. As per an article published in Electrical India in 2016 [20], the expected capacity of wind power by 2022 would be around 60,000 MW, while the solar power capacity would be around 100,000 MW, followed by bio-mass and small hydro-power capacities around 10,000 and 5000 MW, respectively. A trend of gradual enhancement of renewable energy during the period FY 2016–17 to FY 2021–22 is presented in Fig. 10 [21]. Last, but not the least, in the same period, the aim of enhancing thermal power capacity in India is by around 47.86 GW, over and above the present capacity of 199.5 GW in 2020 [7], and it is obvious that structural steels would be required for the installation of all types of power plants.

3.2.3

The Growth Prospect in Long Term (by Around 2030)

The International Energy Agency (IEA) forecasts a 30% rise in global demand for energy by 2040, most of which will come from developing countries. In India, there

Steel as a Structural Material

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is currently a focus on increasing the use of natural gas to about 15% of the energy mix by 2030 [22]. The estimated demand of natural gas is going to be about 5.0 Tcf by 2040 [7]. For hydrogen, as a source of clean energy, the demand is expected to rise by 3–10 times by 2050 [18]. All these are great opportunities for steel sector in India, as the “Make in India” drive is also going to encourage internal production of high-quality structural steels for new pipelines, instead of importing the material. As far as the renewable energy source in India is concerned, the Government has an aim of installed electricity generation capacity to 40% by 2030 [7], and the investment in this area may be of the order of US$ 500 billion by 2028.

3.3 Mobility Over past several decades, the automobile sector has seen some significant transitions. In earlier days, a car used to be treated as a luxury item, affordable mainly by the rich. The automobile body used to be built with thick steel sheet, and the vehicles generally used to be large and heavy. This is true in Indian perspective as well. Heavy cars like Ambassador ruled over Indian roads for several decades. The concept of low emission and fuel efficiency came later, when it was realised that controlling the emission level was essential for the sustenance of mankind. Automobile manufacturing technology has therefore a critical role to play in this regard.

3.3.1

The Current Situation

On one hand, there is a need to save the fossil fuel reserves. On the other hand, there is even a greater need to mitigate the environmental pollution. Driven by government policies, the automobile manufacturing industry responded to these challenges with a series of solutions, such as stricter emission norms, small size lightweight cars with higher fuel efficiency, advanced technology for the fuel-efficient engines and transmission systems, usage of advanced high strength steels to ensure passenger safety. Despite all these efforts, pollution level has kept on increasing due to burgeoning number of vehicles on the road. It is high time to look further ahead to find out innovative solutions for fulfilling the need of mobility, instead of just continuing with existing concept of automobiles with some incremental improvements year on year. The need of breakthrough solutions has given rise to the concept of electric vehicle for the days to come. The development of the family of advanced high strength steels (AHSS) (Fig. 11) [23] came as a revolution, which led to a massive technological boost in automobile industry. Figure 12 depicts how the application of high strength steel gradually increased in automobile manufacturing industry [24]. Optimisation is the keyword in the application of material for manufacturing of automobile components, which involves the design of component, vis-à-vis design of material, depending on the specific role of the component. The second-generation AHSS mainly consisted

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Elongaon (%)

50

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First generaon AHSS DP, TRIP, CP, Martensic 2002-2012

IF-HS

40 MS 30

ISO BH TRIP

C-Mn

20

HSLA DP/CP

10

Martensic

0 0

300

600 900 Tensile strength (MPa)

1200

1500

Fig. 11 Tensile strength and elongation of various automotive steel grades [23]

Market penetraon by AHSS grades 350 2000

300

2005

2007

2009

2020*

250 200 150 100 50 0 DP

Boron

Martensite

TRIP-CP-RA

AHSS (other)

*Projected market penetraon by 2020

Fig. 12 Increased usage of advanced high strength steel grades [24]

of single-phase austenitic steels, combining strength as high as 1000 MPa along with elongation as high as 70–80%. However, usage of these steel grades has been fairly limited due to the factors like high cost, heavy alloying, difficulty of steel making and the like. The research interest then gradually shifted to developing thirdgeneration AHSS. The goal is to achieve multi-phase microstructures with leaner composition but enhanced strength and ductility (Fig. 13) [25]. Researchers are now mainly engaged in developing innovative processing routes for the stringent control of microstructure [26–30]. According to the International Organisation of Motor Vehicle Manufacturers, 91.8 million vehicles were manufactured in 2019. On an average, 900 kg of steel is used

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13

Fig. 13 Schematic representation of the position of third-generation AHSS [25] (Courtesy of WorldAutoSteel)

per vehicle, out of which, about 40% is used in the body structure, panels, doors and trunk closures for high strength and energy absorption in case of a crash. About 23% of steel is used in the drive train, while about 12% is used in the suspension, using rolled high strength steel strip. The remaining steel is used in wheels, fuel tank and other auxiliary systems. In today’s vehicles, advanced high strength steels constitute as much as 60% of the body weight, making lighter, optimised vehicle designs, ensuring safety and improved fuel efficiency [31]. The new grades of AHSS enable car makers to reduce vehicle weight by 25–39% compared to conventional steel, leading to a net weight reduction of about 170 to 270 kg, for a standard 5seater family car. This means a lifetime saving of 3 to 4.5 t of greenhouse gases over the vehicle’s total life cycle, which is more than the total amount of CO2 emitted during the production of all the steel in the vehicle. Indian automobile segment is currently going through a transition from BS IV to BS VI, as Government of India is also implementing stricter norms for pollution control. Regarding safety, though the crash test performance at global standard is not encouraging for most of the Indian car models [32], awareness is gradually picking up among the Indian consumers, which is already prompting the car manufacturers to offer better safety features even in base models. As on 2018, India is 4th largest automobile market in the world. The gradual rise in production and sale figures over the years are presented in Fig. 14 [7]. The graphs reveal a steady growth till FY19, with a CRGA little less than 7%, the economic setback being clearly reflected in the figures of FY20. The segment-wise domestic market share of different types of vehicles and export figures are presented in Fig. 15. Figures 14a and 15a together indicate that during FY19, the number of passenger vehicle production was more than 4 million, including all kinds of cars (small cars, mid-size or large sedans, SUVs, etc.). Despite the economic downfall during FY20, there was a sale of 15,000 luxury cars during April-September 2019, while the sale of premium luxury bikes was 14,000 [7].

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(a) Number of automobiles produced in India (in millions) CAGR 6.96% 29.07 20.65

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FY14

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18.42

19.72

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FY14

FY15

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26.27

21.86 16.47

FY16

FY17

FY18

FY19 FY20* *ll January 2020

Fig. 14 Trends of automobiles produced and sold in India; a automobiles produced, b automobiles sold [7] (Courtesy of India Brand Equity Foundation)

The journey of light weighting in this new era may not be completely restricted within AHSS. While there is an increasing trend of using high strength to ultra-high strength steels in automobile body manufacturing, [33], the light-weighting drive is even replacing steel with some light metals like aluminium or magnesium, or with some non-metallic components as well (Fig. 16) [34]. Cost is a very important driving factor, and steel has an edge over other materials in this aspect. Components made of

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Number of automobiles exported (in millions)

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Passenger vehicle

Source: India Brand Equity Foundaon

FY13

FY14

FY17

FY18

FY19

Source: India Brand Equity Foundaon

Fig. 15 Status of production and export as of FY19; a segment-wise domestic market, b number of automobiles exported [7] (Courtesy of India Brand Equity Foundation)

aluminium or magnesium alloys are definitely being used in modern cars, but those are mainly in the very high-end cars. However, the market is driven by volume, and middle-class economy dominates the volume. Therefore, it is difficult to replace steel as a structural material, as far as overall automobile industry is concerned. Steel is being replaced even in small and cheaper cars, where it is adequately cost effective. For example, all the bumpers are nowadays made with plastics or polymers. In twowheelers, components like front fender, engine head cover, chain case cover, etc. are now being made of plastics and polymers. In order to reduce the use of fossil fuel, as well as emission, the entire world is now inclined towards electric driven mobility. The number of EV models is rising quite rapidly, with some significant improvement in battery range as well (nearly 450 km in single charge). By 2020, we can already see many EV models available in the market [35], which indicates that electric vehicles are now ready to capture the market in almost all segments. The main driver for this electrification race is again affordability. Lithium-ion battery prices have dropped about 75% since 2013, hitting $176/kWh in 2018 (Fig. 17) [35]. Apart from that packaging efficiency and the cell energy density also are improving. Steel, being significantly cheaper than other materials, is again the most suitable structural material for EVs. For example, the 2011 Nissan Leaf EV components were made of aluminium, while the recent 2019 Nissan leaf EV closures are made of steel. The advantages of steel, in general for EVs, are as follows [36]: • Narrower and compact transverse electric powertrains, leading to shorter front end, with increased occupant space. • Lack of an exhaust system and fuel tank/filler leads simplifies the design of many components such as cross members. • Higher safety requirement for the protection of high voltage electric powertrain and large, under-floor battery pack (300 L, 500 kg). • The EV body structure load path requirements are ideal for AHSS application. • The floor cross members, being straight, can use very high-strength martensitic roll-formed sections.

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1970: Total weight 1100 kg Steel and iron Aluminium Magnesium

Other non-ferrous metals Plascs Elastomers Others

2000: Total weight 1400 kg

2010: Total weight 1150 kg

Fig. 16 Trend of development of materials for construction of a mid-sized car [34]

Lithium-ion baery prices (volume-weighted averages), $/KWh $650 Cell

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$185

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Fig. 17 Li-ion battery cost over the years [35] (Courtesy of Business Council for Sustainable Energy)

• Safety is a serious concern, as EVs are different in nature, because of the high voltage electric system. Some of the applications of steel in this regard are listed below

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Application

Material

Cross members

Third-generation AHSS, with strength more than 1000 MPa and over 20% elongation

Frontal crash load management

Third-generation AHSS

Minimise passenger/battery compartment intrusions Structural members like rocker, rails, cross members, pillars

AHSS or UHSS

Battery enclosure

AHSS and Third-generation AHSS (for better protection from road-debris impact on the bottom of the vehicle)

3.3.2

The Growth Prospect in Medium Term (by Around 2025)

On the recovery from the recession period, it is expected that Indian automobile sector will grow at a considerable pace, reaching Rs. 16–18 trillion by 2026. This is rightly supported by the Automotive Mission Plan of India Government 2016–2026 [7]. Since the automobile production in India offers significant cost advantage, the OEMs can save 10–25% on operations. The rise in middle-class income and young population is also a positive factor in this regard. All these prompt Government to focus on developing India as a global manufacturing and R&D hub. Foreign investment of 8–10 billion US$ is expected by 2023; accordingly, the export figure is expected to become 5 times during 2016–2026. Market growth in automobile sector means lot of high-end usage of steel. With all the positive signs, the Indian automobile sector is again expected to pick up pace in the post-recession era.

3.3.3

The Growth Prospect in Long Term (by Around 2030)

It is expected that urban transportation globally will be dominated by electric and automated vehicles within another 10–15 years [35]. The scenario is quite similar in India also. All the frontline vehicle manufacturers have engaged in a war for capturing the EV market, thanks to the policy of India Government, which aims at making India a 100% electric vehicle nation by 2030 [37]. This is perhaps a difficult target, but for sure, a large fraction of vehicles on Indian road will be replaced by EVs. It is interesting to note that electric buses for public transport are already being seen in some Indian cities.

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4 Indian Defence Sector—Long Term Prospect Application of structural steels is an integral part of defence industry. Steels in various forms, such as cold finished bars, hot rolled bars and round bars, are used in the manufacturing of missile components, shell casings, morters, track pins, etc.; high strength structural steel plates are used in the fabrication of ship and submarines, military trucks, ballistic resistant armoured vehicles, etc. India is one of the major importers of defence equipment, which requires a huge budget. The allocated defence budget for FY20 was INR 305,296 Cr, while the capital expenditure was INR 103,394 Cr [38]. The capital expenditure projection by 2025–26 is INR 296,514 Cr [39], which means a nearly threefold increase in another 5 years. The most important point at this stage is that India is now inclined towards complete indigenisation of strategic industries, such as railways, defence, etc. through launching the drive “Har Kaam Desh Ke Naam” [40]. This is indeed going to be a significant boost to Indian steel industry. The effect of the drive for indigenous development initiative is already seen as India has started manufacturing high-quality strategic equipment like light combat aircraft, Tejas, and light combat helicopter, the HAL-LCH. The main usage of structural steel would be in battle tanks, ships and submarines, armoured trucks and vehicles, etc. The first indigenous aircraft career of India, INS Vikrant, weighing more than 40,000 tons, is already under fabrication in Cochin Shipyard. Nuclear-powered ballistic missile submarines, each weighing about 6000–7000 tons, are also being manufactured in India. INS Arihant is the first one of this series, which is already in service since 2016, and the second one, INS Arighat is now under sea trial, two more being in production stage. Initiatives for indigenous development and manufacturing of battle tanks and armoured vehicles are also in progress (for example, Arjun Mk1A rugged battle tank, weighing 68 tons). All these are good signs for Indian steel industry, as there would be ample opportunity for the development and production of advanced defence grade structural steels through advanced research.

5 Technology and Infrastructure Gaps Apart from Dual Phase steel, the applications of other AHSS grades in India are still very limited. However, the leading steel makers of other advanced countries like USA, UK, Japan, Korea, Germany, France or Austria have at least their manufacturing capabilities ready for such steel grades. On the other hand, due to inadequate demand of such advanced steel grades, India is still in a stage of development and trials. Cost is always an important factor, and so, the specific requirements for the automobile segment are fulfilled by importing the material. Therefore, it is also difficult to predict how many years it would take to use AHSS grades in areas other than mobility. When India is on the track of huge development in the coming years, with possibilities of construction of high-rise buildings, roads and railways at tough geographical locations, there will be need for catching up with developments in the

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field of high strength steels. Although construction of large dams is always a threat to nature, the prospect of constructing dams of different sizes with different purposes cannot be completely ruled out in a developing and power-hungry country like India, and all these constructions would lead to usage of structural steels. The supporting manufacturing capabilities should also be developed either by installation of new facilities or by augmentation of existing mills.

6 Scope of Research Activities and Way Ahead As far as the application of steel as a “structural material” is concerned, it is quite clear that not only it is difficult to replace steel now, it is impossible to replace steel in almost all areas for decades ahead. This is applicable for the entire world, and more for the developing countries like India. The rise in steel demand is closely related to the demand–supply balance, as well as to the development level and per capita steel consumption in different countries. Currently steel industry is going through a recession period, which is a matter of concern. Despite the downfall during 2019, the steel demand was expected to rise gradually during 2020 [41]. However, the expected growth could not be seen due to worldwide COVID-19 pandemic situation, which is a serious blow to entire world economy. India is one of the most affected countries in this situation. Now, the effective rise in steel demand is expected to be deferred by a year and expected only toward the later part of 2021. However, the National Steel Policy 2017 foresees a demand of about 300 Mt of steel by 2030–31 [7], which appears to be an encouraging factor under present circumstances.

6.1 The Current Situation of Research on Structural Steels Per capita consumption of steel in India is way below the world average [3, 4]. Being a highly populated developing country, India is going to use huge quantity of structural steel in all possible segments in the coming years. The timely stands taken by the Indian Government in different areas, such as green energy, green building and green mobility are strong driving forces towards the development of new generation high strength steels. Accordingly, it may be envisioned that adequate research support would be required in developing such steel grades.

6.2 Scope of Research in Medium Term (by Around 2025) It appears difficult to imagine the development of some completely new steel grades and successful commercialisation of them within next five years. Catering for the market in 3–5 years from now (till 2025) will essentially require improvement and

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incremental research activities on some of the standard steel grades that already exist. Some of the development activities may be as follows: • High strength micro-alloyed steels for infrastructure and construction • High strength steels for manufacturing lifting and excavation equipment • In-house development and commercialization of AHSS grades like complex phase (CP) steel • Steels for building construction with improved seismic resistance • Steel for structural applications with improved fire resistance • High strength steels for taller windmills • Developing and commercialising steels for pipeline, up to API X80 • Further improvement of advanced high strength steels, combining GPa level strength with appreciable elongation (20% or more) • Steels that can combine difficult properties like high strength, high stretch forming, high hole expansion • Developing steels for hot forming that will need no coating • Understanding the property requirements for different steel components of EVs, particularly battery chamber components, and research for developing appropriate materials to achieve them.

6.3 Scope of Research in Long Term (by Around 2030) The world is changing fast, driven by some critical factors like population growth, rise in pollution level and global temperature, ever-decreasing fossil fuel reserve, everincreasing number of automobiles on road and the like. The effects are already visible, as the governments of all the countries worldwide, India being no exception, are coming up with new and stricter policies, with an aim of protecting the mankind from possible disaster. Therefore, while considering the application of steels by the year 2030, it is most important to visualise the situation after ten years, which is a difficult task at this stage, as it involves new possibilities and uncertainty factors. Despite this uncertainty, it may be safely assumed that steel will continue to be the cheapest and strongest material, and therefore, a superior choice for structural application. Based on this assumption, some of the research areas for steel development may be as follows: • Advanced steel production technology, to drastically cut down the carbon footprint and the cost of production • Alternative and renewable fuel to completely replace the use of carbon or fossil fuel in iron making • Alternative and auxiliary processing technology for developing ultra-high strength novel steels with high elongation • Development of lightweight steel with high stiffness, requiring innovative processing route

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• Development of a large family of third-generation AHSS, to combine very high strength (over 1500 or 2000 MPa) with high ductility and appropriate forming properties • Advanced steels for battery casing and chassis for electric vehicles • Development of stronger and lightweight composites with steel base • Design and development of advanced steel-based structures for effective thermal management of future generation green buildings and cabins of electric vehicles • New and wider applications of AHSS, over and above in automobile sector.

7 Concluding Remarks Steel is the most versatile and most easily affordable structural material, which finds a wide range of applications in present days, out of which, a few prominent ones have been discussed briefly in the present article. Due to some unique qualities, such as versatility of mechanical properties with relatively simple chemical compositions, cost competitiveness, recyclability, steel clearly has an edge over other structural materials. India, being a highly populated developing country, is doing fairly well in steel manufacturing sector, as the country has already occupied the second position in the world of crude steel production. The per capita steel consumption figure in India is also improving, although still below the world average. All these indicate that there is ample opportunity for growth and development in India. Considering some of the most important areas of development, such as construction of highways and other infrastructures, railways, clean energy, mobility, defence, etc., it may be anticipated that the period of next 5–10 years is going to be a crucial one for India, as the nation is already going through a significant transition stage. On one hand, there is a pressure of infrastructure development at a faster pace, while on the other hand, the expense has to be reasonably under control. In order to be both economically sustainable and technologically superior, the “Make in India” drive is actually boosting the Indian industry, and also throwing some healthy challenge. The issue of environment and conservation of nature are going to enhance this challenge by several times. The Indian steel industry will have to fulfil the expectations of the nation, not only by supplying the huge quantity of steel, but also by coming up with innovative solutions for future generation advanced structural steels through green technology.

References 1. H. Akanuma, The significance of the composition of excavated iron fragments taken from Stratum III at the site of Kaman-Kalehöyük, Turkey. Anatolian Archaeol. Stud. 14, 147–158 (2005) 2. Ironware piece unearthed from Turkey found to be oldest steel, The Hindu. Chennai, India. 2009–03–26. Archived from the original on 2009–03–29.

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3. Per capita steel consumption in India a third of global figure: Study, Business Standard, 2019– 06–07. 4. Quality and consumption of steel, Ministry of Steel, posted on 2019–07–10 by PIB in Delhi. 5. World steel in figures, World Steel Association, (2019). https://www.worldsteel.org/ 6. List of countries by steel production. https://en.wikipedia.org/wiki/List_of_countries_by_ steel_production 7. India Brand Equity Foundation. https://www.ibef.org 8. Constructsteel. https://constructsteel.org/ 9. India Services – Construction and related engineering services; Ministry of commerce and industry – Government of India. https://www.indiaservices.in/construction 10. Construction Sector: Current Scenario and Emerging Trends. https://www.nbmcw.com/report/ construction-infra-industry/1835-construction-sector-current-scenario-and-emerging-trends. html 11. World Green Building Council. https://www.worldgbc.org/embodied-carbon 12. Indian Railways Statistical Publications 2016–17, Ministry of Railways 13. U.S. Energy Information Administration; Petroleum Planning and Analysis Cell, Natural Gas, Consumption. https://www.ppac.gov.in/content/152_1_Consumption.aspx 14. A. Bajic, India kicks off 1000 LNG stations development, OUTLOOK & STRATEGY. (2020) https://www.offshoreenergy.biz/topic/outlook-strategy/ 15. BP Statistical review of world energy. (2020). https://www.bp.com/en/global/corporate/ene rgy-economics/statistical-review-of-world-energy.html 16. Steel Solutions in the Green Economy: wind turbines. (2019). https://www.worldsteel.org/ 17. W. Hall, Driving India towards the clean energy technology frontier. The Energy and Resource Institute (TERI), New Delhi, India. http://www.teriin.org/ 18. Fuel cell and hydrogen development in India, Fuel cell and hydrogen energy association, Washington, USA. www.fchea.org/in-transition/2020/6/9/fuel-cell-and-hydrogen-development-inindia 19. Life cycle cost efficient near zero construction. https://www.slideshare.net/Ruukki/energy-eff icient-solutions-for-steel-structures-case-study-of-a-near-zeroenergy-building 20. J. B. Thakar, Future perspective for renewable energy in India, in Electrical India, (2016). https://www.electricalindia.in/future-perspective-for-renewable-energy-in-india/#:~:text=Ren ewable%20energy%20in%20India%20comes,power%20from%20April%202016%20levels 21. C.R. Kumar, M.A. Majid, Energy. Sustainability and Society (2020). https://doi.org/10.1186/ s13705-019-0232-1 22. India 2020 Energy Policy Review, International Energy Agency. https://niti.gov.in/sites/def ault/files/2020-01/IEA-India%202020-In-depth-EnergyPolicy_0.pdf 23. High Strength Steel Application Guidelines, International Iron and Steel Institute, 2005, “www. worldautosteel.org” 24. A. Abraham, Ducker Worldwide, Future Growth of AHSS [Presentation at Great Designs in Steel Seminar–2011] (2011) 25. Global formability diagram, (2021). https://ahssinsights.org/blog/a-new-global-formabilitydiagram/ 26. R. Rana, Editorial – “Special issue on medium manganese steels.” Mater. Sci. & Tech. 35(17), 2039–2044 (2019) 27. R. Schneider, K. Steineder, D. Krizan, C. Sommitsch, Mater. Sci. & Tech. 35(17), 2045–2053 (2019) 28. A. Arlazarov, M. Goune, O. Bouaziz, F. Kegel, A. Hazotte, Mater. Sci. & Tech. 35(17), 2076– 2083 (2019) 29. Y. Li, F. Huyan, W. Ding, Mater Sci & Tech. 35(2), 220–230 (2019) 30. D. Raabe, Medium Mn Steels. http://www.dierk-raabe.com/medium-mn-steels/ 31. https://www.worldsteel.org/steel-by-topic/steel-markets/automotive.html 32. Global NCAP. http://www.globalncap.org/results/ 33. C. Lesch, N. Kwiaton, F.B. Klose, Steel Res. Intl., 87, 2076–2083. https://doi.org/10.1002/srin. 201700210

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34. M. Winterkorn, Weltweite Landesspezifische Fahrzeuganforderungen fur Material und Funktion, Dresdner Leichtbausymposium, Dresden, Germany (2002) 35. Sustainable Energy in America Factbook (2019). https://www.bcse.org/wp-content/uploads/ 2019-Sustainable-Energy-in-America-Factbook.pdf 36. D. E. Malen, Mass Benchmarking Analysis of Electric Vehicles, A2Mac1, WorldAutoSteel 37. Government Plans to Make India 100% Electric Vehicle Equipped Nation by 2030, NDTV Car & Bike team (with inputs from PTI), (2016) http://auto.ndtv.com/news/government-plansto-make-india-100-electric-vehicle-nation-by-2030-1291032 38. L. K. Behera, India’s Defence Budget 2020–21, The Institute for Defence Studies and Analysis. (2020). https://idsa.in/issuebrief/india-def-budget-2020-21-lkbehera-040220 39. INDIAN DEFENCE INDUSTRY – An Agenda for Making in India, Laxman Kumar Behera, The Institute for Defence Studies and Analysis, New Delhi, Pentagon Press, (2016) 40. Press Information Bureau, Government of India, (Release ID: 1603416), Posted On: 17 FEB 2020, “https://pib.gov.in/PressReleseDetailm.aspx?PRID=1603416” 41. Worldsteel short range outlook, (2019). https://www.worldsteel.org/media-centre/press-rel eases/2019/worldsteel-short-range-outlook-2019.html

Aluminium As a Structural Material Saikat Adhikari, Vilas Tathavadkar, and Biswajit Basu

1 Introduction Owing to its set of unique properties, aluminium is one of the key engineering materials used for structural applications across the automotive, aerospace, mass transportation, ship building and power industry segments. Not surprisingly, its global production has been steadily increasing since the beginning of the twentieth century and it is 3rd most produced material after steels and plastics (Fig. 1) [1]. The global trends of consumption also do not indicate any slowdown (Fig. 2) clearly proclaiming aluminium as a metal of the future. Globally transportation, building and construction, packaging and power industries are the biggest consumers for aluminium (Fig. 3). In India, the scenario changes slightly with power and transportation sectors being the primary drivers due to rapid electrification and urbanisation. China, India and the Middle East, in particular, have seen phenomenal growth in aluminium consumption over the past few decades and continue to dominate growth estimates in the near future (Fig. 4). Building, construction and packaging are the major growth segments in India and China. Aluminium is consumed globally in the form of castings (e.g. automotive engine blocks), forgings, wires and cables (power distribution), flat rolled products (automotive sheets, beverage cans, cookware, roofing, cladding etc.) and extrusions (structural components in construction, transportation etc.). Rolled products and extrusion segments dominate global applications of aluminium primarily due to extensive use of aluminium in packaging, cladding, sheets for automotive body and structural components in building, construction and auto sector. In India, wires and cables form the largest application segment due to electrification followed by automotive castings (Fig. 5). Flat rolled products with extrusions is just 23% in India compared with 63% globally, indicating a huge potential growth area [5]. Projections indicate that aluminium consumption in India is poised to grow from 3.3 Mt in 2016 to 5.3 S. Adhikari · V. Tathavadkar · B. Basu (B) Aditya Birla Science & Technology Co. Pvt. Ltd., Taloja, Maharashtra, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_2

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Fig. 1 World production volumes for various metals and plastics [1]

Fig. 2 Expected global consumption trend for aluminium from 2016–2023 [2]

S. Adhikari et al.

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Fig. 3 Aluminium consumption by industry segment 2015 [3]

Fig. 4 Global aluminium consumption by regions [4]

Mt in 2021 and 8.0 Mt by 2025 propelled by government initiatives like Make in India, Smart Cities, Housing for all, rural electrification and freight corridors [6].

2 Driving Aluminium Growth Globally, with increasing regulatory pressures to reduce CO2 footprint across industries and market segments, the aluminium industry is not only preparing to respond to the potential threat but also looking at it as a great opportunity for pushing aluminium growth. Aluminium producers are increasingly looking at ways to improve energy

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Fig. 5 Consumption of aluminium by product segment (2015) [5]

efficiencies across the aluminium value chain by reducing energy consumption in smelting, improving efficiency of rolling, extrusion, homogenisation, annealing processes etc. and also actively evaluating technological breakthroughs such as low carbon smelting technologies. Simultaneously, aluminium producers are leveraging the unique combination of properties of strength to weight ratio, conductivity and recyclability of aluminium to come up with new age materials and solutions with improved functionalities that can potentially reduce the world’s energy consumption trends.

2.1 Transportation Aluminium is indispensable to the aviation industry; more than 60% of the structural weight of the largest commercial aircraft today is made up of aluminium alloys. Its lightness improves fuel efficiency, significantly decreasing CO2 emissions and reducing subsequent environmental impact. The aluminium content in cars and commercial vehicles such as trucks and trailers also continues to increase, replacing heavier components made from other metallic materials. A new passenger vehicle sold in the European market today contains on average 150 kg of aluminium, compared with 100 kg in 2000 [7]. Conventionally, automotive OEMs have been using 6xxx alloys for outer body sheets and 5xxx for inner panels. However, more recently there is a shift towards using more of AA6xxx alloys [7]. The transition is promoted by OEMs demanding higher strengths, which are more readily achieved using the AA6xxx alloys. While 5xxx series alloys have excellent strength-to-weight ratios, formability properties and full recycling compatibility, 6xxx series have the upper hand as they are versatile, heat-treatable, highly formable and easier to weld. Figure 6 shows the UTS

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29

Fig. 6 UTS and % Elongation of 3xxx, 5xxx, 6xxx and 7xxx aluminium alloys [7]

and elongation values (A80) for various alloy options in conventional 5xxx and 6xxx alloys along with the targeted high strength options in 6xxx and 7xxx series. Various alloys such as AA6009, AA6010, AA6022 and AA6111 have been used as outer body panels in North America, while AA6016A has been the predominant choice in Europe [8]. Most of the major aluminium sheet suppliers such as Novelis, Aleris, Constellium, Hydro and Amag produce the AA6016A alloy. AA6016A is a less strong but more formable alloy that has a lower bake hardening response than AA6111. The OEMs use AA6016A at relatively thicker gauges compared with AA6111 to obtain the same level of dent resistance. AA6111 and AA6016A have progressively been replaced by AA6451 which has a lower copper level (60 IACS), UTS ~ 180 MPa and a heat resistance of around 80 °C making them suitable for aluminium conductor steel reinforced (ACSR) and all aluminium conductors (AAC). For higher strength requirements, 6xxx alloy conductors particularly AA6101 and AA6201 are used, which provide strengths up to 320 MPa with a maximum of 50 IACS conductivity but thermal resistance up to 80 °C. Considerable research has focussed on development of Al–Zr based High Temperature Low Sag (HTLS) conductors which can provide thermal resistance up to 230 °C, while maintaining the room temperature properties of > 60 IACS conductivity and UTS > 160 MPa [12]. Nanostructured 6xxx aluminium alloys with high strength (290– 320 MPa) and conductivity (up to 57.5 IACS) are also in developmental stage. These alloys are being produced by the formation of ultrafine grains by applying severe plastic deformation via equal channel angular pressing (ECAP) process [13].

2.5 Consumer Goods Aluminium has many domestic uses, particularly in the kitchen. Many day-to-day utensils and kitchen appliances use aluminium, with its heat conductivity ~2.5 times higher than steel—making it an ideal material for pots, pans and baking materials. Manufacturers are also increasingly incorporating aluminium into a variety of electronic equipment, including TVs, tablets, laptops, and smartphones. Aluminium casings are light and strong, aesthetically pleasing and offering greater robustness and reliability than plastic. Indeed, aluminium is increasingly viewed as an indicator of premium quality in electronic devices.

2.6 India Growth Drivers Closer home, most of the demand in India is expected to come from the power sector where investments from the state electricity distribution companies and central government schemes totalling Rs. 4.3 trillion are being planned over the next five years to expand India’s transmission and distribution network. The electrical sector consists of machinery and equipment for the generation, transmission and distribution of electricity. The regulatory restrictions on CO2 emissions, rollout of BS 6 norms and the central government’s push for electric vehicles is also nudging automotive OEMs towards reducing vehicle curb weight and also announcing launch of several EV models. Particularly in India, the 2–wheeler and Light Commercial Vehicles (LCVs) also have tremendous potential in the EV segment. Lighter weight

Aluminium As a Structural Material

33

of vehicles will have a significant bearing on battery capacity and drivable range (and hence battery weight). These have opened up new opportunities for aluminium application, which were earlier restricted due to cost implications of replacing steel with aluminium. Aluminium also has tremendous potential in the mass transportation segment including bus body, railway wagons, high speed and metro rail. Also, the government’s push to build Smart Cities coupled with the growing urbanisation has encouraged light-weight infrastructure solutions where aluminium can fit into applications like facades, window panels, curtain walling, structural glazing, roofing and cladding applications [6]. Lastly, due to the Make in India push, requirements in defence, aerospace and space applications which were traditionally imported are increasingly being fulfilled by domestic suppliers. They are therefore looking at huge investments along with government support to install new capabilities to support these strategic sectors.

3 Aluminium Towards a Sustainable World Currently the aluminium industry emits about 1 billion of 50 billion tonnes of greenhouse gas emissions produced around the world each year. With increasing primary production required to meet global demands, there is going to be further increase in the emissions. The aluminium industry has been working to reduce its carbon footprint through the development of high efficiency, low emission production technologies. However, access to carbon-free energy such as hydropower or nuclear is currently limited and most of world’s primary aluminium is currently produced using coal and gas power. Hence in addition to decarbonisation of primary aluminium production, the industry is actively looking at reducing overall energy consumption in the smelting process by use of drained cathode cells and inert anodes in HallHéroult process or alternative technologies such as direct carbothermic reduction of alumina to aluminium using carbon and heat. Recently, ALCOA, RTA and Apple have jointly announced the ELYSIS technology for aluminium production, which uses inert anode and claims to extend anode life by around 30 times (about 2.5 years) compared with the carbon anode and reduce the operating cost by 15% [14]. On the aluminium products side, the aluminium industry is continuously striving to offset the environmental impact of urbanisation by providing innovative and sustainable solutions to modern day challenges. The major areas where the aluminium industry is impacting the drive towards sustainability are described below.

3.1 Light-Weighting In a bid to comply with the increasingly stricter environmental regulations, automakers are resorting to light-weighting and aluminium has emerged as a material of choice in many new applications. It not only leads to an improvement in fuel

34

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economy but also leads to better performance and control and improved safety due to lighter weight of the vehicles. More than half of the structural weight of commercial aircraft consist of aluminium alloys. Similarly, the latest generations of highspeed trains and ferries deliver optimal performance and energy-efficiency targets by innovative use of lightweight aluminium in numerous applications [15]. In the automotive segment, it is now being used for engine blocks, cylinder heads, pistons, brakes, wheels, suspension arms, knuckles, sub-frames, steerings, drivelines, heat shields, body closures and structures, crash management systems, heat exchangers etc. Apart from innovation in development of new high strength alloys (discussed earlier) and new applications, a significant amount of research is also focussed on enabling technologies for facilitating aluminium penetration such as hot forming (especially for 7xxx alloys which do not form well at room temperature), dissimilar metal joining (friction stir welding, adhesive bonding etc.), machining, materials modelling for better understanding of processing-alloy (micro)structure-product property correlations, product design and advanced surfaces and coatings.

3.2 Electric Vehicles Due to the advent of electric vehicles, aluminium usage in the auto-segment has received a further boost, especially for the rolled products and extrusions. BEVs (Battery Electric Vehicles) and HEVs (Hybrid Electric Vehicles) are expected to use more of rolled components and extrusions in comparison with ICE based vehicles [16]. Figure 7 shows the shifting product mix for aluminium components in electric

Fig. 7 Shifting aluminium product mix in electric vehicles [16]

Aluminium As a Structural Material

35

vehicles as compared to conventional usage of aluminium castings in IC engine based vehicles. Apart from the conventional applications of aluminium in the automotive vehicles, new applications specific to EVs have also started emerging especially in battery frames and casings, aluminium wires and cables and battery cooling systems. Most of the established automotive OEMs such as BMW, Audi, Porsche, Daimler, and Volvo and the new group of start-ups are approaching the design of battery enclosures based on Tesla’s aluminium-extrusion intensive skateboard design [17]. As EVs start moving from the existing luxury vehicle segment (Tesla Model S and X, Jaguar IPACE, Audi etron etc.) to mid-segment vehicles and SUVs, extrusion-based designs might give way to sheet-based design to cope with the larger volumes. Novelis has already showcased a completely sheet-based battery enclosure designed for a 90 kWh battery pack [18]. Simultaneously Constellium is working on developing higher strength extrusion alloys called HSA6 alloys with properties in excess of AA6111 sheets with targeted yield strengths exceeding 500 MPa. Constellium has also developed a novel cold plate technology called CALD (cold aluminium) cooling plate for efficient cooling of battery modules [17].

3.3 Energy Generation and Storage Aluminium is being used in solar thermal energy generation as parabolic reflectors for concentrating solar power and as collectors for heating solutions. Extruded aluminium frames are also used extensively in solar thermal and photovoltaic applications. It is also used to a lesser degree in wind energy applications in nacelle and other coverings, rotor hubs and structural components. Aluminium also finds usage in energy storage applications. It is used as the cathode collector in Lithium ion batteries which have become an integral part of our everyday lives due to their utility in portable devices such as mobile phones, laptops, and cameras. The advent of electric vehicles has further increased the focus on development of higher energy densities, faster charging times and weight reduction for lithium ion batteries. Another aluminiumbased battery system, aluminium-air battery has been developed and is now being commercialised by Israel based Phinergy systems [19]. The theoretical energy density of aluminium-air batteries of 8.1 kWh/kg far exceeds that of Li-ion batteries (0.63 Wh/kg). However, aluminium-air is a primary battery, i.e., non-rechargeable and depends on physical recycling of reaction products.

3.4 Energy Efficient Buildings Aluminium is widely used in building applications for its superior aesthetics, durability and recyclability. Aluminium is now utilised for a host of applications in building and construction and is the material of choice for curtain walling, window

36

S. Adhikari et al.

frames and other glazed structures. It is extensively used for rolling blinds, doors, exterior cladding and roofing, suspended ceilings, wall panels and partitions, heating and ventilation equipment, solar shading devices, light reflectors and complete prefabricated buildings. Structures like offshore living quarters, helicopter decks, scaffolding and ladders are also commonly made of aluminium. New research is being focussed on developing intelligent building envelopes contributing to energy efficiency and user comfort, developing intelligent multi-functional surface properties for aluminium building components, maximising the production of renewable energy (e.g. photovoltaics cells in shading devices and/ or thermal energy collector in roofing systems) from the building envelope leading to energy positive buildings etc.

3.5 Recycling One of aluminium’s advantages over its competitor materials is its suitability for repeated recycling with high recovery rates without loss of quality. Aluminium recycling offers clear energy and environmental benefits; it requires only around five percent of the energy use and emissions associated with primary production. However, the recycling industry faces technical challenges both in making further efficiency improvements to melting and purification systems and in ensuring a steady and reliable scrap stream. Pre-consumer scrap or production scrap is relatively easy to recycle since its quality and composition are usually known and the scrap material is often uncoated. Post-consumer scrap requires a lot more effort for collection as well as processing. The development of affordable sorting technologies for better separating aluminium scrap from the waste flow as well as potentially separating aluminium scrap into alloy groups is an essential prerequisite for recycling. More efficient, robust and sensitive technologies that are also cost effective (such as x-ray based, eddy current technologies, sensor-based or near-infrared sorting systems etc.) are being developed. Another key area of recent research is developing low-cost processes for melt purification to remove specific impurities like Mg, Fe, Pb, Li, Si, Ti, etc.

4 Industrial Capability The total aluminium production in India in FY 2019 was 3.68 Mt. Vedanta Limited is currently the largest aluminium producer in India with primary production at 1.959 Mt in FY 2019. Hindalco Industries produced 1.259 Mt while state owned Nalco produces 0.440 Mt [20]. Hindalco is the largest producer of aluminium flat rolled products while Jindal Aluminium is the largest producer of extrusions (Tables 1 and 2) [21]. Imports is a major concern for aluminium domestic players, and accounted for nearly 60% of the market at ~2.3 Mt (including scrap) in FY 2018–2019 [22]. While

Aluminium As a Structural Material Table 1 Major aluminium rolling companies in India [21]

37

Company name

Company capacity (tpa)

Plant locations

Hindalco Industries

282,000

Belur Hirakud

Plant capacity (tpa) 37,000 135,000

Mouda

20,000

Renukoot

53,000

Taloja

31,200

Balco

46,800

Korba

46, 800

Virgo Aluminium

45,000

Chandigarh

45,000

Metenere Limited

40,000

Damtal

40,000

India Foils Ltd. (IFL)

37,000

Kolkata

17,000

Paragon Industries

Heora

20,000

34,000

Roorkee

34,000

Nalco

31,000

Angul

31,000

Jindal Aluminium

25,000

Bangalore RMD

25,000

Table 2 Major aluminium extrusion companies in India [21] Company name

Company capacity (tpa)

Plant location

Plant capacity (tpa)

Jindal Aluminium

90,000

Bangalore

90,000

Hindalco Industries

49,000

Alupuram

14,000

Renukoot

35,000

Global Aluminium

44,500

Medak

44,500

Alom Extrusions

22,500

West Bengal Balasore

13,500

Sudal Industries

18,000

Nasik

18,000

Maan Aluminium

17,000

Dhar

17,000

Bhorukha Aluminium

15,000

Mysore

15,000

Century Extrusions

14,500

Kharagpur

14,500

Banco Aluminium

14,500

Baroda

14,500

9,000

the majority of imports are due to a lack of capacities, imports are also rising due to a lack of capabilities. The predominant flat rolled products being imported due to these factors are can-body stock, lithographic sheets, fin-stock (coated and uncoated), hard alloys etc. In the extrusion segment, premium quality anodised and coated profiles and

38

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free-machining alloys for automotive applications are mostly imported. In order to deter imports and increase self-reliance, domestic aluminium producers have planned for significant expansion plans for the next few years. Hindalco industries plans to invest $1.0–1.2 billion in its downstream product expansion over the next 5–6 years including India’s largest extrusion and recycling plant in Gujarat. The planned annual extrusion production capacity and recycling capability will be 150 kT and 300 kT respectively [23]. Most of the aluminium producers in India including Hindalco, Vedanta, Nalco and Jindal Aluminium have invested in building in-house research and development capabilities. Research on aluminium alloys is also carried out in laboratories such as Defence Metallurgical Research Laboratory (Hyderabad), Vikram Sarabhai Space Centre (Trivandrum), Jawaharlal Nehru Aluminium Research, Design and Development Centre (Nagpur), Aditya Birla Science and Technology Corporation (Taloja, near Mumbai), and academic institutions, most notably the IITs and the Indian Institute of Science, Bangalore. Several Indian industries which are consumers of aluminium semi-fabricated products (castings, sheets, extrusions, foils) such as Tata Motors, Mahindra, and Bajaj Auto as well as the global industry leaders such as Boeing and GE also conduct and influence research and development activities in aluminium alloys and applications. Although the Indian efforts have succeeded in making the country self-reliant in bauxite, pure aluminium and many commercial aluminium alloys, there is still a gap in the requirements of aluminium alloys and their products for the ‘Defence, Aerospace and Transportation’ sectors and the industrial preparedness to deliver them in size, quantity and certifiable quality. One of the major reasons for this gap between the demand and indigenous supply is a lack of technological preparedness, coupled with a lack of critical infrastructure in the Indian aluminium industries. A lack of infrastructure and investments by private aluminium players to bridge that gap in turn results from poor economies of scale (lower demand in India) in the niche market segments. A well-planned, organised and efficient methodology for collaboration among the Indian government and affiliated agencies, aluminium industries and academic institutions will be vital in promoting aluminium usage in India. In addition, education and training of skilled manpower for both academia and industry is of utmost importance.

5 Smart Manufacturing and Industry 4.0 Recent socio-economic conditions, coupled with advancements in technology (both cyber—IoT, Big Data, Artificial Intelligence and physical—additive manufacturing, automation, remote sensing) are disrupting the traditional business models and redefining how businesses will work in the future. Industry 4.0 introduces the concept of ‘smart factory’ in which computers and automation will come together in an entirely new way, assisted by smart sensors, internet of things, cloud computing, big data, machine learning and artificial intelligence. It can learn and control the process with very little input from human operators [14]. The aluminium industry is

Aluminium As a Structural Material

39

also changing from the conventional plant-based physical manufacturing systems to digital manufacturing. In primary aluminium production, digital twins are being created coupled with scientific models that can predict pot cell performance. Additionally, rapid and automated sensors and measurement systems are being created that can provide continuous measurements of the pot, individual anode current measurements that could greatly reduce perfluorinated chemicals (PFCs) and emissions, and virtual control rooms that provide 24/7 monitoring and analysis of the data from multiple plants. For the aluminium downstream industry also, manufacturers are devising methods to adopt digitalisation and Industry 4.0 norms along with putting plants on a common platform of Industrial Internet of Things (IIoT) with Cloud based Data Computing and Analytics. Apart from this, one of the key developments has been in the area of through-process modelling or Integrated Computational Materials Engineering (ICME). Process and material knowhow in industrial fabrication and processing of semi-finished products such as aluminium sheets or extrusions was historically based on direct plant experience, described by empirical relations and based on laboratory testing methods. ICME is the integration of materials information across multiple length scales, captured in computational tools along with engineering product performance analysis and manufacturing process simulations, which can be used for accelerating the design and industrial deployment of new materials. Over the past decade, ICME-based approach has been used for simulation of microstructures and related properties of aluminium sheets including DC ingot casting, pre-heating and homogenization, hot and cold rolling, final annealing and heat treatments [24].

6 Research and Development Needs The aluminium industry in India is continuously evolving based on the needs of the market. In mobility and infrastructure segments, it is mostly catching up with capabilities already existing in mature markets such as Europe, North America, Japan, Korea and China. Also, owing to new initiatives and policies of the Indian government, some India-specific solutions might also emerge mostly related to energy efficiency, power industry, packaging and transportation. At the same time, global dynamics are also pushing several breakthrough technology areas which will impact India in a big way. A list of some such disruptive technologies (which is an ever-evolving list) is as follows: • • • • • • •

Additive manufacturing Electric Vehicles High speed transportation Computational materials engineering Recycling and sorting technologies Lo-cost melt purification Dross management

40

• • • • • •

S. Adhikari et al.

Advanced joining technologies Aluminium in energy storage Advanced data analytics Autonomous vehicles Automation and robotics Artificial intelligence and machine learning

New focus areas for research and development keep on emerging on the basis of manufacturing capabilities and challenges, business requirements and strategy, market dynamics and new technological innovations. A list of such short, medium and long-term R&D needs in the areas of casting, solidification and recycling, new process development, value added products and new application development and fabrication technologies is presented in Table 3.

7 Conclusions The aluminium industry is using the increased regulatory requirements for CO2 emissions reduction as an opportunity for pushing aluminium growth. Aluminium producers are devising new strategies to improve process efficiencies, and also developing new alloys and applications with improved functionalities to make aluminium adoption attractive and cost-efficient. The aluminium industry globally as well as in India is making a focussed and sustained effort not only for reducing its own environmental impact but also in coming up with solutions that can reduce the environmental impact of urbanisation. It is playing a vital role in light-weighting, electric mobility, renewable energy, energy storage, energy efficient buildings simultaneously bringing along the benefits of recyclability; all these make it a key material towards sustainable world. Aluminium consumption in India will also be propelled by government initiatives like Make in India, Smart Cities, Electric mobility, Housing for all, rural electrification and freight corridors. Ensuring this necessitates continued R&D in India for process improvements and new product and application development in aluminium along with shifting focus towards new enabling technologies such as AI & advanced data analytics, computational materials engineering and additive manufacturing which could have a significant impact on the aluminium industry.

• High temperature low sag conductors • Improved anodizing quality sheets • Extrusions for building and construction • Aluminium bus body, commercial vehicles, bulker, oil tanker etc

• Improved formability of 3xxx, 5xxx • Predictive modelling of forming • Develop advanced joining alloys behaviour and limits for hard alloys technologies such as friction-stir • Fusion welding of high-strength • Machining processes to maximise welding and adhesive bonding 6xxx alloys productivity, reduce environmental • New surface functionalities such as • Sensors for data collection, impact and ensure dimensional tailored friction, self-cleaning digitilisation of existing data • Understanding microstructure stability • Low cost innovative Cr-free evolution along the process chain conversion treatment of aluminium through ICME • ICME based optimization of homogenization and annealing

New products and applications

Enabling fabrication technologies

• High machinability extrusions preferably Pb-free • Capabilities for processing high strength 2xxx, 7xxx alloys • Capabilities in auto body sheets, railway wagons

• AL-Li, Al-Sc alloys, alloys for higher strength, modulus • Aluminium in high speed trains, metro rail • Aluminium in electric vehicles • Aluminium in energy storage (Li-ion, Al-air batteries)

• New continuous casting technologies (e.g. Alcoa’s Micromill) • New dross processing technologies • Cold cladding technologies • Additive manufacturing of aluminium

• Reduction in peripheral coarse graining of extrusions • Improved coating methods for corrosion protection

• Extrusion billet quality improvement • Slab/strip casting technologies to better control surface, texture and reduce segregation

Long term (>3 years)

New/Improved processes

Medium term (1–3 years)

• Techniques to selectively remove impurities such as Fe, Mg, Si, Pb, and Ti • Effect of recycling impurities on solidification process—models to predict and control microstructure and properties

Short term (0–1 years)

Casting, solidification and recycling • Improving DC Slab quality—defect • Defect-free casting of new free casting of 3xxx and 5xxx alloys alloys—2xxx and 7xxx • Improved scrap sorting technologies • Improve melt quality—sensors for for recycling real-time chemical analysis • Dross reduction and aluminium recovery from white/black dross

Focus area

Table 3 Short, medium and long-term R&D focus areas for the Indian Aluminium Industry

Aluminium As a Structural Material 41

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Acknowledgements The authors would like to thank Prof. K. A. Padmanabhan, FNAE, FIIM, FIASc, FNASc, FIMMM, Professor of Eminence (Honorary), Anna University, for his critical reading and suggestions.

References 1. I.J. Polmear, Light Alloys—From Traditional Alloys to Nanocrystals, 4th edn. (s.I. Elsevier, 2005) 2. https://www.statista.com/statistics/863681/global-aluminium-consumption/. [Online; Last acccessed: 26/11/2020] 3. https://engineering-machining.com/2016/01/grouth-of-the-global-aluminium-consumption/. [Online] 4. https://www.atkearney.fr/metals-mining/article?/a/how-gcc-smelters-can-continue-growingprofitably. [Online; Last acccessed: 26/11/2020] 5. https://www.crugroup.com/. [Online; Last acccessed: 26/11/2020] 6. Draft Strategy on Aluminium Resource Efficiency by NITI Aayog (2018) 7. https://aluminiuminsider.com/aluminium-alloys-automotive-industry-handy-guide/. [Online; Last acccessed: 26/11/2020] 8. Cosmetic Corrosion of Aluminium Automotive CLosure Sheet. (Scamans, Geoff., Light Metals Age, 2014), pp. 6–12 9. V. Mann, A. Krokhin, A. Alabin, D. Fokin, S. Valchuk, New Al-Mg-Sc Alloys for Shipbuilding and Marine Applications (Light Metals Age, 2019), p. 29 10. M. Niedzinski, The Evolution of Constellium Al-Li Alloys for Space Launch and Crew Module Applications (Light Metals Age, 2019) 11. https://aluminiuminsider.com/aluminium-lithium-alloys-fight-back/. [Online; Last acccessed: 26/11/2020] 12. S. Waszkiewicz, M. Ozog, L. Wodzinski, P. Uliasz, Development of Innovative Aluminium Alloys for Production of Overhead Electrical Conductors (2015), pp. 20–26 13. V.Kh. Mann, A. Yu Krokhin, I.A. Matveeva, G.I. Raab, M. Yu Murashkin, R.Z. Valiev, Nanostructured Wire Rod Research and Development in Russia. (Light Metals Age, 2014), pp. 26–29. 14. A. Gupta, B.Basu, Sustainable primary aluminium production: technology status and future opportunities. Trans. Indian Inst. Metals 72, 2135–2150 15. https://european-aluminium.eu/media/1649/european-aluminium-innovation-hub-mappingreport-v1.pdf. [Online; Last acccessed: 26/11/2020] 16. G. Wittbecker, Aluminium Market Outlook Trade Rises to Top of the Agenda (AEC Annual Meeting - Aluminium Extruders Council 2018) 17. G. Scamans, ELectric Vehicles Spike Demand for High Strength Aluminium Extrusions (2018), pp. 6–12 18. A. Svendsen, Novelis Becomes Development Partner for Automotive Aluminium (2019), pp. 6–9 19. http://www.phinergy.com/. [Online; Last acccessed: 26/11/2020] 20. https://www.alcircle.com/news/vedanta-becomes-the-largest-aluminium-producer-in-indiain-fy2019-contributing-about-53-of-total-production-45717. [Online; Last acccessed: 26/11/2020] 21. A. Hall, Hindalco—The Largest Aluminium Company in India Plans Massive Expansion (Light Metals Age, 2018)

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22. HIndalco Annual Report 2018-2019 23. https://aluminiuminsider.com/hindalco-inks-deal-with-indian-state-of-gujarat-to-build-newaluminium-extrusion-and-recycling-plants/. [Online; Last acccessed: 26/11/2020] 24. J. Hirsch, Advances in integrated computational materials engineering “ICME”, in 2012. 13th International Conference on Aluminium Alloys (ICAA13) eds. by A.D. Rollett, W.A. Cassada Hasso Weiland

Titanium and Magnesium as Structural Materials Amol A. Gokhale

1 Titanium: Introduction and Background Titanium and its alloys are known for their relatively low density, high corrosion resistance, ability to develop high strength, and good creep resistance up to about 550 °C. These characteristics have earned them their due place in air frames and aeroengines. Their usage in other sectors is limited to biomedical implants, chemical processing equipment, sports goods, and, to a small extent, armour. A large proportion of Ti-alloys are used as forgings, plates, sheets, tubes, and, to a small extent, castings [6]. The initial applications of titanium alloys in aerospace were in the compressor section of the aeroengine, where their high-temperature capability was primarily the reason for their selection. However, the introduction of Ti-alloys in the air frame of Boeing 787 saw a major shift in the material distribution in that application (Fig. 1). They replaced aluminium alloys in the air frame, in spite of their higher density. This was possibly because Boeing had decided to use CFRP (Carbon Fibre-Reinforced Polymers) in the air frames due to their higher strength-to-weight ratio and the fact that aluminium is not galvanically compatible with CFRPs [5]. Parts of the landing gear of Boeing 777 and 787 are now made of Ti-alloys, which were earlier made of high-strength steels, resulting in weight saving [6]. Table 1 shows the gradual increase in the titanium content used in the air frames of various Boeing and Airbus passenger aircraft. Future higher supersonic aircraft such as the Advanced Medium Combat Aircraft (AMCA) will perhaps see increased usage of titanium sheet components in nearengine locations due to service temperatures expected to be beyond the capability of currently used Al-alloys.

A. A. Gokhale (B) Department of Mechanical Engineering, IIT Bombay, Mumbai, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_3

45

46

A. A. Gokhale

Fig. 1 Usage of Ti-alloys in commercial airplanes [9]

Table 1 Distribution of various materials used in the air frame of passenger and fighter aircraft [9] Materials distribution (wt%) Material

Boeing [5]

Airbus [6, 7]

747

757

767

777

787

81

78

80

70

20

61

19

4

6

2

7

15

10 (Ti and steel)

14

13

12

14

11

10

Composites

1

3

3

11

50

22

53

Other

1

1

1

1

5

7

8

Aluminum Titanium Steel

A380

A350

6

The other application where titanium could partially replace nickel is the aeroengine, where titanium aluminide intermetallic alloys could replace Ni-based superalloys for High-Pressure Compressor (HPC) blades and Low-Pressure Turbine (LPT) Blades [6]. Some of these applications have already been realised in GE’s recent engines [2]. An area that holds promise is low-cost Ti-alloys, which can replace stainless steels in chemical industries, sports gear, etc. Effective recycling technologies and the use of cheaper alloying elements may pave the way for producing low-cost Ti-alloys. Similarly, the buy-to-fly ratio of Ti-alloy-based forgings remains very high at present, which effectively reduces its yield and increases machining scrap. Reducing the buy-to-fly ratio in Ti-alloy forgings depends on a combination of (a) more accurate non-destructive techniques which can be applied on curved surfaces, (b) better forging techniques which can produce more intricate geometries, and (c) more reliable fatigue-life prediction models [6].

Titanium and Magnesium as Structural Materials

47

Ti-based parts have been introduced in automobiles since the 1990s due to their high strength, low density, and high corrosion resistance [3]. These include motorcycle muffler, valve spring retainers, intake and exhaust valves, gear shift knob, etc. However, the sheet products currently made of steel are not expected to be replaced by Ti-alloys due to (a) development in Advanced High-Strength Steels which makes Ti-alloys less attractive and (b) high cost of Ti-alloys. Another related challenge in introducing Ti-alloys in automotive bodies is that many parts are welded and that Ti cannot be easily welded using conventional welding techniques and depends heavily on the more expensive electron beam welding technique.

2 Industrial Capability 2.1 Titanium Sponge With 593.5 Mt of ilmenite and 31.3 Mt of rutile, India has the third-largest deposits of titanium ores in the world [7]. However, it was only in 2012 that a 500 t Ti-sponge plant came into being under funding from ISRO based on DRDO Technology. This plant is hosted and operated by Kerala Minerals and Metals Limited, a state PSU. It uses ilmenite ore mined at the Chavara coast, converted in stages to TiO2 and then to aerospace grade TiCl4 . The technology is based on time-tested Kroll’s process which is basically a magnesiothermic reduction process. It may be mentioned that the indigenous Ti-sponge has been certified by airworthiness agencies. The outstanding issues with respect to sponges are high price (about $22 per kg) compared to the international price (about $9 per kg in 2019). This is partly related to the facts that (a) grades other than the top grade, which are not suitable for aerospace use, are difficult to sell, thus adding to the overall price of the sponge and (b) recycling of magnesium which is used as the reductant in Kroll’s process has not yet taken place. There have been several instances where state governments with foreign collaborations have expressed interest in exploiting ilmenite resources of their states to produce Ti-sponge, but none has materialised.

2.2 Downstream Processing Mishra Dhatu Nigam (Midhani), a Defence PSU, has most facilities such as Vacuum Arc Remelting (for making ingots out of Ti-sponge), Forging press (for break down and shape forging), rolling mill (for flat products), and heat treatment required to produce various mill forms mentioned in the introduction. The installed capacity of Midhani is 300 t mill products, which is projected to increase to 500 t initially, but can go up to 1000 tpa. Apart from Midhani, BHPV, Visakhapatnam now known as

48

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BHEL HPVP has large-scale facilities for titanium ingot downstream processing. There are other companies that cover part of the downstream processing value chain. For example, Bharat Forge has forging and ring rolling facilities and capabilities for titanium; NFC has been manufacturing extruded titanium/titanium alloy tubes; TEAM (Titanium Equipment and Anode Manufacturing Co.), TiTan (titanium & tantalum products), Alfa Laval India, etc. have been manufacturing a variety of titanium products over the last three decades.

3 Trends and Drivers 3.1 Users of Titanium and Alloys The following are the known users of titanium and its alloys in India: Indian Space Research Organisation (ISRO), HAL, Defence Research and Development Organisation (DRDO), Brahmos Aerospace Pvt. Limited (an Indo-Russian Joint Venture), and Midhani, all being for aerospace structural and engine applications.

3.2 Type of Structural Materials, Processes, and Functionalities of Interest Combat aircraft programmes of the country typically use alloys in bar, plate, sheet, tube, wire, and forging forms, involving various processing operations such as melting, casting, forging, extrusion, rolling, ring rolling, cladding, heat treatment, fabrication, and machining. The most common alloys used are Ti-6Al-4 V (normal and ELI, i.e. extra low interstitials grade), Ti-5Al-2.5Sn-ELI, VT-14 (Ti-5.4Al-3Mo1 V), Ti-3Al-2.5 V, and Ti-15 V-3Al-Sn-3Cr alloy. Another area of interest is Ti-alloys for demanding environments, such as for hypersonic thermal protection systems and for impact-absorbing applications. Applications of electron-beam-welded hemispherical caps to make air bottles (pressure vessels) are being realised in ISRO (see Fig. 2) [4]. Applications of smart alloys based on Ti such as Nitinol have been realised in hydraulic couplings used in fighter aircraft. Programmes aimed at higher supersonic aircraft will further increase the proportion of titanium used in the air frame.

3.3 Immediate Term (Up to 2020) The current indigenous efforts of manufacture of aeroengine discs for the licensed production of an aeroengine, using a near-isothermal forging process, will culminate

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Fig. 2 Forged and machined hemisphere (inset: pressure vessel made out of hemispheres) [4]

during this period. Also, the industrial capability to make beta alloy forgings for landing gear and beta alloy sheets for higher supersonic fighters will mature during the same period. Apart from industrial capability development, the airworthiness certification is also expected to be completed. In the near future, one can expect the launch of the development of newer Ti-alloys equivalent to Ti-5553 for landing gear applications in place of Ti-10-2-3 alloy. In Ti-5553, the rate of change of β volume fraction with temperature (below β transus) is low, making it easier to control it within 5–10% for the purpose of optimising between creep and fatigue resistance. Similarly, the development of Ti-alloy sheets of compositions equivalent to Beta21S is likely to reach industrial level production to cater to higher supersonic aircraft skin as well as hypersonic applications. Liquid hydrogen tanks made of EB-welded Ti-alloy are suitable for cryogenic engines for satellite launch vehicles. Thus, complete transition to cryogenic propulsion will drive up the requirement of super alpha Ti-alloys, which have good properties at cryogenic temperatures (20 K). In terms of processing, hot isostatic pressing of powder Tialloys, isothermal forging for complex products will see further growth, apart from EB welding. The other generic areas which will gain importance in the near future are production technologies that are cost-competitive for commercial uses, products with a higher buy-to-fly ratio to reduce scraps, and green processing technologies due to stringent environmental regulations.

3.4 Medium Term (2020–2025) Beyond the immediate term, which will also spill over to the medium term, developments in Super Plastic Forming (SPF) and Diffusion Bonding (DB) are expected to reach a level where component trials and evaluations may take place. SPF/DB is not a new concept and much research work has been published [8], especially

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Fig. 3 SPF and SPF/DB applications on F-15E [10]

for Ti-alloys (Fig. 3). However, no significant component development activities are reported. Given the promise of fabrication of complex parts in a single integral process, more efforts in this area are likely to be made. Apart from this, improving the balance of properties such as strength and fracture toughness for beta alloys and improving the balance between strength, creep resistance, and LCF resistance for near-α alloys for the disc will be pursued.

3.5 Long Term (Beyond 2025) The following areas are likely to pick up in the long term. More products based on shape memory alloys will penetrate the market in biomedical applications as well as in aerospace applications. Since the higher supersonic aircraft being planned in the country are much larger than the current fighter aircraft, more quantities of shape memory alloy hydraulic couplings are expected to be produced. There is work showing that Ti-alloy components can be made by additive manufacturing (Fig. 4). However, the dynamic properties of such products have not been adequately demonstrated. Also, questions that remain to be answered are related to the type certification of such products. In the long term, the currently ongoing efforts in understanding the mechanical and corrosion behaviour of additively manufactured Ti-alloy components will reach a point of maturity.

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Fig. 4 Titanium Laser Deposited Rib Section (Campbell 2006)

In the long term, we should see the batch scale of Ti-sponge process increase from the current 4 t per batch to 8 t per batch. This should also reduce the sponge price and make it competitive with the international price.

4 Technology/Infrastructure Gaps There remain certain crucial gaps in indigenous technologies and capabilities. First, there are no large-scale forging presses in India: this is hindering the application of technology for forging aeroengine discs of Kaveri engine class. The crucial challenge here is to generate enough work to keep the press engaged to justify the purchase. Larger-width rolling mills are required to produce plates of adequate width for ISRO as well as Brahmos programmes. Investment casting of Ti-alloys is not yet fully developed within the country, although PC castings, Lucknow, is known to have initiated work in this area. Midhani as well as HAL Koraput have some experience but there are perhaps no continuous orders for such items. If titanium aluminides are to replace Ni-based superalloys, they would be used as investment castings for which this technology is required. There is also a need for a hot isostatic press facility to go along with investment castings to close the casting porosity and achieve properties comparable to forged products. The technology of additive manufacturing has not reached a maturity level for titanium alloys, possibly due to the reactive nature of titanium and the need to

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have a protective atmosphere during manufacturing. Also, extensive evaluation and certification of additively manufactured products are a must. In general, titanium aerospace products require extensive fatigue and creep testing. These tests are time taking. Apart from AMTL in Hyderabad, there is no other place that houses a collection of facilities to evaluate mechanical and corrosion properties of aeronautical materials. Such an infrastructure is required for R&D as well as for routine certification and inspection of items. In the medium term, the technology of hot isostatic pressing for Ti-components needs to be developed. Further, there is a need to develop wear-resistant coatings for Ti-alloys, while for certain applications, cladding technologies are also required.

5 Market Growth Areas 5.1 Immediate Term (Up to 2020) Given the current low usage of Ti-alloys in the country, all possible sectors of application such as defence, aerospace, and chemical processing equipment can be considered as growth areas. Biomedical applications are also an emerging field and, with adequate push, should grow substantially. Internationally, applications in surgical implements and implants, such as hip balls and sockets (joint replacement) and dental implants, are already emerging. This aspect has been extensively covered in the Biomaterials chapter.

5.2 Medium Term (2020–2025) Growth can be expected in the medium term for various types of high-strength Ti fasteners including blind fasteners for aircraft applications. In the same period, automobile applications, especially for low-cost high-strength Ti-alloys, will emerge.

5.3 Long Term (Beyond 2025) In the long term, the space, defence, biomedical, automotive, and sports sectors will continue to grow. If and when indigenous development of aeroengines becomes successful, and as aeroengine production increases, there will be a corresponding increase in demand for Ti-alloys. Similarly, when the medium combat aircraft reaches the production stage, there will be an increase in demand for air frame alloys.

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6 Research and Development Needs In a recent review, Banerjee and Williams [1] have described several topics concerning the physical metallurgy (specially crystallographic aspects of beta to alpha phase transformation) and the mechanical behaviour of Ti-alloys which are not fully understood. These gaps in the knowledge need to be filled if modelling and simulation-based accelerated development of alloys are to become a reality. Among the vast range of possible research areas, there are some which have a direct relevance with respect to known and future applications in the country.

6.1 Immediate Term (Up to 2020) In the near term, research and development efforts need to focus on the following areas: • ATI 425 is an alloy that contains lower Al and V than Ti-6Al-4 V, addition of Fe and higher amounts of O for good combinations of ductility and strength. Besides, it possesses good cold and hot formability. It is melted using single plasma melt technology (not available in India yet), which eliminates inclusions and provides better chemistry control [6]. Moreover, this alloy was developed to reduce the cost of fabricating components. • ATI 425 possesses good cold and hot formability; fatigue strength and FCGR characterisation of newer Ti-alloys. • Formability studies of newer Ti-alloys such as Beta21S sheets. • Recycling of solid Ti-alloy scrap, Flow Forming, and High-temperature Ti-alloys. • Identification and development of alternative /new materials for replacing existing materials to reduce weight and to have superior performance. • Investment casting of Ti-alloy components to near-net shape. • Master alloys (for V, Mo, etc.). Currently, all Ti-alloys made in the country use imported master alloys as raw materials.

6.2 Medium Term (2020–2025) In the medium term, the following areas would be important from a research point of view: • High-temperature strength and creep studies of newer Ti-alloys. • Additive manufacturing. • Welding consumables.

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6.3 Long term (Beyond 2025) In the long term, R&D in Ti-matrix composites for bling (bladed ring) applications and in aluminides for aeroengines will be required.

7 Summary India is advantageously positioned in raw materials, R&D infrastructure, and manufacturing capabilities to produce Ti metal, alloys, and products to meet indigenous requirements in the strategic sector. In spite of the anticipated growth in the defence and aerospace requirements in the next two to three decades, the overall consumption of Ti and its alloys in India will remain low to moderate, which raises concerns about it being economically competitive internationally. This requires strategic investments and capability enhancement, backed by continued R&D, based on comprehensive analysis and forecasts of the global markets.

8 Magnesium: Introduction Magnesium with a density of 1.8 g/cc is one of the lightest metals. The principal use of magnesium metal is not in structural alloys, but as an alloying element in aluminium. Its other important use is as a reductant in the Kroll Process to produce titanium metal from titanium tetrachloride. At the component level, it is used in nonstructural casings in aerospace (sand castings, pressure die castings) and in electronic equipment covers (laptop, mobile phones, etc.) in the form of mill forms like sheets. While defence equipment and nuclear reactor materials also consume magnesium, there is sustained effort in using magnesium either in castings in automotive engines or in various mill forms in other areas as well. The current demand for magnesium in India is estimated to be about 1000 tpa, of which 60% accounts for aluminium alloy, 25% for the aerospace and defence sector, and the balance for casting and miscellaneous industries. Currently, there is hardly any magnesium metal production in the country; hence, the entire magnesium metal requirement is met through imports. As a result, India is importing about 800 Mt per annum magnesium metal for use in the production of titanium/zirconium sponges. The principal mineral which is found in India is magnesite. Its known reserves stand at 13 Mt by 2015 and probable reserves at about 7 Mt. In addition, magnesite resources are estimated to be about 307 Mt. About 276, 000 t of magnesite was mined in India in 2014–2015.

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9 Industrial Capability 9.1 Magnesium Metal and Castings Southern Magnesium and Chemicals Limited (SMCL), Andhra Pradesh, is the only known company to have produced magnesium metal, in a joint venture with the Andhra Pradesh Industrial Development Corporation. Their technology was based on the Pidgeon process, indigenised at laboratory scale at the National Metallurgical Laboratory. The pilot plant set up by SMCL at NML was of a capacity of 200 tpa. The company then carried out necessary alterations and additions and enhanced the capacity to 600 tpa. Commercial production commenced in 1990, as they became the first and only company in India to commercially produce magnesium metal. However, due to unfavourable market conditions, the company had to stop production and currently manufactures magnesium chips, turnings, granules, and powders [12]. Defence Metallurgical Research Laboratory (DMRL), Hyderabad, was operating a pilot plant to recycle magnesium chloride produced in the Kroll process, the metal being produced by fused salt electrolysis process both in monopolar and advanced multipolar cells in pilot plant scale. However, the plant was closed around 2003. Sea water/sea bitterns is also a major source of magnesium. Historically, fused salt electrolysis of anhydrous MgCl2 had been contributing to about 50% of world magnesium production. In India, CECRI has done a considerable amount of R& D on the fused salt electrolysis process. TMML (Tamilnadu Magnesium and Marine Chemicals Ltd) attempted to implement CECRI monopolar electrolysis process on an industrial scale. However, these operations did not last long due to a poor commercial outlook. Shaped castings are produced at HAL Foundry and Forge, Exclusive Magnesium Hyderabad, Hindustan Magnesium Co. Hyderabad, and a few other pressure die casters around the country. Efforts are now on by Kerala Minerals and Metals Limited as well as Nuclear Fuel Complex to establish plants in collaboration with DMRL Hyderabad for fused salt electrolysis of MgCl2 byproduct to produce magnesium metal.

9.2 Downstream Processing To the best of knowledge, there is no significant industrial activity to produce wrought products from magnesium alloys. There are no known large-scale applications of wrought mill products for magnesium alloys in India.

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10 Trends and Drivers Alloy thin-wall castings for components such as gear box casings, compressor casings, antenna housing, bearing blocks, and racks for electronic components are used in the aerospace sector. The alloys of interest in this area are AZ91C, AZ31B, RZ5, MSRB, Elektron 21 (Eq. 21), Mg-Zr-Nd alloys, and AZ92, ZK30, ZE41, WE54, and WE43. Alloys of the AZ series are easily produced by the Indian industries. However, alloys of the WE and ZK series are not produced from primary metals in India. Many alloys are produced using master alloys imported from Russia. The database on the usage of magnesium sheets by the electronics industry is poor, and more data collection is required in this area.

11 Research and Development Needs for Mg The areas in which R&D is required are as follows: Magnesium extraction by the Pidgeon process is known to be an energy-intensive process. NML has been working on an alternative process (Magnatherm Process), which promises to reduce the overall energy consumption. High-temperature properties including creep are in particular relevant to aerospace components. If Mg alloys are to succeed as body material in automobiles, their formability must be completely understood. Since corrosion continues to be the major hindrance to large-scale applications of Mg alloys, the development of corrosionresistant alloys and the development of reliable protective coatings continue to be the areas of prime importance. Also, Mg is currently not superior to either Al-alloys or CFRPs in terms of their weight-compensated properties. Hence, any significant use of Mg alloys for structural applications will depend on developing properties exceeding specific properties of these baseline materials.

12 Summary There is an urgent need to establish fused-salt electrolysis-based Mg extraction to make the production of Zr and Ti closed-loop processes. Melting practices suitable for making castings out of more exotic high-temperature alloys need to be established. Similarly, safer melting practices and effective coatings need to be developed to increase the use of Mg alloys in industrial applications. Acknowledgements This article is based on feedback received from some of the agencies which use Ti-alloys. Dr. V Gopalakrishna (BAPL), Dr. PV Venkitakrishnan (VSSC), and Dr. ChRVS Nagesh (DMRL) are gratefully acknowledged for the information provided.

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This article is based on feedback received from some of the agencies which use Mg alloys. Dr. V Gopalakrishna (BAPL), Dr. PV Venkitakrishnan (VSSC), Shri VP Deep Kumar (ADA), and Dr. ChRVSNagesh (DMRL) are gratefully acknowledged for the information provided.

References 1. D. Banerjee, J.C. Williams, Jr, Acta Mater. 61, 844–879 (2013). https://doi.org/10.1016/j.act amat.2012.10.043 2. B.P. Bewlay, S. Nag, A. Suzuki, M.J. Weimer, TiAl alloys in commercial aircraft engines. Mater. High Temp. 33(4–5), 549–559 (2016). https://doi.org/10.1080/09603409.2016.1183068 3. K. Faller, F.H. (Sam) Froes, Chapter on Titanium in Automobiles, Materials and Science in Sports, eds. by E.H. (Sam) Froes, S.J. Haake (TMS Publishers, Warrandale, PA, 2001), pp. 47–56 4. R.K.V. Gupta, A. Kumar, A.R. Chauthai, P. Ramkumar, Materials Science Forum (Trans. Tech. Publishers, Switzerland, 2015), pp. 3–6. https://doi.org/10.4028/www.scientific.net/MSF.830831.3 5. E. Hakansson, Galvanic Corrosion of Aluminum/Carbon Composite Systems (2016), Electronic Theses and Dissertations, p. 1120. https://digitalcommons.du.edu/etd/1120 6. G. Lutjering, J.C. Williams, Jr, Titanium, 2nd edn. (Springer Verlag, Berlin Heidelberg, 2007) 7. C.R.V.S. Nagesh, G.V.S. Brahmendra Kumar, B. Saha, A.A. Gokhale, N. Eswara Prasad, R.J.H. Wanhill (eds.), Aerospace Materials and Material Technologies, Indian Institute of Metals Series (Springer Science + Business Media, Singapore, 2017). https://doi.org/10.1007/978981-10-2134-3_4 8. K.A. Padmanabhan, S.B. Prabu, R.R. Mulyukov, A. Nazarov, R.M. Imayev, S.G. Chowdhury, Superplasticity: Common Basis for a Near-Ubiquitous Phenomenon (Springer, Berlin, 2018). https://doi.org/10.1007/978-3-642-31957-0 9. K.K. Sankaran, R.S. Mishra, Metallurgy and Design of Alloys with Hierarchical Microstructures (Elsevier Publishers, Amsterdam, 2017), p. p269 10. L. Hefti, Advances in manufacturing superplastically formed and diffusion bonded components. Materials Science Forum 447–448, 177–182. Online: 2004–02–15ISSN: 1662–9752. https:// doi.org/10.4028/www.scientific.net/MSF.447-448.177 11. IBM, Indian Minerals Year Book 2015 (Part III Mineral reviews), 54th edn. (Indian Bureau of Mines, Nagpur, 2017) 12. SMCL (2019). http://www.southernmagnesium.com/index.html. Accessed 27 May 2019

Structural Materials in Nuclear Energy Sector G. K. Dey

1 Trends and Drivers Nuclear energy sector involving commercial scale production of nuclear power and its use critically depends on ready availability of three types of special materials namely compounds/metal/alloy of natural/enriched uranium as fuel, heavy water as moderator/coolant (in case of pressurised heavy water reactors (PHWR)) and finally a whole range of structural materials (alloys/compounds) forming the core of nuclear power reactor and surroundings. Indigenous development and availability of these special structural materials of stringent specifications is the subject matter of present paper. In this context it is appropriate to mention that uninterrupted performance of any given system not only makes the process economically viable but also helps in proper utilization of the available resources. At the same time, running of an operational system with minimum ‘down-time’ is keyed to improved materials performance which is in turn directly related to stringent specifications of various metallurgical parameters like composition, microstructure, texture and defect density. In addition, one of the major constraints in the development of critical high performance alloys, as required in nuclear energy sector has been the lack of international cooperation in terms of knowledge-sharing due to existing embargos. This has prompted the Indian materials scientists to rise to the occasion and develop indigenous technologies to synthesize various alloys with highly stringent specifications. Scientists of the Department of Atomic Energy (DAE) have contributed significantly to this pursuit. The indigenous material development endeavour has been facilitated by the knowledge-base created by research and experience gained over the years. This has not only helped in tiding over the adverse situation created by embargos but also taken India closer to world leadership in the domain of materials development. The

G. K. Dey (B) Materials Group, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_4

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methods of production adopted have all the necessary environmental clearances. The emphasis on self-reliance in this area will continue in the future.

2 Industrial Availability Self reliance in structural materials for the nuclear energy sector in India comes from the functioning of industrial units like Nuclear Fuel Complex (NFC) (internals, fuels for various types of reactors), Uranium Corporation of India Limited (UCIL) (uranium mining and extraction from Indian resources is done by this unit), Indian Rare Earths Limited (IREL) (mining and separation of seven beach sand minerals (BSM), separation of rare earths and radioactive component from monazite, one of the BSMs) and Atomic Minerals Directorate for Exploration and Research (AMDER) with the latter being involved in exploration activities. This is besides other industrial units of Department of Atomic Energy (DAE) like Heavy Water Board (HWB), Board of Research in Isotope Technology (BRIT) and Electronics Corporation of India Limited (ECIL). Private sector participation is through companies like L & T, Walchandnagar etc. Companies like Bharat Heavy Electricals Limited (BHEL) are involved in the manufacture of turbine and generator for nuclear power plants. The country today is completely self-reliant in construction of Nuclear Power Plants based on PHWR Technology.

3 Market Growth Though many new power plant projects based on indigenous PHWR technology are already in operation and more have been sanctioned, reactors based on Russian technology have also started contributing to power generation. French and American technology may contribute to the nuclear power generation in the country in the future. Besides the thermal reactors, the country also has a fast breeder reactor programme with a beginning made with the Fast Breeder Test Reactor (FBTR). This is being followed by the Prototype Fast Breeder Reactor (PFBR) and other advanced reactors.

4 R & D on Structural Materials DAE has a very strong research-base spread across the country through its research laboratories like Bhabha Atomic Research Centre (BARC), Indira Gandhi Centre for Atomic Research (IGCAR), Raja Ramanna Centre for Atomic Research (RRCAT), AMDER and Variable Energy Cyclotron Centre (VECC). These have been involved

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in different aspects of materials development. The in-depth information for exploration of minerals in the earth crust, mining of these, mineral beneficiation of the ores, different types of extractive metallurgy techniques and purification techniques already exists in the department. The work done in the aforementioned laboratories has led to successful development of flow sheets for extraction/production of many of the elements required as components of structural materials by the nuclear power generation programme and other applications from indigenous resources. In this sector, one is often faced with the situation of indigenous development of alloys which have not been produced earlier. It may be noted that such alloys need not be new alloys. New alloys for a particular application in these critical areas have to meet many codal requirements and have to undergo many acceptance tests and hence have to undergo short term and long term testing which may require a very long time. Indigenous production of an existing tested and established bench mark alloy starting from Indian ore using the Indian processing route in many cases has been a formidable task in the beginning. However, these challenges have been successfully overcome. In the nuclear energy sector, it has been difficult to get processing equipment from other countries. Hence, advanced processing techniques, namely, vacuum melting, electron beam and plasma processing, reaction sintering have all been developed indigenously and deployed. Even the processing equipment have been designed and fabricated in-house. The combinations of hydro-, pyro- and electro- metallurgy have been skilfully used to extract metals from even lean resources. Based on such above mentioned R & D efforts, large scale manufacturing-flow sheets have been developed for different products in their final fabricated shapes either by NFC or by collaborative efforts between NFC and Mishra Dhatu Nigam (MIDHANI)—an unit of Ministry of Defense.

5 Production of Structural Materials Following is a flavour of work carried out by various units of DAE on production of structural materials from indigenous raw materials. The materials described here need not be load bearing members but may be finding applications in the reactor or other production facilities like heavy water plants. Depending upon the place of use the required properties in the alloys will change. Some of the items like shape memory alloys have been developed for use by other departments. The contents are not all inclusive and the effort is to give a flavour of the spectrum of materials and the nature of activities involved.

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5.1 Boron and Boron Based Ceramic Materials Boron carbide (B4 C) is a wonderful ceramic with many attractive properties like low density (2.52 gm·cm−3 ), high hardness (>30 GPa), high melting point (2450 °C), high elastic modulus (448 GPa), high neutron absorption cross-Section (600 barns) etc. These properties make B4 C particularly suitable for critical areas, such as nuclear, defence and space [1]. It also has thermoelectric properties and is a P-type semiconductor [1, 2]. Boron carbide is considered a candidate material for wear resistant components, polishing media, aerospace materials, light-weight armours, control rods and shielding materials in nuclear reactors [1–3]. As boron undergoes (n, alpha) reaction, it is also used as neutron detector in nuclear reactors due to its ability to absorb neutrons without forming long lived radionuclides [4]. Neutron absorption capacity of boron carbide can be increased by enriching B10 isotope. Composite materials containing B4 C with good thermal conductivity and thermal shock resistance are found suitable as first wall material of nuclear fusion reactors [5] as well as potential inert matrix for actinide burning [6]. B4 C is also used for treatment of cancer by neutron capture therapy [7] and has been used in light weight ballistic resistant jacket [8]. Recently, boron carbide–carbon nanomaterial composites have been developed with high fracture toughness [9–11]. Borides are important materials for high temperature applications. Titanium diboride (TiB2 ) is one of the candidate materials for high temperature structural applications and also for control rod elements in high temperature nuclear reactors. Extensive studies have been carried out on the synthesis and property evaluation of TiB2, HfB2, CrB2 and their composites [12–15]. Boron is very reactive in pure form and this creates many difficulties in preparing high purity boron. Since it is very difficult to pulverize due to its high hardness, any process of its extraction where grinding or crushing results in its contamination from the material of the equipment. Because of these difficulties, a electrochemical process of extraction has been adopted [16]. Coating of natural and enriched boron on aluminium as well as stainless steel have been carried out by dip coating method from fine suspension of boron in an organic medium. These coated elements have been used as sensors in neutron counters for measurement of neutron flux in various reactors [17]. Boral is a composite made up of boron carbide and aluminium, where aluminium provides the bonding between the particles. This material is fabricated by powder metallurgy route. Boral sheets produced in BARC [18] can be used in reactors for neutron shielding in beam holes and other locations. Bocarsil is a composite of silicon rubber, using boron carbide as the filler material. Silicon rubber was specially chosen for its longer shelf life. Bocarsil sheets are used as neutron shield in online fuelling machines of power reactors, for storage of nuclear materials and also in nuclear instrumentation. Poly-boron is a composite, made up of boron compound in High Density Poly Ethylene (HDPE) matrix. For neutron shielding of surrounding instruments using various radioactive isotopes, composites with boron content of less than 10% are also useful [19].

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5.2 Molybdenum Based Alloys The occurrence of molybdenum bearing minerals is rather scarce in the country and it occurs with titanium, copper, lead and zinc ores. Some estimates of the resources of molybdenum ore in the country have been made [20]. The extraction of molybdenum from primary and secondary resources at laboratory scale has been developed [21, 22]. The technology for molybdenum metal powder produced by hydrogen reduction of molybdenum trioxide was reported by BARC [22, 23]. The molten salt electrometallurgical processes for producing pure molybdenum from its oxides and carbides are also reported earlier [24–27]. Molybdenum bearing alloys such as TZM (Mo-0.5Ti-0.1Zr-0.02C) and Mo-30 W are suitable for high temperature nuclear reactor programme as carried out at BARC [28–30]. The work on developing high temperature oxidation resistant Mo-Si-Ti based alloys [31, 32] is being pursued at BARC.

5.3 Zirconium Based Alloys Zirconium and its alloys find application in many places, particularly in PHWRs. These in the form of Zircaloys are used for making fuel clads, and other components for the fuel bundle. Zirconium based alloys are used for making pressure tubes; earlier Zircaloy 2 was being used which were subsequently replaced by Zr-2.5Nb alloys. The calendria tubes made of zircaloy 4 are presently being used. The garter spring is made of Zr 2.5 Nb 0.5Cu alloys. The process for making zirconium from zircon coming from the beach sand was developed indigenously in BARC. Subsequently this was scaled up in NFC for tonnage scale production in NFC. Besides the mineral dressing, the extractive metallurgy of zirconium has been well studied by the Indian scientists [33]. This helped in creating the flow sheet for zirconium metal production. Subsequently the physical metallurgy of zirconium and zirconium based alloys has been studied. Indian scientists have studied all possible phase transformations in zirconium based alloys [34]. These studies have been carried out not just under thermal activation but some of these also under stress and radiation environment. Establishing irradiation stability of a material going inside a reactor is very important. Since doing such studies in neutron environment in a reactor is difficult, often proxy ion irradiation using protons is done [35]. Mechanical metallurgy of zirconium has been also studied. This has facilitated very good structure property correlation and creation of deformation maps of the different alloys. The development of texture during hot and cold deformation was also examined by the Indian scientist in great detail. Some glimpses of these very in depth studies are given in the following sections: Texture studies: Zirconium because of its hexagonal crystal structure, exhibits significant anisotropy in plastic deformation and consequently develops strong texture during the processing (such as hot and cold working and intermediate

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annealing) of components [36, 37]. The crystallographic texture so developed will determine the service performance of the components and hence understanding the texture development during the manufacturing is of crucial importance motivating several studies [38–51]. The texture development is a function of deformation conditions [38–40], annealing parameters [36, 47] and the composition and phase distribution of the base alloy [40, 48]. In majority of the zirconium based components, the gross texture is determined by the hot extrusion step which involves large strains [37, 42]. Subsequent steps of pilgering and annealing can lead to further developments such as strengthening specific texture component/fiber at the expense of other [36]. In dual phase alloys such as Zr-2.5%Nb, on the other hand the textural modifications subsequent to hot extrusion depend on the nature and morphology of the 2nd phase (beta phase) [47, 48]. Typically, the fuel tubes (Zircaloy-4) used in PHWR conditions are targeted to have their texture such that majority of the basal poles are aligned along the radial direction of the tube in view of the hydride related issues. The required texture in these tubes is achieved by adjusting the pilgering process parameters (thickness to diameter reduction ratio) in the cold working stage of the component manufacture. Pressure tubes of the PHWRs are manufactured with processing conditions which give rise to higher basal pole concentration along the transverse direction of the tubes in order to achieve better in-reactor creep performance [42]. Zr alloys undergo phase transformation from high temperature beta phase to low temperature alpha phase and the characteristics of this transformation can also govern the resulting texture [49]. In general, due to high number of variants coming from single beta grain [50], rapid quenching from the beta phase field leads to texture randomization or at least considerable texture weakening. Depending on the conditions of the phase transformation, some extent of variant selection leading to lower extent of randomization was observed in zirconium alloys [51]. Creep of Zr alloys: Understanding of the creep behaviour of Zr-2.5Nb alloy is of utmost importance for the comprehensive study of the deformation behaviour of pressure tube used in PHWR. The thermal creep behaviour of different generations of Zr-2.5Nb pressure tubes used in Indian PHWR in the temperature range of 350 °C to 450 °C and stress range of 0.7 to 0.9 times of the yield strength of the material has been studied. The accelerated creep tests were also carried out for the samples fabricated with its axis along the longitudinal and transverse direction of the pressure tube in the temperature range of 350 °C to 450 °C and stress range of 0.7YS to 0.9YS [52, 53]. Further, effect of hydrogen on the thermal creep behaviour was also studied by carrying out the creep tests of the hydrogen charged samples with different hydrogen concentrations in the temperature range of 350 °C to 450 °C and stress range of 0.7YS to 0.9YS. The effect of hydrogen in solid solution form and in hydride precipitate form was highlighted in the study [54]. All the creep tests were carried out at higher temperature and stress as compared to the actual working conditions of the pressure tube in PHWR (Temperature - 300 °C and Internal pressure—10 MPa). Therefore, to estimate the role of thermal creep at the reactor working conditions, a mathematical model known as Wilshire prediction model was used to predict the long-term creep properties using the accelerated creep tests data obtained in the previous studies [55].

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Hot working behaviour: Hot working is used for breaking the cast microstructure and achieving a uniform microstructure of preferably equi-axed grains. Experimental simulation of hot working was carried out by performing high temperature deformation tests in thermo-mechanical simulators through either uni-axial or plane strain compression experiments. From this, using the flow behaviour, strain rate sensitivity and microstructural characterization, the optimum window of hot working, in terms of temperature, strain rate and strain was determined. In general the corresponding kinetics equations relating stress to strain rate and temperature were also determined. Of particular interest is the dynamic recrystallization domain [56], where the flow stresses are lower and grains are equi-axed and of lower defect density. Lot of studies have been carried out on the hot deformation studies of Zr alloys (Zr-2.5Nb [57–63], Zircaloy [64, 65], Zr-2.5Nb-0.5Cu [66, 67] and Zr-1Nb [68]). The knowledge gained from the above studies helped in developing the flow sheets for fabrication of different zirconium based alloy components in NFC. The finished zirconium based component has to withstand the service conditions inside the reactor. So the degradation of zirconium alloys in the reactor environment has also been studied very well by carrying out a broad spectrum of experiments, the results of which are used in the zirconium based alloy development. Here the effect of irradiation and the effect of the different corrosive environment have been examined in detail including the deleterious effects of hydrogen. Hydrogen leads to formation of hydrides a phenomenon which has very severe influence on the life of the component resulting in premature failure. Therefore all aspects of hydride formation, viz. the influence of texture, microstructure and stress have been examined in detail and changes in the microstructure and texture have been carried out to make the effect of hydrides less significant. Development of better Zr alloys has been a continuous process. Efforts are on to improve the performance of Zr alloys by making modifications in the fabrication process like replacing the melting process from double arc melting to quadruple melting to reduce the interstitial content of the Zr alloys. NFC has replaced the old process for making pressure tubes by breaking the cast structure of the alloy by rotary forging, instead of using extrusion as the initial step for the same purpose [59]. This has resulted in better microstructure in the finished pressure tubes. NFC has also developed seamless calendria tubes of Zircaloy 4. Earlier these tubes were fabricated by welding. Studies have also been carried out in zirconium based rapidly solidified and bulk glasses which have very attractive mechanical properties. However, their thermal and irradiation stability in the reactor environment is yet to be ascertained. Another development in the area of zirconium based alloys for structural applications in reactors has been the study on Zr3 Al with up to 10% Nb [69]. These alloys have a cubic structure unlike the anisotropic hexagonal structure of Zr based alloys. The cubic structure posses a much less number of issues connected to texture. From neutron economy point of view, these alloys are good because these contain, zirconium and aluminium as main ingredients and both these elements have low neutron absorption cross section. These alloys are also much less susceptible to hydrogen related problems. However, the behaviour of these alloys under irradiation and temperature of the reactor environment is yet to be proven.

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Steels:Steels, stainless varieties and other types have been in use in the nuclear industry in good tonnage. However, these are well established varieties with their proven performance in this industry over years of operation. Introduction of a new variety needs very exhaustive testing with long term examination including in the harsh nuclear environments and hence replacement with new varieties are done only if there are frequent failures due to materials related issues. Occurrence of such instances has been very few. One example here which can be given is the replacement of the ferritic (3.5Ni) steel with austenitic steel due to the cracking of the component as a result of increased DBTT of the former [70]. Reactor Pressure Vessel is one of the critical and the only un-replaceable component of pressurized water reactor (PWR) that directly governs plant’s safe operation. Studies have been carried out mainly to understand the manifestation of broad range of phenomena influencing structural integrity of the vessel. These are related to transformation behaviour [71–73], hardenability [71, 72, 74], flow and fracture behaviour [75–78], the ductile to brittle transition [79–81] and its relation to irradiation [82, 83], and thermal aging [84], as well as dynamic strain aging phenomenon [72, 85–89]. In the category of steels, maraging steels of different grades deserve mention for their application as structural materials in many departments. These have been successfully developed by MIDHANI for use not only by DAE but also by DRDO and ISRO. Physical metallurgy of maraging steels has been thoroughly studied by the scientists of the country [90, 91]. Attempts have been made in BARC as well as IGCAR to develop iron based alloys including some of the stainless category with some future applications in view. A flavour of some of these is given in the following section. Ferritic/martensitic steels: Since late 1970s, ferritic/martensitic steels have been considered as candidate structural materials for fast and fusion reactors because of their higher swelling resistance, higher thermal conductivity and lower thermal expansion than those of austenitic steels [92]. However, keeping in mind the damaging capacity of the high energy fusion neutrons (14 meV), the reduced activation ferritic/martensitic (RAFM) steels are currently considered to be the most promising structural materials since they pose a reduced hazard from the induced radioactivity thanks to transmutation reactions [93, 94]. India has developed its own RAFM steel IN RAFMS (composition: 9Cr–1.4 W– 0.06Ta–0.1C) as a structural material for its Test Blanket Module (TBM) for ITER [94]. IN RAFMS has been produced by slightly varying the composition of the conventional modified 9Cr-1Mo steel (P91) where elements like molybdenum and niobium which produce long half-life transmutation products have been substituted by their comparatively lower activation counterparts, such as tungsten and tantalum [95]. The microstructure of IN RAFMS has been established through standard heat treatment of normalising and tempering and the steel was found to have a tempered martensitic microstructure with coarse M23 C6 carbides, rich in chromium and tungsten on the lath boundary and fine intra-lath tantalum and vanadium-rich carbides/nitrides [96]. The physical, thermodynamic and mechanical properties of IN RAFMS have been studied in detail while different fabrication processes like

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machining, Hot Isostatic Pressing (HIP) and welding have also been investigated [97]. The corrosion behaviour of IN RAFMS in the proposed coolant, lead–lithium eutectic (Pb–Li) has also been established over a wide range of operating parameters like temperature, flow velocity and magnetic field and a rational liquid metal corrosion mechanism has been proposed [98, 99]. Alloy D9: Type 316 austenitic stainless steel (SS) has been chosen worldwide as a standard cladding and wrapper material for prototype and commercial Fast Breeder Reactors (FBR) However, it is realised that at the large burn-ups required for economic operation of FBRs, the extent of void swelling in type 316 SS would be high. This has led to the development of titanium modified type 316 SS, known as Alloy D9 which can lead to an increase in the incubation dose from around 45 dpa for cold worked 316 SS to well beyond 100 dpa for alloy D9 [100]. Austenitic stainless steel alloy D9 (15Cr-15Ni-Mo-Ti-C) with specifically tailored composition, especially with regard to carbon and titanium content, has been chosen as the reference material for the wrapper and clad tubes of the Indian PFBR [101]. In the cold worked alloy D9, TiC forms preferentially on the intra-granular dislocations while M23 C6 precipitates on grain boundaries [102, 103]. TiC is more stable than M23 C6 and retains its finer size over longer durations contributing to higher rupture strength, lower creep rate and lesser void swelling [104]. A series of melting, casting and processing trials were carried out at IGCAR with a view to standardise the process parameters and mechanical properties of this material [100, 105]. The optimum level of cold work that would not lead to softening of the material due to re-crystallization was estimated to be 20% from Larson-Miller parametric approach [105, 106]. It was established that Alloy D9 with Ti/C ratio of 6 exhibited the best tensile properties while a ratio of Ti/C = 4 showed the best creep properties [106]. Considerable amount of work has been done under the National Mission established by a consortium comprising IGCAR, BHEL and National Thermal Power Corporation (NTPC) to carry out R&D and subsequent indigenization of materials to be used in Advanced Ultra supercritical (AUSC) technology where the steam pressures and temperatures will be touching 310 bar and 993 K respectively. Besides the consortium members, a host of other institutes across the country are contributing to this programme. The important iron based alloys being developed for this application are 304 H Cu and 10 Cr steel. Extensive work on evaluation of all mechanical properties and a detailed study of the microstructure has been done for bringing out the structure property correlation in these alloys. These were found to be comparable to the internationally available alloys. In addition to alloy development, techniques for making dissimilar alloy joints between some of the aforementioned alloys have also been developed. Some of these materials and concepts may also be used in nuclear power plants [107]. Improved stainless steels and oxide dispersion strengthened steels are being developed for higher fuel burn-up in the fast breeder reactors. For further improving the high temperature mechanical properties of 316 LN SS which is the main structural material for fast breeder reactors, addition of various amounts of nitrogen content were investigated. These newly developed steels have been found to have better

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combination of mechanical properties. Similarly micro-alloying of P91 steel with boron coupled with control of nitrogen is considered a possible way of reducing the strength disparities across the weld joint that will lead to reduction of cracking in the weld joints of this material [108].

5.4 Nickel-based Alloys Nickel based alloys are mostly used in heavy water plants and waste immobilisation facilities in DAE [109–113]. Alloy 625 [109–111, 113] is the common choice for the former application and alloy 690 is the choice for the latter. Some of the alloys in this category are precipitation hardenable whereas others are solid solution strengthened. Besides this, both alloy 600 and alloy 800 have been used for heat exchanger applications; earlier use of alloy 600 having been replaced later by alloy 800 [114] in nuclear power plants. Most of these alloys are melted and subjected to further processing in MIDHANI. However, for making tubular products these are sent to NFC. In addition to heavy water plants, Alloy 625 is also going to be used in the AUSC programme [108]. Another Ni based alloy which is going to play a very important role in the AUSC programme is the Alloy 617 [108]. Both these alloys have been indigenously developed and their properties have been found to be of international standard. The Alloy 690 has been identified as the material for construction of inductionheated metallic melter pot and as electrode material of Joule- heated ceramic melter pot; this has been based on extensive laboratory scale tests on compatibility between alloy material and the borosilicate melt used for waste immobilisation. However, under harsh service conditions related to vitrification of high level nuclear wastes, the materials degraded prematurely leading to failure of the furnaces. Simulated experiments showed significant depletion of Cr from the alloy/borosilicate melt interfaces followed by formation of discontinuous refractory layers (consisting of Cr2 O3 , Ni2 CrO4 and NiCrO4 ) which disturbed the ionic conduction and heat distributions within the melt. Formation of cracks and intergranular carbide precipitates were also noted within the alloy [115–118]. To circumvent this problem, Alloy 693 (with additional 2.5 wt% Al on Alloy 690 composition) was tried and it was found to give better corrosion resistance due to formation of Al2 O3 layer (having better continuity on alloy surface) at the alloy / borosilicate melt interface [119]. Mention can also be made here of the fact that, the technology for the fabrication of NiTi shape memory alloys has been developed by BARC and has been handed over to ADA (Aeronautical Development Agency) [120–122].

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5.5 Niobium-based Alloys The occurrence of niobium bearing ores in different parts of the country and the noibium content in these is known. Besides these, carbide sludge from the carbide tool-scrap also contains recoverable amounts of tantalum and niobium [123]. The process for production of niobium from Indian resources has been developed by BARC and is being implemented in NFC. Dissolution in hydrofluoric acid and hydroprocessing for separation of niobium and tantalum is done for the production of pure oxides of niobium and tantalum. Niobium pentoxide is subjected to open aluminothermic reduction to produce the thermit metal containing about 3% aluminium and oxygen & nitrogen at few hundred ppm level which is melted and purified by using high temperature electron beam furnace [124]. At NFC, the process was further modified by introducing granule-feeding arrangement and in-situ electron beam melting. The ingots so produced are either used for alloy making or are melted several times for further purification. Such highly pure niobium ingots are used for various superconducting applications [125]. In addition to the extraction of Nb metal from ore, alloys of niobium in 30–50 kg batches which are being considered for structural components in the High-Temperature-Reactors (HTR), was developed at NFC. The most popular nuclear application of niobium metal is for production of PHWR pressure tubes made out of Zr-2.5Nb alloy. In addition, alloy like Nb–1Zr– 0.1C is also considered for structural components in the High-Temperature-Reactors (HTR) [126]. Unlike niobium, its twin metal—tantalum does not find any direct application in nuclear industry but in demand in electronic industry as tantalum capacitor. Low temperature processing flow sheet for preparing the niobium alloy into various shapes was also developed. It was prepared by carrying out structure–property correlation studies of as-cast, deformed and recrystallised samples at different temperatures and time. A deformation map was developed by studying as-cast and deformed materials at different temperatures and strain rates and optimum extrusion temperature for processing and recrystallisation was determined [127, 128]. An issue of formation of various carbides in the Nb–1Zr–0.1C alloy was addressed [129, 130]. Oxidation behaviour of Nb alloy was studied in detail and methodology of Si-coating on the alloy was developed at BARC [131, 132].

5.6 Vanadium-based Alloys The occurrence of vanadium ore in the country is documented [133–135]. Aluminothermic reduction of V2 O5 and purification of vanadium by electron beam melting and molten salt electro refining have been done in a limited scale in BARC [136]. Vanadium has high solubility for nitrogen which is detrimental for the low temperature properties. However, the removal of nitrogen from vanadium is thermodynamically not possible as the vapour pressure of vanadium and nitrogen are nearly same at its

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melting point. It, is therefore, technologically challenging to remove nitrogen from V. In BARC, this was achieved by using closed bomb alumino-thermic reduction [136] and molten salt electro refining techniques. Alloys of vanadium (Vanadium-aluminium and Vanadium–iron master alloys) are in demand by aero space and steel industry to produce Ti-6Al-4 V alloy and high strength low alloy steels respectively. Detailed study has also been attempted at BARC on alloy development of vanadium [137–139] for its application as the first wall structural material for fusion reactors.

5.7 Archiving of Knowledge-Bank Much of the knowledge in this field is archived in journals and reports, many of which have been referred in this article. In addition, the vast information collected by the scientists is archived in the case of many of the metals in the form of books where the extraction process developed in the country starting from ore has been the subject [33, 140–144]. These volumes can be consulted in case a detailed account of extraction of many of the metals mentioned in the aforementioned sections is required. Future directions: There is a need to update and use the cutting edge technologies in each of the domains involved starting from mineral exploration, ore dressing, and extractive metallurgy to alloy processing. Extensive use of modelling to substitute empirical approaches/trial and error approach with ab-initio approaches in as many areas as possible needs to be done. This will lead to better quality of the products with considerable saving of time and energy. Initiation has been done and some distance has been travelled in this direction in each of the domains involved. However, the level of advancement is not the same in all the domains. The extent of use of modelling is less in some of the domains. The science of Computational materials has made significant progress and is likely to make alloy design for a particular application much easier. Advancement in modelling alone is not sufficient. There is a need to continue with blue sky research as much as possible so that the knowledge base continues to grow. There is also a need for transferring the lab-scale technologies for extraction from Indian resources to bench scale and then at least to pilot plant scale to ascertain the problems which will be encountered after scaling up.

6 Conclusions India can be considered self-reliant in materials in use for nuclear energy generation and capable of developing new materials as and when needed because of the large trained scientific force and the existing knowledge-bank. There is a continuous

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need of updating this knowledge base by doing blue sky research and adopting the latest modelling and simulation techniques. This will reduce the use of the empirical approach and facilitate adoption of well formulated pathways based on a deeper understanding of each process. There is a need for modernisation of the production facilities for improving efficiency and also for reducing cost; this can be achieved through induction of modern concepts like Artificial Intelligence in process control. Acknowledgements It is a pleasure to acknowledge the benefit of many discussions which the author had with colleagues. In this context, the author will like to express his gratitude to Dr. A. K. Bhaduri, Dr. Magangopal Krishnan, Dr. V. Kain, Dr. T. Sreenivas, Dr. R. Tewari, Dr. Alok Awasthi, Dr. R. N. Singh, Dr. S. Majumdar, Dr. D. K. Singh, Dr. Tarashankar Mahata, Dr. Kinshuk Dasgupta, Dr. K. V. Manikrishna, Dr. Poulumi Chakraborty and Dr. Uttam Jain.

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Advanced High-Temperature Structural Materials in Petrochemical, Metallurgical, Power, and Aerospace Sectors—An Overview Pradyut Sengupta and Indranil Manna

1 Introduction In the first two decades of the twenty-first century, humankind witnessed an unprecedented rate of progress in almost all major engineering sectors [1]. These include aerospace, automobile, transportation, computer and automation, biotechnology, civil construction, electrical devices, electronics and instrumentation, metals and materials, mechanical and manufacturing, marine and naval, and even exploration of polar and extra-terrestrial space. The design and development of a new breed of structural materials have not only ushered in many paradigm-shifting technologies, but also have paved the way for accelerated growth of economy and prosperity. Despite remarkable progress, the necessity of developing novel structural materials, mostly metallic, to meet the demand of futuristic technologies has not faded away. Materials are the backbone of all hardware as the performance and reliability of all components, devices, machines, and systems, from highly intricate and miniature to most complex and gigantic, ultimately depend on the physical material that they are built of. Innovations in the form of nanostructured films and solids, carbon-based one- or twodimensional materials and novel compound semiconductors, synthetic molecules and supra-molecules, and glasses have made structural and functional components more efficient, reliable, economical, and robust than ever before. But the quest continues,

P. Sengupta · I. Manna (B) Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur, W.B 721302, India e-mail: [email protected] P. Sengupta CSIR – Institute of Minerals and Materials Technology, Bhubaneswar 751013, India I. Manna Birla Institute of Technology (BIT), Mesra, Ranchi 835215, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_5

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for newer, better, lighter, and stronger, particularly for structural, more so for hightemperature structural materials. Indeed, the most intensely pursued domain of material development for structural applications primarily concerns metallic and nonmetallic alloys that are not only lighter and stronger, but also can withstand higher levels of threats of thermal, mechanical, and chemical nature at high temperature. Many a time, paucity of suitable structural material acts as the principal hurdle against realizing many critical aspirations of humankind. With the advent of newer structure or architecture of materials, modern and novel processing techniques, and the emergence of more effective material characterization facilities aided by advanced computational and simulation tools, the prospect of development of novel structural materials with hitherto unrealized properties and functionalities is now more imminent than ever before. For sustainable growth and self-reliance of any country, the manufacturing sector has a crucial role to play [2–4]. With the motivation to review the latest developments and highlight the major challenges that need immediate attention of the engineering community, the present article attempts to discuss the current status of structural materials pertaining to different engineering applications in petrochemical, metallurgical, thermal power, nuclear power, aviation, and space sectors. The objective of this review is to focus on the future landscape of high-temperature structural materials primarily pertaining to these specific engineering sectors.

2 Structural or Mechanical Properties at Ambient and Elevated Temperature The critical assessment in terms of structure–property correlation has always paved the way for developing new materials for specific applications. In the course of new material development, the response of a material to an external stimulus is investigated extensively to get an insight into its salient characteristics. A mighty blow of a hammer shatters a glass pane on the window but only creates a dent on a sheet of metal. The conclusion is that glass is brittle but metal is tough, though both may exhibit a good combination of elastic modulus and yield strength. Table 1 summarizes the salient features of different classes of engineering materials [5, 6]. It is needless to mention that properties form the basis for the selection of materials for engineering applications and define the level of performance of the engineering component or device made out of that material. Interestingly, properties do change either by the change in composition or simply by tailoring the microstructure. Furthermore, properties may drastically vary or degrade due to the influence of the environment or working conditions in terms of temperature, pressure, atmosphere, etc. Temperature can have the most dramatic effect as it can change the structure, stability, physical state, and obviously the overall behaviour. In general, engineering properties are of two types, namely structural (response to mechanical activation) and functional (response to thermal, electrical, magnetic, chemical, and

Ceramics

Non-ferrous alloys (including superalloys)

Ti alloys

304

3.3

Hot pressed Si3 N4

380 207–483

3.98

Hot pressed SiC 3.3

Al2 O3

99.3

6.51

Zr (reactor grade)

204.9 236

8.19

Inconel 718

207

114

110

103

204

200

193

193

Haynes alloy 25 9.13

8.44

4.43

Ti-6Al-4 V

Inconel 625

4.48

7.65

17-7PH

Ti-5Al-2.5Sn

7.80

AISI 440A

4.51

8.00

AISI 316

ASTM grade 1 (commercial)

8.00

7.85

AISI 304

207

7.85

AISI 4340

Stainless steel

207

7.85 207

207

7.85

Plain carbon AISI 1020 and low alloy AISI 1040 steel AISI 4140

Modulus of elasticity (GPa)

Density (g/cm3 )

Materials

Table 1 Characteristics of various engineering materials [5, 6]

590b 1720c 1760c

375b 1570c 1620c

16 10g 42.5

790f 1172g 930f

760 1103g

–

–

–

207

445

1100

517

62 16h – – –

379h 282–551i 230–825i 700–1000i

25 970

1375

30

240f

170

3.5e

1450e

1310e

5d

1790d

30

620

310

10

12c

11.5c

28b

38.5a

% elongation

1650d

860

440a

345a

515

Tensile strength (MPa)

Yield strength (MPa)

2.7

4.6

7.4

59

12.3

13.0

12.8

8.6

9.4

8.6

11.0

10.2

15.9

17.2

12.3

12.3

11.3

11.7

Coefficient of thermal expansion (× 10–6 /°C)

29

80

3.9

22

9.8

(continued)

11.4

9.8

6.7

7.6

16

16.4

24.2

16.2

16.2

51.9

51.9

51.9

51.9

Thermal conductivity (W/mK)

Advanced High-Temperature Structural Materials … 81

ZrO2 (3–12 mol.% Y2 O3 )

5.85–6.10

Density (g/cm3 )

200–210

Modulus of elasticity (GPa)

–

Yield strength (MPa)

% elongation

–

Tensile strength (MPa)

800–1500i 10.3–11.0

Coefficient of thermal expansion (× 10–6 /°C) 2.2–2.5

Thermal conductivity (W/mK)

(a normalized at 925 ◦ C, b normalized at 900 ◦ C, c oil quenched and tempered at 315 ◦ C, d tempered at 315 ◦ C, e precipitation hardened at 510 ◦ C, f annealed, g solution heat treated and aged, h cold worked and annealed, i flexural strength)

Materials

Table 1 (continued)

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similar non-deforming activation). This chapter is devoted to behaviour of structural materials at elevated temperatures. Thus, it is pertinent to first narrate the mechanical properties of interest at ambient and then those relevant at high temperatures. Strength is the primary criterion for the design, development, and selection of materials for structural or load-bearing applications either in static or dynamic conditions. However, it is not a unique property; its definition and requirement can widely vary depending on the nature (static, dynamic, cyclic, or alternating), direction or type (tension, compression, torsion, oe shear), and condition (temperature and strain rate) of loading. Typical strength parameters or properties of the importance of an engineering solid at ambient temperature are hardness, elastic/shear/bulk modulus, yield stress, strength under tensile/compressive/torsional/shear deformation, impact toughness, and fatigue strength. Degradation or failure may occur due to interaction with the environment in the form of wear, friction, erosion, corrosion, etc. Technically, the strength of metals can be described in terms of relative difficulty or ease of sliding or gliding of dislocation on the slip plane by the resolved shear stress component of the overall applied load. This resistance to dislocation movement can arise from multiple sources and circumstances. The most effective strategies for resisting easy gliding of dislocation or plastic deformation can be through [5, 7, 8]: – solid solutions strengthening (due to stress field around a bigger or smaller solute atom), – grain refinement and structure (due to barrier to dislocation movement from larger specific grain boundary area and/or type and structure of the boundaries), – phase transformation (due to change in the crystal structure), – precipitation hardening or coherency strengthening (due to formation of uniformly distributed precipitates that are coherent with the matrix), – dispersion hardening (due to physical barrier posed by foreign, insoluble, and incoherent particles), – strain hardening (due to cold deformation and increase in dislocation density), and – supplementary methods like crystallographic texture, composite aggregate, etc. An alloy for structural application tends to utilize one or more of these strategies depending on the alloy composition, solubility, service condition, prior history, dimension of the components, etc. While the above description holds good in general for application of metals at room temperature, the criterion for selection, design, and application of materials at elevated temperature is fairly different as the deformation and failure mechanisms could be marginally to entirely different depending on the nature and identity of the component, service condition, and environment for an application at elevated temperature, particularly, above the equi-cohesive temperature (i.e., the temperature where the strength of the grain body equals that of the grain boundaries). In addition to the strength properties mentioned earlier for room temperature application, special attention must be given with regard to creep, thermal fatigue, oxidation damage, etc. Constitutionally, ceramic materials are different than metals in terms of bonding characteristics and the manifestation of properties under load or mechanical stresses.

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Thus, mechanical properties, even if they sound similar, the range and response would be fairly different. As a result, the degradation and failure mechanisms are also entirely different. For instance, the dislocation-aided deformation mechanism is nonexistent in ceramic oxides or compounds. Thus, not only do hardness and strength values differ, deformation and failure methods and limits are also very different than those of metals. Understanding these differences is of paramount importance while designing a system with multiple components with diverse nature of materials aimed at different functions and applications. In this connection, it is worth mentioning that the term ‘elevated temperature’ used in this chapter mainly refers to the temperature regime above the recrystallization or equi-cohesive temperature of the concerned material, though temperature above the boiling point of water is also considered elevated temperature as in petroleum or power generation sectors. It may be pointed out that the severity of the threat to hardware arises not just from temperature alone but thermal combined with pressure and environment can also severely aggravate the damage potential. As this chapter focuses on discussing high-temperature structural materials in different engineering sectors and the actual application temperature varies from one sector to another, a sectorspecific discussion is presented on currently used materials and limitations thereof to avoid over-simplification and related confusion. Accordingly, Sect. 3 provides an overview of service conditions and challenges faced in five specific engineering sectors, namely petrochemical, metallurgical, power generation, aviation, and space.

3 Sector-Specific Service Conditions and Challenges 3.1 Petrochemical (Oil and Gas) Petrol and diesel, derived from crude petroleum, are the main hydrocarbon-based fuel for running the automobiles. Petroleum products are also essential to heat buildings, run machines and motors, and produce electricity. In the industry, petroleum is a raw material to produce various polymeric products or plastics, polyurethane, solvents, and several varieties of semi or finished consumer goods (lipsticks, gels, etc.). The yield of petrol or gasoline by fractional distillation is about 50% from the raw petroleum (say, 19 gallons from about 42 gallons of crude). Like gasoline, natural gas is a non-renewable mixed hydrocarbon compound that is an equally common source of energy for heating, cooking, and electricity generation. It is now widely used as a fuel for running vehicles and as a chemical feedstock for synthesizing plastics and organic chemicals. Several useful products like gasoline, diesel, naphtha, asphalt, heating oil, kerosene, liquefied petroleum gas (LPG), and aviation jet fuel are produced in petroleum refinery through an industrial process of fractional distillation. The typical process flow diagram of an oil refinery is shown in Fig. 1 [9]. A typical petroleum refinery plant consists of several machines, heaters, pipes, tanks,

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Fig. 1 The typical process flow diagram of an oil refinery (adapted from [9] available in the public domain)

distillers, condensers, turbines, fans and blowers, valves and fittings, rollers, bearings, elevators, and conveyors—most of which are exposed to elevated temperature and/or pressure, as well as to the highly corrosive and aggressive environment. Table 2 shows the service condition, structural material, and associated challenges in petroleum refinery [10]. The major problem encountered in the oil and gas industry is corrosion and hot corrosion of different structural components, which accounts

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Table 2 The service condition, structural materials, and challenges in petroleum refinery [10] Application/ system/ component

Service condition of different components

Structural materials

Challenges

Petroleum refinery

Crude distillation:

High-temperature sulphidation, Corrosion due to naphthenic acid

AISI 405, 410, 304, 316

Fluid catalytic cracker:

T ~ 493–527 ◦ C, Tregenerator > 760 ◦C

AISI 304, 321, 347

Delayed coker:

T ~ 510 ◦ C

AISI 304, 316, 410

Hydrotreater:

T ~ 370 ◦ C

AISI 304, 308, 321, 347, 405, 410, 430

• Corrosion (galvanic, pitting, CO2 , O2 , H2 S, crevice, erosion, microbiologically induced) • Hydrogen embrittlement, • Sulphide stress corrosion cracking

Catalytic reformer:

Corrosion due to organic chloride

AISI 304, 329

Hydrocracker:

T ~ 343–455 ◦ C, P 304, 321, 347, ~ 8–20 MPa 410, 430

Hydrogen plant: Teffluent ~ 816 ◦ C, P ~ 2.8 MPa

AISI 304, 304L, 310, 330, 410, 430

Gas processing plant:

Corrosion by ammonium chloride, ammonium sulphide, and cyanide

AISI 304, 304L, 316, 329, 330, 405, 410

Alkylation:

Corrosion due to sulphuric acid

AISI 316, 316L, Ni-based alloy

for huge economic loss (a few billion USD/year) [11, 12]. The rate of corrosion in pipelines is dependent on several factors like the surface of the steel, flow velocity, temperature, the content of CO2 and H2 S, etc. The different forms of corrosion observed in the oil and gas industry include general or uniform corrosion, galvanic corrosion, erosion corrosion, stress corrosion cracking, oxygen corrosion, crevice corrosion, sour corrosion (due to H2 S), sweet corrosion (due to CO2 ), etc. [13, 14]. The presence of CO2 and H2 S leads to the formation of FeCO3 and FeS as corrosion products, respectively. The corrosion in the oil and gas industry can be mitigated by proper choice of material, use of a protective coating of appropriate thickness, cathodic protection, periodic maintenance and inspection, etc. [15].

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3.2 Metallurgical Sector For structural applications, metals continue to be the most widely used engineering material primarily due to the combination of mechanical strength, ductility, toughness, fabricability, castability, durability, recyclability, and cost benefits. Furthermore, the properties of a given metallic alloy can be significantly varied over a wide range by appropriate design of composition, microstructure, and process parameters. Usually, metallic products are either cast or wrought type. Castings are made from molten metals directly poured into a mould and solidified as the final product. On the other hand, wrought products must undergo successive stages of deformation, thermal and thermomechanical treatment, and machining before an ingot reaches the semi or finished product stage. Irrespective of the end application, the equipment that are essential for making, shaping, and treating metals to make the final product include furnaces, foundry devices, forging press, rolling mills, welding and joining units, etc. Among all such equipment, furnaces, not just of one single but of multiple shapes, sizes, capacities, designs, and purposes do play a very important role as they cater to operations from extraction, homogenization, heat treating, fabrication, and finishing. Furnaces are primarily isolated and confined zone capable of maintaining specific thermal and atmospheric conditions for various manufacturing operations. Besides heating elements, temperature and atmosphere control, and loading/unloading devices, the precision, utility, and life of a furnace largely depend on the thermal insulation and load-bearing capability for an extended period of continuous or intermittent use provided by the insulating boundary; this can be made of refractory bricks, castable or ramming mass of thermally insulating materials, or ceramic fibres. Despite its importance and exclusivity, high-temperature refractory materials in any form do not receive due attention for research and development. One such very important area is the inner lining of different furnace chambers or vessels used in integrated steel plants and metal manufacturing units. Over the years, the scope of developing new refractory in primary and secondary steelmaking processes has reached almost a stage of saturation. Thus, the current focus is on enhancing the operating life of various refractory-lined vessels to ensure that the unexpected breakdown, often leading to loss of human life, interruption in production schedule, and damage of costly equipment, can be avoided or prevented. Table 3 highlights the service condition and corresponding refractory materials and challenges [16]. As steel making in basic oxygen furnace (BOF, Fig. 2) is primarily an oxidation-decarburization process, in addition to the quality of refractory, the campaign life of BOF basically depends on several factors like quality of operation, slag splashing, tap to tap time, maintaining proper basicity of slag, periodic maintenance of tap-hole area, etc. Despite tremendous improvement in quality of refractory as well as the advancement of technology in steel melting and continuous casting shops, the puncture of BOF, steel ladle, failure of slide gate, failure of flow control refractories (ladle shroud, sub-entry nozzle, etc.), tundish, and subsequent damage of production schedule as well as costly equipment are not entirely

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Table 3 Operating condition, structural materials, and challenges in the iron and steel sector Application/ system/ component

Temperature range

Service condition

Structural materials

Challenges

Basic oxygen The inner lining furnace must withstand the temperature of hot metal

• High-temperature • Impact of hot metal, Slag corrosion, Localized erosion, blowing of oxygen

•Refractory lining: Working lining: Metal zone: resin-bonded MgO-C Slag zone: resin-bonded MgO-C Charge pad: Spinel Back-up lining: Fire clay or MgO refractory

• Increase the lining life • Accidental failure due to local corrosion • Local failure of tap-hole region, Prediction of wear, lifetime

Steel ladle

The inner lining must withstand the temperature of molten steel

• High-temperature • Impact of hot metal, Ar purging, Arcing, Slag corrosion

•Refractory lining: Working lining: Metal zone: resin-bonded MgO-C Slag zone: resin-bonded MgO-C Charge pad: Spinel Back-up lining: Fire clay or MgO refractory

• Accidental failure due to improper operating condition • Excessive corrosion at slag-metal interface • Slide gate failure, Puncture of ladle

RH degasser

The inner lining must withstand the temperature of molten steel

• High-temperature • Localized erosion • Slag corrosion

•Refractory • Erosion in alloy lining: chute, lower Gas duct, alloy vessel • Corrosion, chute, and upper erosion, and vessel: Direct thermal shock bonded magnesia in snorkel chrome Lower vessel, leg, and snorkel: Pre-reacted magnesia chromite sinter

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Fig. 2 Overview of steelmaking through basic oxygen furnace (BOF) route (reproduced with permission from [16])

uncommon. Therefore, the real-time scanning of residual refractory lining thickness may help in estimating the remaining life of the vessel so that unforeseen breakdowns can be avoided. Since the refractory consumption is directly related to the volume of crude steel production, the demand for refractory is expected to be higher in the next few decades as India has set an ambitious target of producing 300 million tons per annum (Mtpa) crude steel by 2030–2031 [17]. However, most of the crucial ingredients of refractory materials are imported (from China), and therefore, the import substitution is likely to play a decisive role for self-sustenance in refractory.

3.3 Power Sector 3.3.1

Thermal Power

Next to the sun, water, and atmosphere, energy is the primary source of sustenance of life on earth. In particular, energy security and sustainability are of the utmost priority of all nations in the present time, be it developed, developing, or under-developed. With over 1.4 billion people (nearly 1/5th of the world population), it is no wonder that India is the world’s third largest producer as well as consumer of electricity. As of 31 October 2020, the installed capacity of the national electric grid in India is 373.436 GW. Renewable power that includes hydro, wind, and solar accounts

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Fig. 3 The evolution of coal-fired thermal power technology. The future is advanced ultrasupercritical thermal power plant (adapted from [21] available in the public domain)

for 36.17% of India’s total installed capacity of electricity generation. Despite the country’s rapid progress in the field of alternative energy, thermal power plants still supply over 51% of the total generation and continue to be the most popular source of energy primarily due to the abundance of coal in the country. Figure 3 shows the classification and evolution of four generations of coal-fired thermal power plants from the initial version of subcritical power plants operating at 175 bar and 565 °C to the most recent advanced ultra-supercritical (AUSC) version operating at around 330 bar and 650–670 °C. The operating efficiency of a coal-fired thermal power plant depends on its operating temperature. The older generations of thermal power plants in India were of a ‘subcritical’ nature, where the operating temperature was around 500 °C. With the thrust to enhance the efficiency and reduce the emission of COx , SOx , NOx, and other hazardous gases, there has been a major shift in abandoning the ‘subcritical’ operation regime and adopting the ‘supercritical’ technology. At present, the efficiency of several supercritical thermal power plants in India lies in the range of ~33–40%. In order to achieve better thermal and operational efficiency, the operational temperature regime in all active parts of the thermal reactor is projected to be raised to 650–750 °C. Thus, nearly the entire set of metallic materials used for crucial parts of the steam generation to delivery including the boiler, pipes, superheaters, nozzles, discs, and turbines needs a change to withstand higher temperature and pressure for an extended period of time. Table 4 illustrates the temperature, service condition, structural material, and challenges encountered in coal-fired power plants. The structural materials used in the boiler tube of subcritical power plants are as follows: C–Mn Steel, ½Mo (T1), 1¼Cr½Mo¾Si (T11), 2¼Cr1Mo(T22), AISI 304, AISI 310, AISI 316, AISI 321, and AISI 347. The operating temperature in supercritical power

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Table 4 Chemical composition, proof strength, tensile strength, elongation, and Vickers hardness of different alloys used in advanced coal-fired power plants [22–25] Application/ Temperature system/ component range

Service condition

Structural materials

Challenges

25 MPa/565 ◦ C/565 ◦ C

• Ferritic and austenitic steel

Low operating efficiency, emission of greenhouse gases

Boiler (a) Supercritical

538–566 ◦ C

(b) Ultra-supercritical

Up to 760 ◦ C 27.5 MPa/600 ◦ C/620 ◦ C

• Creep-strength enhanced ferritic steel • Advanced austenitic stainless steel

To improve operating efficiency and further reduce the emission of greenhouse gases

(c) Advanced ultra-supercritical

> 700 ◦ C

• Ni-based alloys

To develop suitable structural materials for advanced ultra-supercritical technology to serve harsh operating conditions (34.5 MPa/760 ◦ C/780 ◦ C)

33 MPa/650 ◦ C/670 ◦ C

plants is 600–650 °C, which is 50 °C higher than the operational temperature of subcritical power plants. However, advanced countries like USA have progressed further to enhance the operating efficiency of coal-fired power plants [18, 19]. In India, the first ultra-supercritical thermal power plant was commissioned in 2019 [20]. The advanced ultra-supercritical (AUSC) boiler (700 °C) is an emerging technology for high-efficiency coal-fired thermal power plants [21]. It is envisaged that if the steam temperature increases from 600–650 °C to 700–760 °C, the operating efficiency will also increase. The use of advanced steam cycles, with steam temperature ~760 °C, can enhance the efficiency of the thermal power plant from 47%, and consequently, the overall emission of CO2 gets reduced by ~10–35% [18, 19]. The structural material in the boiler tube of the supercritical thermal power plant is austenitic 22Cr25NiWCoCu stainless steel [22], which offers several important properties like excellent creep strength, oxidation resistance, structural stability, and ease of fabrication. The chemical composition and relevant mechanical properties of different structural materials of coal-fired power plants are summarized in Table 5 [22–25]. In the reheater and superheater tubes, Ni-based alloys like IN 617, CCA 617, Haynes 230, and IN 740 are of prime importance for application in the 760–800 °C temperature range [18, 19, 24–26]. High Cr and low Mo-containing Ni-based alloys are also suitable for fireside corrosion. It is expected that the enhancement in efficiency will enable the coal-fired thermal power plants to produce electricity at a cheaper rate with a simultaneous reduction in the emission of greenhouse gases.

Chemical composition (wt.%)

Fe-22.5Cr-25Ni-3.6 W-1.5Co-3.0Cu-0.5Nb-0.23 N-≤ 0.1C-0.2Si-0.5Mn-≤ 0.015S

Ni-22Cr-14 W-2Mo-3Fe(max)-5Co(max)-0.5Mn-0.4Si-0.5Nb(max)-0.3Al-0.1Ti-0.1C-0.02La-0.015B(max)

Ni-20Cr-10Co-8.5Mo-2.1Ti-1.5Al-1.5Fe(max)-0.3Mn(max)-0.15Si(max)-0.06C-0.005B

Ni-(14–15.7)Cr-(0.9–1.5)Ti-(4.5–4.9)Al-(18–22)Co-(4.5–5.5)Mo-0.17C (max)-1.0Si(max)-0.2Cu(max)-1.0Fe(max)-1.0Mn(max)-0.0015Pb(max)-0.010S(max)-0.15Zr(max)-(0.003–0.010)B

Materials

22Cr25NiWCoCu stainless steel

Haynes 230

Haynes 282

Nimonic 105

8.10

8.27

8.97

8.1

Density (g/cm3 )

1290–1345

1300–1375

1301–1371

–

Melting range (◦ C)

Table 5 Temperature, service condition, structural materials, and challenges encountered in coal-fired power plants

776

699–715

1140

1132–1147

837–852

≥ 680

≥ 310p , ≥ 355q

383–417

Tensile strength (MPa)

Proof strength (MPa)

Mechanical properties

22

30

46–47.3

≥ 40p,q

Elongation (%)

865 680

650

(continued)

989 600

41

550

83 927

1000 h

262 871

Temp. (◦ C)

552 760

35

649

57 927

1000 h

125 871

Temp. (°C)

248

50

800

760

85

750

649

145

700

1000 h

230

650

Temp. (◦ C)

10,000 h

Temp. (◦ C)

Creep-rupture strength

92 P. Sengupta and I. Manna

Chemical composition (wt.%)

p,q stand for 0.2% offset yield strength and 1% offset yield strength, respectively

Materials

Table 5 (continued) Density (g/cm3 )

Melting range (◦ C) Proof strength (MPa)

Tensile strength (MPa)

Mechanical properties Elongation (%) 700

495

Creep-rupture strength

Advanced High-Temperature Structural Materials … 93

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P. Sengupta and I. Manna

Nuclear Power

For a developing country like India, nuclear power is extremely necessary in order to meet the rapidly increasing demand for energy, without causing any environmental hazard. At present, nuclear power generation in India accounts for a meagre 1.8% (6780 MW) of the overall demand for energy. As the cost-effective nuclear power is a sustainable solution for a growing economy like India, it is of paramount importance to design structural materials indigenously to ensure self-sustenance. Owing to excellent corrosion resistance, heat resistance, high thermal conductivity, and low thermal neutron cross section, Zircaloy found application as a cladding material in water reactors [27, 28]. Fukushima-Daiichi nuclear disaster [29], which is considered as the most devastating nuclear disaster since the infamous Chernobyl disaster [30], occurred due to a loss-of-coolant accident leading to nuclear meltdown and hydrogen explosion. It was estimated that an enormous amount (~18,000 TBq) of Cs137 was released to the Pacific Ocean immediately after the accident, causing a serious threat of radioactive contamination. Even though Fukushima-Daiichi nuclear disaster was ascribed to the failure of the cooling system, the material community demonstrated active interest to develop novel high-temperature structural materials for critical components of both fusion as well as fission reactors. As a consequence, after the disaster, many research groups have demonstrated laudable research work on the design and development of new structural materials to survive unforeseen natural disasters in future reactors, as an alternative to Zr alloys [28, 31, 32]. Table 6 summarizes the operating conditions, structural materials, and challenges faced in various types of nuclear reactors, and Fig. 4 presents a schematic of a graphite-moderated very high-temperature reactor (VHTR) [27]. Globally, the research on developing new structural materials for the nuclear power sector is being undertaken along three major verticals: ferritic-martensitic (FM) steel, oxide dispersion-strengthened (ODS) steel, and ceramic matrix composite (CMC) [33–39]. Section 4 highlights the latest development on FM steel, ODS steel, and CMC, in a concise manner.

3.4 Aircraft Engine In 1939, when the first jet plane was built, the service life of a turbine blade was only 10–25 h at 650 ◦ C [40]. Owing to the continued research effort by engineers and scientists, the operational lifetime of turbine blades in the modern jet engine now is 50000 h or more even if the surface temperature is ~1150 ◦ C. Figure 5 shows the various sections of an aero-jet turbine engine [41]. The typical weight of a commercial aircraft engine lies in the range 2000–8500 kg, where metallic materials account for ~85–95% of its total weight [42, 43]. For commercial aircrafts, the major challenge lies in increasing the thermal efficiency of the engine in order to achieve lower carbon emission and reduce the overall noise pollution level to meet the strict environmental norms. Therefore, the demand to enhance the turbine inlet temperature has been the key driving force for material development and engine design. Table 7 summa-

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rizes the temperature range, service condition, currently used structural materials, and operational challenges of aero-engine. Superalloys are the materials of choice for high-temperature gas turbines. For example, in Ni-based superalloys, the addition of Al leads to the formation of the precipitates of Ni3 Al. The size and volume fraction of the Ni3 Al (γ  ) phase are important for the high-temperature mechanical properties of Ni-based superalloys. Nowadays, ceramic matrix composites have Table 6 The temperature range, service condition, structural materials, and challenges in different nuclear reactors [27] Application/ system/ component

Temperature range

Service condition

Structural materials

Challenges

Pressurized water Tinlet : 290 ◦ C, reactor (PWR) Toutlet : (Generation II) 320–325 ◦ C

P: 15–16 MPa • Cladding • Maximum Neutron spectrum: material: service Thermal, Zircaloy temperature of Zr Maximum dose: ~ • In-core: alloy is 400 ◦ C stainless steel, • Hydrogen 80 dpa Ni-based embrittlement, alloys loss-of-coolant • Out-of-core: accident stainless steel, Ni-based alloys

Boiling water reactor (BWR) (Generation II)

Tinlet : 280 ◦ C, Toutlet : 288–330 ◦ C

P: 7 MPa • Cladding • Maximum Neutron spectrum: material: service Thermal, Zircaloy temperature of Zr Maximum dose: ~ • In-core: alloy is 400 ◦ C stainless steel, • Hydrogen 7 dpa Ni-based embrittlement, alloys loss-of-coolant • Out-of-core: accident stainless steel, Ni-based alloys

Pressurized heavy water reactor (PHWR) (Generation II)

Tinlet : 270 ◦ C, P: 10 MPa Toutlet : 310 ◦ C

• Cladding material: Zircaloy 4

• Hydrogen embrittlement, loss-of-coolant accident

Advanced gas-cooled reactor (AGR) (Generation II)

Tinlet : 340 ◦ C, P: 4 MPa Toutlet : 635 ◦ C

• Cladding material: Austenitic stainless steel

• Hydrogen embrittlement

High power channel-type reactor (Generation II)

Tinlet : 260 ◦ C, P: 8 MPa Toutlet : 290 ◦ C

• Cladding material: Zircaloy

• Hydrogen embrittlement, loss-of-coolant accident (continued)

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Table 6 (continued) Application/ system/ component

Temperature range

Service condition

Structural materials

Super critical water-cooled reactor (SCWR) (Generation IV)

Tinlet : 290 ◦ C, Toutlet : ~ 550 −600◦ C

P: 25 MPa, maintained above the thermodynamic critical point of water (T = 374 ◦ C, P = 22.1 MPa) Neutron spectrum: Thermal (Maximum dose: ~ 30 dpa) Neutron spectrum: Fast (Maximum dose: ~ 70 dpa)

Candidate • Microstructural cladding stability, materials: dimensional • Zr alloys, stability • Resistance to Austenitic stress corrosion stainless steel, cracking, F/M steels, irradiationNi–based assisted stress superalloys In-core: corrosion • Zr alloys, cracking • Creep resistance Austenitic under irradiation stainless steel, F/M steels, Ni–based superalloys, low-swelling stainless steels Out-of-core: • F/M steels, low alloy steels

P: 0.1 MPa Neutron spectrum: Thermal Maximum dose: 200 dpa

Candidate cladding materials: • F/M steels • ODS alloys In-core • FM ducts, 316SS grid • Plate Out-of-core: • Ferritic steel, Austenitic steel

• High dimensional stability • Irradiation resistance • Corrosion resistance • Creep resistance

Very low operating pressure (0.1 MPa) Toutlet : 800 ◦ C Neutron spectrum: Fast Maximum dose: 150 dpa

Candidate cladding materials • Austenitic stainless steel • F/M steels • ODS alloys • SiC • Refractory alloys Out-of-core: • High-Si F/M steel, refractory alloys, ceramics

• High dimensional stability • Irradiation resistance • Corrosion resistance • Creep resistance

Sodium-cooled Tinlet : ~ 370 fast reactor (SFR) ◦ C (Generation IV) Toutlet : ~ 550 ◦C

Lead-cooled fast reactor (LFR) (Generation IV)

Tinlet : ◦C

~ 600

Challenges

(continued)

Advanced High-Temperature Structural Materials …

97

Table 6 (continued) Application/ system/ component

Temperature range

Gas-cooled fast reactor (GFR) (Generation IV)

Very high-temperature reactor (VHTR) (Generation IV)

Service condition

Structural materials

Challenges

Tinlet : ~450 ◦ C P: 7 MPa Toutlet : ~850 Neutron spectrum: ◦C Fast Maximum dose: 80 dpa

Candidate cladding materials • ODS alloys • Refractory alloys • SiC In-core • Refractory metals and alloys, ODS, ceramics Out-of-core • Ni-based superalloys, F/M steels

• High dimensional stability • Irradiation resistance • Corrosion resistance • Creep resistance

Tinlet : ~600 ◦ C High-temperature, Toutlet : ~1000 low-pressure ◦C operation (P: 7 MPa) Neutron spectrum: Thermal Maximum dose: < 20 dpa

Core: graphite • Control rod: C/C Candidate cladding materials • Graphite • Ni-based superalloys • SiC or ZrC coating • Refractory alloys In-core: • Graphite, SiC, ZrC, Out-of-core: • Ni-based superalloys, F/M steels, low alloy steels

• High dimensional stability • Irradiation resistance • Corrosion resistance • Creep resistance

emerged as an attractive alternative for weight reduction. For example, General Electric (GE) estimated that ~6% of weight reduction is possible in GE90-115 engine owing to the incorporation of CMC turbine blades [44]. Recent advancement in additive manufacturing has paved the way for developing large components in a single-step processing [45]. For example, the additively manufactured fuel nozzles in the GE LEAP engine offer ~25% weight savings and simultaneously cause a drastic reduction of the number of parts to be assembled from 18 to 1 [43, 46]. Furthermore,

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Fig. 4 Schematic diagram of the graphite-moderated very high-temperature reactor (VHTR) (reproduced with permission from [27])

Fig. 5 An isometric section of a typical aero-engine showing important parts and components exposed to different temperatures and related challenges of material degradation during operation (reproduced with permission from [41])

Advanced High-Temperature Structural Materials …

99

Table 7 Summary of operating conditions, structural materials, and challenges in aero-engine [43] Application/ Temperature range Service system/ condition component Aero-engine • Combination of hightemperature and stress • Temperature of compressor may reach ~1370 ◦ C • Temperature of turbine blade may reach ~1500 ◦ C • For military jet engines, turbine temperature ~1590 ◦ C

Structural materials

Challenges

Corrosive • Fan: Al, Ti, or stainless steel • Resistance environment, • In GEnx engines, carbon to fatigue stress, and fibre-reinforced plastic (CFRP) and creep thermal composites are used in fan blades • Design of light• Low-pressure compressor: shock weight Ti-6Al-4 V or Ni alloy • High-pressure compressor: structure Ti-6Al-2Sn-4Zr-2Mo or Ni alloy with • Combustion chamber: Ni- or improved Co-based superalloys corrosion • High-pressure turbine: resistance Ni-based superalloy and • Low-pressure turbine: reduced Ni-based superalloy emission • Exhaust nozzle: Ni, Inconel, of CO2 and stainless steel with • Casting: Al and polymer matrix enhanced composite tempera• Accessories section: Al or Fe ture alloy capability • Shaft: Stainless steel, Ti-6Al-4 • Reduce V, Ni-based superalloy, and fuel Cr–Mo-V steels consumption

the fuel efficiency of LEAP engines is about 15% higher than that of CFM56 engines [46].

3.5 Spacecraft Thermal Protection System Thermal protection system (TPS) is one of the most crucial parts of a space vehicle as the former is responsible for protecting the space shuttle from aerothermal heating during atmospheric re-entry. Over the years, many different types of thermal protection systems (active, semi-passive, and passive) [47] have been developed, several of which have successfully served both unmanned and manned space missions. Table 8 summarizes the operating conditions, varieties of structural materials used in TPS, and major challenges that put forward the need of developing advanced thermal protection systems for reusable launch vehicles. Figure 6 presents an overview of different heat-resistant tiles that constitute the TPS of a space vehicle [48]. SiC-coated reinforced carbon–carbon composite (RCC, ρ =√1.6–1.98 g/cm3 , elastic modulus: 40–100 GPa, and fracture toughness: 5–10 MPa. m), which has the capability to withstand extremely high temperatures (~2400 ◦ C), find application

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Table 8 Service condition, structural material, and challenges of space shuttle thermal protection system [48, 55, 171] Application/ system/ component

Service condition

Structural materials

Challenges

Thermal protection system

Exposure to very high temperature ~1650 ◦ C, Extreme harsh condition during re-entry into earth’s atmosphere. For example, • Leading edge (heat flux ∼20–85 W/cm2 , temperature ∼1130–1700 K) • Nose cap (heat flux ∼68 W/cm2 , temperature ∼1540 K) • Windward region (heat flux ∼13–30 W/cm2 , temperature ∼1000–1370 K) • Leeward region (heat flux ∼6 W/cm2 , temperature ∼800 K) • Twin vertical tail (heat flux ∼123 W/cm2 , temperature ∼2050 K)

• Nose cap: Reinforced carbon–carbon (RCC) • Leading edge: SiC-coated C/C • Orbiter underside: High-temperature reusable surface insulation (HRSI) tile, Fibrous refractory composite insulation (FRSI) • Windward: Silica tiles • Leeward: Flexible external insulation (FEI) • Upper fuselage: Low-temperature reusable surface insulation (LRSI) tile • Mid fuselage and fuselage side: Felt reusable surface insulation (FRSI) • High-temperature areas: Toughened unipiece fibrous insulation (TUFI) tile

• Strike of debris • Puncture of RCC and other tiles • Design of TPS for next-generation space vehicles where re-entry temperature will reach ~2000 ◦ C • Development of oxidation- and ablation-resistant materials for nose cone and sharp leading edges of next-generation space vehicles

Fig. 6 An overview of various types of heat-resistant tiles used as thermal protection system in different parts of space re-entry vehicle (reproduced with permission from [48])

Advanced High-Temperature Structural Materials …

101

in nose cone and wing leading edges, since the most intense heat flux is encountered in those sections. In 2015, NASA identified three major areas in which R&D efforts are likely to take place in the next few decades [49]. These include the following: (i) design of TPS which can effectively withstand high heat flux (>5000 W/cm2 ) and re-entry velocity (>11 km/s), (ii) modelling and simulation, and (iii) development of advanced sensors for TPS.

4 High-Temperature Structural Materials This section provides an outline of different structural materials used in various engineering sectors as mentioned in Sect. 3. At the outset, Sect. 4.1 highlights the importance of steel as a high-temperature structural material. Section 4.2 reveals the application and maximum service temperature of various Ti alloys. Sections 4.3 and 4.4 summarize the recent developments of maraging steels and intermetallics, respectively. The progress of superalloys and refractory metals is narrated, respectively, in Sects. 4.5 and 4.6. Lastly, Sects. 4.7 and 4.8 present a brief overview of carbon-based materials, ceramics, and composites.

4.1 Steel Despite significant advancement in various high-temperature structural materials with high specific strength, till date, steel continues to serve as the prime and most reliable structural material in the low and medium temperature range in numerous structural engineering applications [50, 51]. For example, austenitic stainless steel finds application in jet engines, rotor of steam turbines, and gas turbines due to its excellent tensile strength, moderate corrosion resistance, creep strength, fatigue strength, and heat resistance up to 650 ◦ C. In spite of excellent yield strength (550– 690 MPa), duplex stainless steels are not prescribed for applications at a temperature higher than 300 ◦ C due to possibilities of embrittlement and loss of toughness at high temperature. High-temperature steels with a high yield strength (1500–2000 MPa), high elastic modulus, and fatigue strength, which can retain mechanical properties up to 300–450 ◦ C, are preferred for heavily loaded aircraft structures in wing-root attachments, slat track components, landing gears, engine pylon, etc. [52]. On the other hand, medium-carbon (0.25–0.50 wt.% C) low alloy steels containing Ni, Cr, Mo, V, and Co are materials of choice for the undercarriage part of the aircraft. Table 9 summarizes the chemical composition of various steels and their respective maximum service temperature (in air). Salient features of different steels used in the petroleum industry are summarized in Table 10 [11]. Figure 7a exhibits the variation of yield strength of different AISI steels with temperature showing that AISI 309 offers the best yield strength at 800 ◦ C compared to its counterparts. The variation

0.15

0.12

0.08

0.20

0.25

0.08

0.08

0.08

430

304

309

310

316

321

347

C

2.00

2.00

2.00

2.00

2.00

2.00

1.00

1.00

Mn

0.045

0.045

0.045

0.045

0.045

0.045

0.04

0.04

P

0.03

0.03

0.03

0.03

0.03

0.03

0.03

0.03

S

Chemical composition (wt.%)

410

AISI Type

1.00

1.00

1.00

1.50

1.00

1.00

1.00

1.00

Si

17/19

17/19

16/18

24/26

22/24

18/20

16/18

11.5/ 13.5

Ni

9/13

9/12

10/14

19/22

12/15

8 /10.5

–

–

N

–

–

2.0/ 3.0

–

–

–

–

–

Mo

–

–

5xC (min)

–

–

–

–

–

Ti

10xC (min)

–

–

–

–

–

–

–

Nb + Ta

Table 9 Chemical compositions and maximum service temperature of various steels [53]

Balance

Balance

Balance

Balance

Balance

Balance

Balance

Balance

Fe

870

870

870

1035

980

870

870

815

Intermittent service

925

925

925

1150

1095

925

815

705

Continuous service

Max. service temp. in air (◦ C)

102 P. Sengupta and I. Manna

17.0

22.0

25.0

316SS

22Cr

25Cr

7.0

5.0

12.0

0.8 0.20 –

2.0 0.08 –

Fe

P

S

Si

Ta

Characteristics

balance –

balance –

4.0 1.0 0.10 0.30 balance –

–

–

–

–

–

–

–

–

–

–

–

–

balance 0.045 0.03 0.75 8(C + N) min to 1.00 max

Corrosion resistance in H2 S/CO2 environment (in absence of S)

Localized corrosion in presence of H2 S and O2

Ideal for oil field application where O2 is absent

Corrosion resistance in CO2 /NaCl environments in the absence of H2 S and O2

balance 0.045 0.03 0.75 10(C + N) min to Excellent resistance to general corrosion and 1.00 max intergranular corrosion

3.0 1.0 0.10 0.10 balance –

2.5 1.0 0.04 –

–

13.0

13Cr

9–13

17.0–19.0 9.0–13.0 –

N

2.0 0.08 –

Mo Mn C

347H

Ni

17.0–19.0 9.0–13.0 –

347

Cr

Alloy Grade Composition (wt. %)

Table 10 Salient features of different steels used in petroleum industry [11]

Advanced High-Temperature Structural Materials … 103

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P. Sengupta and I. Manna

Fig. 7 a Temperature dependence of yield strength, b stress level needed for 1% creep strain in 10,000 h, and c the same for 100,000 h of creep for different types of stainless steels (data adapted from Table of Ref. [53])

of stress at creep rate of 1% at 10,000 h and 100,000 h is presented in Fig. 7b, c, respectively [53]. It is worth mentioning that the structural materials used in today’s supercritical power plants will not suffice to serve for AUSC technology. Hence, it is important to design materials that will exhibit superior creep resistance, oxidation resistance, and better resistance to sulphur attack, compared to currently used stainless steels in supercritical boilers. It is obvious to note that 9-12Cr steels fail to serve a temperature of 700 ◦ C due to rapid reduction in strength with temperature. In addition to that, various advanced austenitic grade steels (e.g., super 304H, 347 HFG, NF 709, etc.) fail to retain the minimum desired strength of 100 MPa up to 700 ◦ C. However, various Ni-based alloys (e.g., Haynes 230, Haynes 282, Std. 617, Inconel 740/ 740H, etc.) can retain the required strength at the service temperature necessitated in AUSC technology. As a structural material of fluid-cooled furnace walls of boiler, the American Society of Mechanical Engineers (ASME) has approved alloy T92 (9Cr Mo W) as high-strength martensitic boiler material. High-strength 2¼CrMoW alloy (T23) is also another promising material for such application. On the other hand, various Nibased alloys are recommended by ASME for application in reheater and superheater tubes. Owing to superior resistance to pitting corrosion and stress corrosion cracking in Cl − containing environments, stainless steels find application in the petroleum industry [51]. AISI 304L stainless steels are used as structural materials of containers designed for storing medium-level radioactive waste generated by the nuclear industry [54]. AISI 304 and AISI 316 austenitic stainless steels are used as structural materials in fast breeder reactors [51]. Table 6 summarizes the salient features of different nuclear fission reactors [55]. For the core structures of lead-cooled fast reactor (LFR), sodium-cooled fast reactor (SFR), high-temperature gas-cooled reactor (HTGR), and super critical water-cooled reactor (SCWR), 9–12% Cr-based ferritic-martensitic (FM) steel and oxide dispersion-strengthened (ODS) steels are considered [56, 57]. A533 Grade B Class 1 and A508 Grade 2/3 Class 1 Light water reactor (LWR) vessels are clad with stainless steel in order to prevent contamination of coolants from the corrosion products. Since ferritic-martensitic steels exhibit superior void-swelling phenomenon compared to conventional austenitic steels, various

Advanced High-Temperature Structural Materials …

105

FM grade steels (12Cr-1MoVW, 9Cr-1Mo, duplex 9Cr-2MoVNb, 11Cr-MoVNbW, 12CrMoVNb, etc.) were envisaged as structural materials for selecting the core material of fast reactor in different countries [58]. In addition to the above, ferriticmartensitic (FM) steels are also envisioned as potential structural materials for core components of nuclear reactors like Prototype Gen-IV sodium-cooled fast reactor (PGSFR), China-Fast Reactor 1000 (CFR 1000), BN-1200, etc. [59, 60]. The total elongation of different grades of FM steels (9 Cr (EM10, T91), 11Cr, 12Cr, ORNL9Cr, JLF-1, LA12LC, OPTIFER, EUROFER97, F82H) with respect to the neutronirradiation temperature in material test reactors (MTRs) are extensively investigated by researchers [33, 61–64]. The total elongation offered by reduced activation FM (RAFM) steels is found to be within an acceptable level, even at a very high neutronirradiation dose of 80 dpa [58]. The volumetric swelling and void swelling of different grades of FM steels as a function of neutron-irradiation dose (dpa) elucidate that swelling rates of ≤0.012%/dpa were shown by HT9 and 9Cr-1Mo steels even when the irradiation dose was as high as 208 dpa at 400 ◦ C [65]. Different grades of RAFM steels like JLF and F82H offered volumetric swelling behaviour compared to the swelling of commercial FM steels like EM10 and EM12. Several factors that contribute towards superior swelling behaviour of 9Cr and 12Cr FM steels include the following: low dislocation-bias, high self-diffusion, formation of different precipitates (M23 C6 , MX), high dislocation density, defect annihilation sites, martensitic microstructure, etc. [62, 66–69]. The variation in hoop deformation behaviour in FM and ODS steel is exhibited as a function of displacement dose which revealed that FM steels and ODS steels offer superb corrosion resistance as well as swelling resistance, compared to 15/15TI, AISI 316L, and 316TI grade steels. The swelling behaviour gets enhanced in austenite grade steels at a displacement dose of 70 dpa or more [34]. In recent years, co-precipitation of nanoscale particles (example: Cu, Mo2 C, NbC, B2-NiAl, η-Ni3 Al, Ni2 AlTi, L21 -Ni2 AlMo, etc.) has led to the evolution of ultrahigh-strength steel with a unique combination of tensile properties, creep resistance, irradiation resistance, and weldability [70, 71]. B2-NiAl nanoparticle-strengthened Fe–Ni-Al ferritic steels exhibit a good combination of thermal conductivity and oxidation resistance. Consequently, these steels are suitable for high-temperature structural applications [71–73]. From Fig. 8, it is evident that NiAl/Ni2 AlTistrengthened steels offer improvement in creep resistance at 700 ◦ C, compared to T91, T122, 12Cr, P92, and P122 grade steels. First principle atomistic simulation approaches like DFT (Density Functional Theory) calculations and thermodynamic analysis have played a crucial role in designing ultra-high-strength steel [71].

4.2 Ti Alloys Figure 9 exhibits 0.2% yield strength and tensile strength of Ti alloys of various grades. Due to relatively low density, high specific strength, high specific stiffness, creep strength, fracture toughness, prolonged fatigue life, ability to retain

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P. Sengupta and I. Manna

strength up to 500–600 ◦ C, and in addition, very high resistance to exfoliation, stress corrosion cracking, and oxidation, Ti alloys have emerged as a crucial engineering material, which has wide-spread application in critical areas (shafts, fan blades, low-pressure compressors, casings, nozzle assemblies, etc.) of gas turbine engines [74]. In general, Ti alloys are widely used in ducts, manifolds, engine frames, except in the hot sections of the combustion chamber, where the operating temperature exceeds 600 ◦ C. Table 11 shows the chemical composition and maximum service temperature of various popular grades of Ti alloys [75]. In commercial aircrafts, Ti alloys are used in wings, wing boxes, and undercarriage parts. As a matter of fact, the total structural weights of Ti alloys in A380 and B777 commercial aircrafts is ~10% and ~9%, respectively [74]. Similarly, β-Ti alloys (Ti-5Al2Zr-2Sn-4Cr-4Mo, Ti-6Al-2Sn-4Zr-6Mo) find application in fan discs of commercial gas turbine engines since the use of these alloys contributes to overall weight reduction by about 25%. Ti-6Al-4V alloy is the most commonly employed alloy for airframes, jet engines, and biomedical applications [48, 76, 77]. On the other hand, for military aircrafts, Ti alloys account for nearly 10–30% of their total structural weight. For example, F-15 Eagle and F-14 Tomcat supersonic military aircrafts utilize nearly 26 wt% of Ti alloys in crucial parts like landing gear, hydraulic tubing, highly stressed wings, tail sections, fuselage skins, firewalls, engine pod frames, and wing torque box. In addition to that, Ti alloys find application in blade tips, main rotor hubs, clamps, pivots, tail rotor hub, etc. In rockets, Ti alloys are used in fuel storage tanks, fuel engines, high-pressure gas storage tanks, etc. However, Ti and its alloys suffer several disadvantages as well. Firstly, the density of Ti (ρ = 4.5 g/cm3 ) is higher than that of Al (ρ = 2.7 g/cm3 ) and carbon composites (ρ ∼1.5– 2 g/cm3 ). Secondly, Ti is costlier than steel and other commonly used structural materials. Thirdly, machining of Ti alloys is not easy, and hence, it is difficult to produce components with complex geometry and intricate shape in conventional processing. Recent development in additive manufacturing has paved the ways to solve the issues pertaining to processing of Ti alloys with complex geometry [78].

4.3 Maraging Steel Owing to the excellent strength (1500–2300 MPa), fracture toughness, and ductility, maraging steels (with C < 0.03 wt.%) find applications in heavily loaded components in aircraft structure. Table 12 presents salient features of maraging steels, mediumcarbon low alloy steels, and precipitation-hardened stainless steels used in aircraft. Maraging steels are potential candidates for application as high-strength and high-performance structural materials. The extremely high strength of maraging steels is primarily due to the semi-coherent ultrafine intermetallic precipitates. Many a time, the coherency strain leads to the initiation of crack under applied load. Researchers have successfully developed Ni(Al,Fe)-strengthened maraging steels with the excellent combination of strength and ductility. Figure 10a exhibits an

Advanced High-Temperature Structural Materials …

107

Table 11 The chemical composition and maximum service temperature of various Ti grades [75] Ti alloy grade

Composition (wt.%)

Developed Maximum by service temperature (◦ C)

Ti-6Al-4 V

Ti-6Al-4V

USA

BT6

Ti-6Al-4.5V

Russia

Ti17

Ti-5Al-2Sn-2Zr-4Mo-4Cr

USA

Ti811

Ti-8Al-1Mo-1V

USA

Ti6246

Ti-6Al-2Sn-4Zr-6Mo

USA

Ti6242

Ti-6Al-2Sn-4Zr-2Mo

USA

BT3-1

Ti-6.5Al-2.5Mo-0.3Si-1.5Cr-0.5Fe

Russia

TC6

Ti-6Al-2.5Mo-0.3Si-1.5Cr-0.5Fe

China

BT8M-1

Ti-5.5Al-1Sn-1Zr-4Mo-0.16Si

Russia

IMI550

Ti-4Al-2Sn-4Mo-0.5Si

UK

IMI679

Ti-2.25Al-11Sn-5Zr-1Mo-0.25Si

UK

BT8

Ti-6.5Al-3.5Zr-0.2Nb-0.16Si

Russia

TC9

Ti-6.5Al-2.5Sn-3.5Mo-0.3Si

China

TC11

Ti-6.5Al-1.5Zr-3.5Mo-0.3Si

China

IMI685

Ti-6 Al-5Zr-0.5Mo-0.25Si

UK

Ti6242S

Ti-6Al-2Sn-4Zr-2Mo-0.1Si

USA

Ti5621S

Ti-5Al-6Sn-2Zr-1Mo-0.25Si

USA

IMI829

Ti-5Al-3.5Sn-3Zr-0.27Mo-0.3Si-1Nb

UK

BT9

Ti-6.5Al-2Sn-3.5Mo-0.3Si

Russia

BT25

Ti-6.8Al-2Sn-1.7Zr-2Mo-0.2Si

Russia

BT25Y

Ti-6.5Al-2Sn-4Zr-4Mo-0.2Si-1W

Russia

Ti55

Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd

China

Ti633G

Ti-5.5Al-3.5Sn-3Zr-0.3Mo-0.3Si-1Nb-0.2Gd

China

Ti53311S Ti-5.5Al-3.5Sn-3Zr-1Mo-0.3Si-1Nb

China

TA12

Ti-5.5Al-4.5Sn-2Zr-1Mo-0.3Si-1Nd

China

Ti1100

Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si

USA

IMI834

Ti-5.5Al-4Sn-4Zr-0.3Mo-0.5Si-1Nb-0.06C

UK

BT36

Ti-6.2Al-2Sn-3.6Zr-0.7Mo-0.15Si-5 W

Russia

Ti60

Ti-5.8Al-4.8Sn-2Zr-1Mo-0.35Si-0.85Nd

China

Ti600

Ti-6Al-2.8Sn-4Zr-0.5Mo-0.4Si-0.1Y

China

Ti65

Ti-5.9Al-4Sn-3.5Zr-0.3Mo-0.4Si-0.3Nb-2Ta-1W-0.05C

China

300−400

400−500

450−500

500−550

550−600

600−650

108

P. Sengupta and I. Manna

Fig. 8 Comparative creep behaviour of nano-precipitate-strengthened P92, P122, T91, T122, and 12Cr structural steels at 700 ◦ C (reproduced with permission from [71])

engineering stress–strain diagram of Fe-18Ni-3Al-4Mo-0.8Nb-0.08C-0.01B (wt.%) maraging steel which confirms that the aged (500 ◦ C for 3 h) steel offers much higher strength (UTS: 2197 ± 33 MPa) and ductility (8.2 ± 0.7%) compared to the solution-annealed steel (950 ◦ C for 15 min). Furthermore, the yield strength of the as-aged Ni(Al, Fe) maraging steel is ~1.1 GPa, which is significantly higher than that of solution-annealed maraging steel. Figure 10b, c represents STEM images of solution-annealed and aged maraging steels. The presence of high dislocation density is observed in Fig. 10b. On the contrary, uniform precipitation of spherical Ni(Al, Fe) nano-sized precipitates is observed in Fig. 10c. The remarkable combination of strength and ductility could be achieved due to the homogeneous distribution of coherent nanometric precipitates with minimal lattice misfit as Ni(Al, Fe) nano-precipitates prevent the crack initiation at the interface [79]. Among maraging steels, GE1014 offers excellent combination of high toughness and fatigue strength (~2200 MPa) and hence find applications in the shafts of GE90-115B and GEnx engines [40]. Recently, several research groups have reported creep-resistant maraging steel for prospective application in low-pressure turbine shafts of modern jet engines [80, 81]. Sun et al. [82] developed Fe-9.9Cr-8.02Co-6.99Ni-1.8Al2.75Mo-2.43 W (wt.%) maraging steel with creep fracture life of 2148 h at 500 ◦ C under applied stress of 700 MPa. The excellent creep rupture life was ascribed to the formation of nanoscale precipitates of β-NiAl and Laves phases [82].

0.03 18 (max)

0.03 18 (max)

0.03 18 (max)

18 Ni (250)

18 Ni (300)

18 Ni (350)

– –

0.3 – 4.5 – 4

0.38

0.25

0.35

Aermet 100

H11

Precipitation-hardened 15−5PH 0.07 steels 17−4PH 0.07

11

0.4

–

1.5

13.5 1.2

1.8 –

0.2

Al

Cr

–

–

–

–

–

–

–

–

–

–

–

–

–

0.5

–

–

–

–

16

15

5

3

1

1

0.4

–

0.8 0.8

–

–

–

–

Cu

1

1

1

–

1.6

4

–

–

–

–

–

–

Nb

0.45

–

–

660

540 410

Balance 1650

Balance 1720

Balance 1590

Balance

Balance

Balance 2300

Balance 1950

Balance 1700

Balance

Fe

–

Balance 1150

1330

1470

2000

1960

1930

750

700

2370

2000

1790

970

10

10

9

14

7

22

25

6

9

11

17

Yield Ultimate Elongation strength tensile (%) (MPa) strength (MPa)

0.3 Balance 1400

–

0.05 – (min)

–

–

–

–

–

–

V

3.5 –

–

–

–

0.25 –

0.25 –

–

–

–

–

Mn Si

0.8 0.7

1

1.6 0.1 –

0.7 0.1 –

0.4 0.1 –

0.2 0.1 –

Ti

0.25 –

300 M

–

0.4

1.8 –

0.3

4340

–

5

5

3.3

Mo

12.5 4.2

9

8.5

8.5

Co

4130

Medium-carbon low alloy steel

0.03 18 (max)

18 Ni (200)

Ni

Maraging steel

C

Chemical composition (wt.%)

Type

Steels

Table 12 Chemical composition, yield strength, ultimate tensile strength, and % elongation of different steels used as structural materials in aircraft [52]

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4.4 Intermetallics Over the years, several useful research studies have been carried out to develop Ni– Al, Ti–Al, Fe–Al, Nb–Al, and Be-based standalone intermetallic alloys (single or multiple phase or compound) for prospective high-temperature structural and coating applications [83–88]. However, the major limitation of intermetallics includes relatively poor ductility and brittleness, which can be mitigated to some extent by suitable alloying addition. Table 13 provides an overview of different intermetallics. Ni3 Al (ordered L12 )-based intermetallic compounds have potential application in cutting tools, furnace fixtures, turbocharger rotors, and turbine blades for enhanced fatigue life and excellent creep strength [84]. Although NiAl (ordered B2) offers excellent creep strength and environmental durability, its relatively poor ductility limits structural applications [89]. Owing to the extensive research work, γ -TiAl has found application in the aircraft engine and automobile industry [90, 91]. Figure 11a exhibits representative bright-field TEM image of oil quenched Ti-45Al-7.5Nb displaying ultrafine lamellar structure which comprises of γ −T i Al/α2 −T i 3 Al phases [92]. The comparison of temperature dependence of specific Young’s modulus of γ -TiAl with other high-temperature structural materials (IMI 834, IN 625, IN 718) is presented in Fig. 11b. It is worth noting that γ -TiAl offers an excellent combination of density, high melting point, excellent strength, oxidation resistance, very good creep properties, and ease of processing [89–91]. Compared to α2 alloys (~22–35 at.% Al), two-phase γ -TiAl alloys are preferred for higher temperature application since the latter offers better high-temperature oxidation resistance. Another important intermetallic that has received extensive research attention is iron aluminide [83, 86, 93]. Driven by several factors like the abundance of lowcost Fe, ease of fabrication, excellent oxidation, and hot corrosion resistance, several research groups have explored iron aluminides for high-temperature structural applications [83, 86, 94]. However, limiting factors like poor ductility, hydrogen embrittlement, and low creep strength have restricted such aspiration [95, 96]. In recent years, Table 13 The melting temperature, density, elastic modulus, and maximum service temperature of different intermetallic compounds [85] Intermetallic

Melting temperature (◦ C)

Density (g/cm3 )

Elastic modulus (GPa)

Maximum service temperature Strength (◦ C)

Corrosion (◦ C)

Ni3 Al

1380

7.50

179

1000

1150

NiAl

1640

5.86

294

1200

1400

Fe3 Al

1540

6.72

141

600

1100

FeAl

1250

5.56

261

800

1200

Ti3 Al

1600

4.20

145

760

650

TiAl

1460

3.91

176

1000

900

MoSi2

2020

6.24

440

–

–

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Table 14 The yield strength, ultimate tensile strength, flexural strength, fracture toughness, creep limit, and oxidation limit of different intermetallic compounds [85] Intermetallics

Yield strength (MPa)

UTS (MPa)

Flexural strength (MPa)

Fracture Creep Oxidation toughness limit limit (◦ C) √ (MPa. m) (◦ C)

Ti3 Al

700−990 800−1140 –

–

760

650

TiAl

400−650 450−800

–

–

1000

900

MoSi2

–

–

140–160

2.5−5.0

1300

1700

Mo3 Si

–

–

–

3.0

1300

1000

Mo5 SiB2

–

–

–

2.0

1500

1400

Mo–Si–B – (Mo-Mo3 Si–Mo5 SiB2 )

–

400–600

5−20

1400

1300

Nb–Nb5 Si3

–

–

500–1450 6−24

1200

1200

Nb–Si multicomponent – alloy

–

800–950

1200

1300

18.2−23.3

iron aluminide is being explored as a coating material for crucial engineering applications that need superb resistance to oxygen and sulphur attack at elevated temperatures (~700 ◦ C) in advanced ultra-supercritical thermal power plants [87, 97]. Al-rich trialuminides (Al3 X type), based on Al–Ti–Mn, Al–Ti–Cr, Al–Ti–Ag, Al–Ti–Ni, and Al–Ti–Fe ternary systems, are also attractive choices for high-temperature applications since they offer excellent oxidation resistance and remarkable creep properties [89]. Similar to other intermetallics, the poor ductility of trialuminides hinders their structural applications. Table 14 enlists the mechanical properties and oxidation limit of various intermetallics and alloys.

4.5 Superalloys Over the years, superalloys have consolidated their candidature as high-temperature structural materials due to their unique combination of oxidation and creep resistance [98, 99]. In advanced aircraft engines, the cumulative weight of components made of superalloys accounts for ~50% of the engine’s total weight [43]. Table 15 shows the chemical compositions of some Ni-based superalloys. In this context, it is imperative to mention that the microstructure of typical single crystal Ni-based superalloy elicits the coexistence of two distinct phases, namely fcc Ni (bright) and L10 Ni3 Al (dark). Several alloying elements like Cr, Al, Ti, B, Zr, Nb, Re, Ta, W, Mo, and Hf are added to Ni-based superalloys to enhance the oxidation resistance and corrosion resistance and improve the solid solution strengthening. In Ni-based superalloys, the  coherent γ -(Ni, Co)3 (Al, Ti, Ta) intermetallic (ordered L12 structure) phase [100] acts as a barrier to the movement of dislocations, thereby enhancing the strength of these alloys. In addition, the formation of the in-situ γ  -Ni3 Nb (body centred

Balance

Balance

Balance

Balance

Balance

Balance

Balance

CMSX-10

TMS-138

TMS-138A

TMS-162

TMS-173

TMS-238

Balance

CMSX-4 Plus

CMSX-8

Balance

Ni

6.5

5.6

5.8

5.8

5.8

3.0

10.0

10.0

9.0

Co

5.8

3.0

3

3.2

3.2

2.0

5.4

3.5

6.5

Cr

Chemical composition

CMSX-4

Alloy

Mo

1.1

2.8

3.9

2.8

2.8

0.4

0.6

0.6

0.6

Re

6.4

6.9

4.9

5.8

5.0

6.0

1.5

4.8

3.0

Ru

5.0

5.0

6

3.6

2.0

–

–

–

–

W

4.0

5.6

5.8

5.6

5.9

5.0

8.0

6.0

6.0

Al

5.9

5.6

5.8

5.7

5.9

5.7

5.7

5.7

5.6

Ti

–

–

–

–

–

0.2

0.7

0.85

1.0

Ta

7.6

5.6

5.6

5.6

5.6

8.0

8.0

8.0

6.5

Nb

0.1

–

–

–

–

0.1

–

–

–

Hf

–

0.10

0.10

0.10

0.10

0.03

0.2

0.1

0.1

Temp.

Stress (MPa)

392 137

1150

137

137

137.2

137.2

137

190

190

190

900

1100

1100

1100

1100

1100

1050

1050

1050

(◦ C)

Test parameter

Creep rupture life

Table 15 Typical compositions (wt.%) and creep rupture life of various Ni-based superalloys [98, 102–105]

124 (predicted), 94 (observed)

1306

1137

959

722.4

412.3

220

81

231

90

Life (h)

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tetragonal) also strengthens the Ni-based superalloys. Currently, turbine blades are made of Ni-based superalloys (single crystal), which are coated with thermal barrier coating (TBC) like yttria-stabilized zirconia top coat to improve its temperature capability. The static components of turbine like engine shafts are primarily made of polycrystalline Ni-based superalloys and high-strength steels. However, the quest of increasing the turbine inlet temperature for improved performance and efficiency has posed a challenge to the materials community to design and develop new materials for high-pressure turbine sections. In this context, it is important to mention that Ni-based single crystal superalloys can sustain temperature up to 1100–1200 ◦ C, which is ~0.9 of Tm (where Tm presents the melting temperature in absolute scale) [43, 101]. There is continued research effort to develop bond coats and ceramic top coats for enhanced temperature capability of these alloys. Figure 12a shows the representative microstructure of Ni-based superalloy eliciting the presence of fcc Ni and L12 Ni3 Al. If we review the composition of Ni-based superalloys (Table 15), it will be evident that a significant amount of Re, Ru, W, and Ta is used in these alloys [98, 102–105]. For example, TMS-238 superalloy contains 6.4% Re, 5% Ru, 4% W, and 7.6% Ta; these alloying elements are crucial for enhancing the creep resistance and high-temperature strength of these alloys. Recently, Wu et al. [106] have documented that addition of ~3 wt.% Re is capable of increasing the creep life of Ni-based superalloys by almost two times. However, the supply risk, sudden price fluctuation, and volatility in the market are the major constraints faced by the manufacturers. In order to mitigate such problems, several research groups are exploring alternative materials which can potentially replace the traditional Ni-based superalloys. It is established that Co-based alloys can offer the flexibility to increase the turbine inlet temperature to ~100–150 ◦ C, compared to Ni-based superalloys. Solid solution-strengthened Nb-based alloys (Nb-19Ti-4Hf13Cr-2Al-4B-16Si, at. %) have emerged as a potential candidate since they offer low density (ρ = 8.56 g/cm3 for pure Nb, compared to 8.90 g/cm3 for pure Ni), better toughness, and better creep resistance and oxidation resistance [107]. Similarly, solid solution-strengthened Mo-Si-B alloys offer a good combination of strength, oxidation resistance, and creep resistance [101, 108–110]. In addition to the solid solutionstrengthened bcc Mo phase, the presence of MoSi3 (T1) and Mo5 SiB2 (T2) is noticed in these alloys. TEM image of Co-Al-W alloy (Fig. 12b) shows the presence of Co3 (Al, W) precipitates embedded in solid solution-strengthened Co [43]. Figure 13 exhibits the variation of yield strength and 100 h rupture strength of various Ni-based superalloys with temperature. Owing to the strengthening by ordered precipitates (γ  ), γ /γ  Co-based superalloys offer remarkable high-temperature strength compared to solid solution-strengthened Co-based superalloys. Figure 14 shows the variation of 0.2% yield strength of Co–Al–W-based superalloys and commercial Ni-based superalloys. It may be observed that, despite initial reduction of yield strength up to 600 ◦ C, Co-Al-W-Ta superalloy offers yield strength superior to Waspaloy at 870 ◦ C [111]. Due to precipitation of W/Co boride phase on grain boundary and segregation of B/Zr, the polycrystalline Co-Al-W superalloys exhibit excellent creep properties [112]. However, the presence of W invariably increases the density (ρ >

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Fig. 9 0.2% yield strength and tensile strength of Ti alloys of various grades (data adapted from [74])

9.5 g/cm3 ) of Co-Al-W-based superalloys. Several research groups have, therefore, continued research efforts in developing alternative Co-based superalloys [112–116]. In 2015, Makineni et al. [117] reported W-free Co–10Al–5Mo–2Nb superalloy with γ /γ  microstructure, where the composition of γ  phase was found to be Co3 (Al, Mo, Nb). The variation of 0.2% yield strength with temperature illustrates that Cobased multicomponent superalloys like Co–Al–Mo–Ta and Co–Ni–Al–Mo–Ta–Ti offer superior yield strength compared to conventional Co–Al–W-based superalloy [111]. Studies indicate that the addition of Ta, Ti, and Nb enhances the γ  solvus temperature of Co-based superalloys [111, 116–118]. In a recent study, Pandey et al. [119] reported that the addition of Re in Co–Ni–Al–Mo–Nb superalloy has effectively reduced γ /γ  lattice misfit and enhanced the stability of microstructure up to 900 ◦ C. Of late, several new superalloys based on Co–Al–V and Co–Ta–V, Co– Al–Ta are being explored with the objective of increasing the solvus temperature and improving the mechanical properties of these alloys [120–122]. The advent of machine learning has substantially accelerated the material development process. With the help of machine learning, recently, Liu et al. [115] have successfully synthesized Co–36Ni–12Al–2Ti–4Ta–1W–2Cr superalloy with high γ  solvus temperature (1266.5 ◦ C).

4.6 Refractory Metals Table 16 summarizes the crystal structure, density, melting points, tensile strength, elastic modulus, coefficient of thermal expansion, and thermal conductivity of commonly used refractory metals [5, 123, 124]. Owing to the extremely high melting point, refractory metals could have been the ideal choice for high-temperature structural applications. However, these elements undergo rapid oxidation much below their equilibrium melting point and there is a competing process between oxidation and volatilization of refractory metal oxides as those oxides exhibit much less fusion point compared to that of the corresponding base metal. Consequently, these alloys

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Fig. 10 a Engineering stress–strain diagram in as-solution-annealed and as-aged conditions, and corresponding STEM images in b as-solution-annealed and c as-aged conditions of maraging steels (reproduced with permission from [79])

Table 16 Crystal structure, density, melting points, tensile strength, elastic modulus, coefficient of thermal expansion, and thermal conductivity of commonly used refractory metals [5, 123, 124] Element

Crystal structure

Density (g/cm3 )

Elastic modulus (GPa)

Coefficient Thermal of thermal conductivity expansion (W/mK) (×10–6 /◦ C)

Nb

BCC

2468

Mo

BCC

10.3

2617

275

105

7.3

53.7

630

320

4.9

Ta

BCC

16.7

142

2966

205

185

6.5

54.4

Re

HCP

W

BCC

2.1

3180

1070

463

6.2

48

19.3

3410

960

400

4.5

155

8.58

Melting point (◦ C)

Tensile strength (MPa)

lose strength at intermediate or high-temperature ranges and are unsuitable for structural application in an oxidizing environment. Over the past few decades, extensive research has yielded new possibilities of structural application of refractory alloys and compounds, especially in the form of some intermetallic compounds [125–130]. Nb-Si refractory alloys offer very good mechanical properties at low as well as high temperatures [107, 131]. Nb–Mo–W–Ti–Si multicomponent alloy offers an excellent combination of compressive strength (650 MPa at 1498 ◦ C) and creep strength (1.4x10−7 s−1 at 1398 ◦ C under stress of 200 MPa) [110]. Nb- and Mo-based refractory alloys, due to low density and high melting point, have the potential to serve up to 1300 ◦ C and 1200 ◦ C, respectively [89]. Nb-RM-RE-IE-based multicomponent Nb alloys offer excellent high-temperature properties where RM, RE, and IE respectively represent refractory metal (Mo, W, V, Ta), rare earth elements (Zr, Hf, etc.), and interstitial elements (C, N, O, etc.) [132]. Owing to the excellent creep behaviour of Nb5 Si3 (melting point: 2515 ◦ C, ρ = 7.14 g/cm3 ) and Mo5 Si3 (melting point: 2180 ◦ C, ρ = 8.26 g/cm3 ), Nb-silicide- and Mo-silicide-based refractory alloys have received great research attention in recent years [132–134]. Of late, Mo-Si-B-based alloys have also received special attention from the scientific community [108, 109,

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135–137]. Refractory metal complex concentrated alloys (RCCAs) like NbMoTaWV and NbMoTaW are capable of retaining compressive yield stress up to 1600 ◦ C [132, 138]. Figure 15a shows the creep rate (ln ε˙ ) of Nb–18Si–5Hf and Nb–20Si-based alloys [132]. Figure 15b exhibits the experimentally determined creep rate of Nb– Si, Nb–Ti, and Nb–TM–Si–RM-based alloys at 1200 ◦ C under an applied load of 170 MPa. It is reported that the creep rate of Nb-TM-Si-RM (TM: Ti, Hf, RM: W, Mo)-based alloys is in close proximity with the targeted value [132].

4.7 Carbon-based Materials Carbon-matrix composites find enormous application as high-temperature structural materials in space vehicles (e.g., re-entry thermal protection system, rocket nozzles) and aircraft components. Carbon/Carbon (C/C) composites are considered potential candidates for structural applications in hypersonic vehicles, air-breathing engine components, airframe structures, etc. Figure 16 reveals that C/C composites, C/SiC composites, and SiC/SiC CMCs offer an excellent combination of specific-fastrupture-strength at elevated temperatures (>1500 ◦ C) [139]. The major advantages of C/C composites include low density, low thermal expansion coefficient, high specific stiffness, high specific strength, high thermal shock resistance, high thermal conductivity, and superb ability of strength-retention at temperatures higher than 1500 ◦ C. However, the major limitation that poses a challenge for the wide-spread application of C/C composites is its propensity to oxidize at high temperature in presence of air. To mitigate this problem, several research groups are actively involved to enhance the high-temperature oxidation and ablation resistance of C/C composites by various methods. One of the most promising methods is the application of oxidation-resistant SiC [140, 141], ZrC [142], HfC/SiC [143], and mullite [144] coating for producing a physical barrier to resist the inward diffusion of oxygen at high temperature by forming a protective oxide scale [145] at the outer surface. Studies reveal that the incorporation of SiC [146] and ZrC [142, 147] effectively enhances the ablation resistance of C/C composites. On the other hand, the introduction of TiC [148] and B4 C [149] is found to improve the flexural strength of C/C composites. Hu et al. [150] reported that B4 C-B2 O3 -SiO2 -Al2 O3 glass sealant on C/C composite is effective for oxidation inhibition as the incorporation of refractory oxides (SiO2 , Al2 O3 ) retards the volatilization of B2 O3 .

4.8 Ceramics and Composites As discussed in Sect. 3.2, refractory materials serve as critical high-temperature materials in iron and steel processing. Of late, several research groups have contributed significantly in developing advanced refractories for metallurgical sectors [151–154].

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Fig. 11 a TEM image of Ti-45Al-7.5Nb alloy showing ultrafine lamellar structure comprising γ − T i Al and α2 − T i 3 Al, and b comparison of the temperature dependence of specific Young’s modulus of γ -TiAl with other high-temperature structural materials (IMI 834, IN 625, IN 718) (reproduced with permission from [90, 92])

Fig. 12 a Representative microstructure of Ni-based superalloy showing the presence of fcc Ni (matrix) and ordered Ni3 Al precipitates (L12 structure), and b TEM image of Co-Al-W alloy presenting the morphology of Co3 (Al,W) precipitates embedded in solid solution-strengthened Co matrix (reproduced with permission from [43])

Al2 O3 –MgO–C refractories are considered as an alternative to MgO-C refractories for application in the bottom and side walls of steel ladles. Muñoz et al. [155] investigated the thermomechanical characteristics of Al2 O3 –MgO–C refractories and reported the formation of AlN, Al4 C3 , MgAl2 O4 spinel, and Si-containing phases leads to enhanced mechanical strength. Xin et al. [156] developed corundum-spinel refractories with density-gradient structure with excellent mechanical properties and low thermal conductivity. Sako et al. [157] investigated the role of nanoscale MgO and Al2 O3 in Al2 O3 –MgO refractory castable and found that nano Al2 O3 –MgO mixture reduced the expansion of the castable. Luo et al. [158] demonstrated that the thermal shock resistance of porous refractory materials can be studied using

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Fig. 13 Temperature dependence of a yield strength and b 100 h rupture strength of different Ni-based superalloys (data obtained from [41])

Fig. 14 Comparison of variation of 0.2% yield strength with temperature between a Ni-based superalloys (Waspaloy) and polycrystalline Co-Al-W-based superalloys and b Ni-based superalloys and W-containing or W-free Co-based superalloys (reproduced with permission from [111])

Fig. 15 a Creep rate data (in logarithmic scale) of Nb-Si-based high-temperature alloys under a constant load of 170 MPa at 1200 and 1050 ◦ C, and b the same for Nb-Si-based alloys with transition and refractory metal addition under a constant load of 170 MPa at 1200 ◦ C (reproduced with permission from [132])

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Fig. 16 Spectrum of the excellent combination of specific-fast-rupture-strength at elevated temperature offered by C/C composites, C/SiC composites, and SiC/SiC ceramic matrix composites (CMCs) for high-temperature structural applications (reproduced with permission from [139])

the strain-life fatigue approach. Some important areas for future refractory research [159–162] include recycling of refractory, numerical modelling, slag corrosion, and failure analysis. Compared to FM steels and ODS, ceramic matrix composites (CMCs) have emerged as attractive candidates for longevity and safe operation owing to low activation, excellent resistance to oxidation, negligible swelling under irradiation, high fusion point or decomposition temperature, etc. The plasma-facing components (PFCs) in nuclear fusion reactors experience high heat flux (~2–6 MW/m2 ) as well as high neutron flux. Despite several advantages, the use of C/C composites is restricted at high radiation dose (10 dpa or more); hence, SiC/SiC CMCs are explored as structural materials in PFCs in next-generation fusion reactors [163–165]. The use of SiC/SiC-based CMCs as structural materials is envisaged by advanced countries like US, Japan, and EU in their fusion reactor programmes viz., ARIES, DREAM, and TAURO, respectively [166–170]. In addition to fusion reactors, SiC/SiC-based CMCs are also explored for structural applications in nuclear fission reactors [163, 166]. In various areas of gas turbine-modular helium reactor, the use of these CMCs is considered [166]. Owing to excellent performance under irradiation, SiC/SiC-based CMCs are potential candidates for application in fuel-cladding in gas-cooled fast reactor and light water reactor. NASA developed two-piece, toughened unipiece fibre-reinforced oxidationresistant composite (TUFROC) TPS [55, 171]. Surface treatment like RCG-coating coupled with superior design (ROCCI cap, AETB insulating base) brings down the overall thermal conductivity of the composite structure, thereby effectively reducing the heat conducted to the vehicle structure [171, 172]. Aiming at developing new TPS, NASA recently developed flexible TPS [173] and woven TPS [174]. ISRO-VSSC

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developed room temperature curable, cost-effective SSF P70 [175], a low density (0.38 g/cm3 ) thermal protection system, based on silicone polymer, which possesses several significant properties like low thermal conductivity, flexibility, compatibility with metallic as well as composite substrates, high specific heat, excellent ageing behaviour, etc.[175] PC-10 TPS is another ablative thermal protection system, developed by ISRO-VSSC, which exhibits superior moisture resistance, longevity up to 5 years, and can be cured overnight [176]. The maximum service temperature of SSF P70 and PC-10 TPS is 300 and 350 ◦ C, respectively. ISRO also developed silica tile, prepared from amorphous silica fibre, which can withstand up to 1400 ◦ C and offer low thermal conductivity. In collaboration with several other institutes and research laboratories, ISRO uses silica tiles and C/C composites in various areas of its reusable launch vehicle. In order to develop oxidation- and ablation-resistant materials with enhanced hightemperature capability, many research groups in different countries have continued research focussing on ZrB2 , HfB2 , TaC, and HfC-based ultra-high-temperature ceramic (UHTC) composites [177–183]. NASA AEMS has explored ZrB2 –SiC and HfB2 –SiC-based UHTC composites for structural applications in next-generation space vehicles. In recent years, the development of high-entropy carbide- and boridebased UHTC composites has also been reported [184, 185]. Several research groups have achieved a considerable degree of success in designing UHTC composites with superior oxidation resistance, ablation resistance, and superior high-temperature mechanical properties [186–189]. However, the processing of UHTC composites in large dimensions as well as their structure–property correlation in real-life application areas is a major challenge for the successful realization of UHTC technology. Moreover, the availability of ultra-pure UHTC boride and carbides is a major challenge for India since most of these materials are imported from Europe, US, or China. Therefore, the synthesis of UHTC powders in a cost-effective method, their consolidation to large shapes, and property evaluation in simulating environment are important areas of research for developing UHTC technology. Apart from developing UHTC composites, many research groups are exploring the use of C/C composites, either coated or compositionally modified with hightemperature ceramics, as structural materials in critical areas like nose cone [190– 192]. In fine, UHTC-reinforced C/C composites can be synthesized by processes like polymer impregnation and pyrolysis (PIP), melt infiltration (MI), hot pressing (HP), and chemical vapour infiltration (CVI) [193]. Among these, MI-fabricated Zr or Hf-based C/UHTC composites are viable candidates for high-temperature structural applications [193].

5 Future Direction The development of materials and components for high-temperature structural applications has always posed a formidable challenge to designers and engineers. Metallic

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alloys offer ease of processing and fabrication and lend reliability in terms of structural integrity and mechanical behaviour up to a certain temperature. At fairly elevated temperature, metallic components undergo damages caused by accelerated oxidation, creep, and thermal fatigue. In spite of sustained efforts on the development of structural materials for high-temperature applications, the current status is neither adequate nor saturated. In fact, the lack of suitable materials (alloys, composites) poses a serious bottleneck towards pursuing challenging applications in ultra-super critical thermal power plants, long-haul aircraft design, space technology, etc. There is still enormous scope of development to successfully translate emerging technologies into processes and/or products. A synergistic approach combining major engineering branches is, thus, needed to develop new materials for critical application areas.

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Structural Biomaterials for Affordable Health Care Bikramjit Basu, Surya R. Kalidindi, Nandita Keshavan, and Kingshuk Poddar

1 Market Needs and Demands Biomaterials are a class of materials which are used to interface with the components of the living system (proteins, cells, bacteria, tissues). The clinical applicationspecific interactions with living system are embodied in the concept, known as ‘Biocompatability’, which distinguishes biomaterials from other classes of structural/functional materials [1–4]. A few important related terms are defined in Table 1. Figure 1 illustrates the typical anatomical locations in the human body, wherein the clinically validated synthetic biomaterials, implants or biomedical devices can be implanted to replace or restore the functionality of damaged hard or soft tissues. Table 2 outlines classes of different biomaterials for health care. A few priority Disclaimer: The presentation of materials and details in maps used in this chapter does not imply the expression of any opinion whatsoever on the part of the Publisher or Author concerning the legal status of any country, are or territory or of its authorities, or concerning the delimitation of its borders. The depiction and use of boundaries, geographic names and related data shown on maps and included in lists, tables, documents, and databases in this chapter are not warranted to be error free nor do they necessarily imply official endorsement or acceptance by the published or Authors. B. Basu (B) Materials Research Centre, Centre for BioSystems and Engineering,Translational Center On Biomaterials for Orthopaedic and Dental Applications, Indian Institute of Science, Bengaluru, Karnataka 560012, India e-mail: [email protected] S. R. Kalidindi George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, North Avenue, Atlanta, GA 30332, USA N. Keshavan Materials Research Centre, Indian Institute of Science, Bengaluru, Karnataka 560012, India K. Poddar New Materials Business, Tata Steel Limited, Kolkata, West Bengal 700071, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_6

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Table 1 Table of abbreviations Abbreviation

Expansion

3D

Three-dimensional

CAD

Computer-Aided Design

CAGR

Compound Annual Growth Rate

CASPA

Calcium-Sulphate-Phosphate Active composition

CNC

Computer numerical control

CSIR-CGCRI Council of Scientific & Industrial Research-Central Glass and Ceramic Research Institute CMF

Craniomaxillofacial

DBT-COE

Department of Biotechnology sponsored Centre of Excellence

DST

Department of Science and Technology

GLP

Good Laboratory Practice

GMP

Good Manufacturing Practice

GO

Graphene Oxide

HA

Hydroxyapatite

HDPE

High-density polyethylene

ICME

Integrated Computational Materials Engineering

MGI

Materials Genome Initiative

MDSI

Materials Data Science and Informatics

PLD

Pulsed Laser Deposition

PSP

Process-structure–property

R&D

Research and Development

SCTIMST

Sree Chitra Tirunal Institute for Medical Sciences & Technology

THR

Total Hip Replacement

TMJ

Temporomandibular joint

USD

United States Dollar

WHO

World Health Organization

ZTA

Zirconia-toughened alumina

clinical areas in the Indian context which demand the indigenous development of biomaterials include, orthopaedic, craniomaxillofacial, dental, cardiovascular disease, arthritis, osteoporosis, etc. Some of the most recent translational studies from the lead author’s research group in the area of craniomaxillofacial, orthopedic and urological reconstruction applications can be found elsewhere [5–8]. Globally, the medical implant market is estimated to reach $172 billion (|12.2 trillion) by 2023 with a Compound Annual Growth Rate (CAGR) of 7.7% [9]. The Indian orthopaedic and prosthetic device market is estimated to be at $450 million (|31.9 billion) and is experiencing an estimated growth of over 30% per year, with the largest market segments being the joint replacement, spinal implants and trauma [9]. For example, about 70,000 patients with bone disease and fracture need hip

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Fig. 1 Biomaterials for human health care to replace and restore the functionality of the damaged hard tissue (bone), and other structural implants. More than 75% of implants used in Indian hospitals/clinics are imported from Europe or North America. This necessitates the development of high-quality indigenous biomaterials and implants for affordable healthcare in India (adapted from Refs. [2, 3])

Table 2 Classes of different biomaterials for health care Material

Medical applications

Polymers [UHMWPE, PVDF, PDMS, PTFE, etc.]

Hip socket, sutures, blood vessels, lens, ear, nose, tendons and other soft tissues, heart valves, knee implants

Metals [Stainless steel, Ti6Al4V, NiTi, etc.]

Joint replacements, bone plates and screws, dental implants, pacer and suture wires, cardiovascular stents

Ceramics [Al2 O3 , ZrO2 , DLC, etc.]

Femoral head of hip replacement, dental implants, coating of dental and orthopaedic implants

replacement every year in India. High cost and low affordability of devices by poorer people are major concerns, with almost 80–85% of implants being imported. Demand for orthopaedic implants is expected to grow at an estimated rate of more than 25% per annum for the next 5–6 years. The growth is attributed to the growing number of road traffic accidents, sports injuries, orthopaedic impairments (low bone density, osteoporosis and osteoarthritis) and a rising geriatric population at high risk of developing degenerative diseases. Trauma injury, due to accidents as a result of

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poor safety at workplaces and during road accidents, is associated with high morbidity and mortality rates. However, the cost of surgery often remains unaffordable to the majority of patients due to the low prevalence of insurance coverage. Furthermore, the ageing population is often unable to afford medical treatments, related to joint surgeries, due to the high cost of hip and knee implants. The World Health Organization (WHO) estimated that by 2050, 130 million will suffer from osteoarthritis, and 40 million people will be severely disabled by this disease. About 190 million adults and 93 million children experience significant difficulties in normal functioning. In India, approximately 5.3 million people (20% of the disabled population) have a movement-related disability, and this figure is increasing annually since 2011. The number of revision surgeries has increased at about the same rate as that for primary surgeries, and the majority of revisions are due to prosthesis failures. The global market for bone grafts and substitutes is expected to reach $3.4 billion (|240 billion) in 2020 [9]. Humans have different kinesis, which can create different effects on the implants/prostheses inside the body after surgery. Therefore, patientspecific 3D printed implants provide significant benefits. The global dental implants and prostheses market is estimated to grow at a CAGR of 6.1% during 2018–2024, reaching approximately $12 billion (|850 billion) in 2025. Total edentulism in the general population varies from 14 to 16%, mostly in the 60 + age group, providing a growing opportunity for market players to target the huge population suffering from tooth loss [9]. The product segments of craniomaxillofacial (CMF) devices (restoring or replacing areas of the mouth, jaws, face, skull and associated structures) encompass temporomandibular joint (TMJ) replacement, CMF distraction, cranial flap fixation, CMF plate and screw fixation, bone graft substitutes and thoracic fixation. There is a high unmet need for patient-specific prostheses in neurosurgical procedures. It is clear that the availability of affordable implants is expected to enable people to be able to access better health care. There is a significant demand to indigenously develop cranial prostheses to reconstruct the cranial vaults after surgery. The global market size for CMF devices and implants was estimated to be at $1.4 billion (|99 billion) in 2017, and is predicted to grow at a CAGR of 8.6% over the period 2018–2024, reaching approximately $3 billion (|212 billion) by 2025 [9]. In the above perspective, we need to take note of the fact that the ageing population, and particularly the financially challenged population in developing nations like India, tend to be unable to afford medical treatments due to the high cost of imported medical devices. Also, the majority of currently used implants are available in standard shapes and sizes, and are not made specifically for the Indian population. A number of multinational corporates are actively marketing their implants and biomedical devices globally. Some of the major players are listed in Table 3, together with their significant products.

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Table 3 Major global players in manufacturing and commercialising biomaterial implants related to Orthopaedic, dental and trauma implants only. This list however is not an exhaustive one Company

Significant products

Materialise

Variety of patient-specific titanium implants

Renishaw

3D printed dental frameworks and mandibular implants using titanium alloys

Anatomics

Metal and HDPE cranial, facial and chest implants

RMS partnering with 3D systems

Materials and method for 3D printing of metal implants

OssDesign

3D printed cranial implant technology using titanium alloys

4WEB Medical

3D printed titanium implants for spine, foot and ankle replacements

Medicrea

Large portfolio of 3D printed titanium implants

Additive Orthopaedics

Hammertoes replacement implants

K2M Group Holdings Inc

A variety of titanium-based implants

DentCare

A variety of dental prostheses

Straumann AG

Dental implants, instruments, biomaterials, CAD/CAM prosthetics, digital equipment, software, and clear aligners for replacement, restorative, orthodontic and preventative dentistry

Dentsply Sirona

Dental equipment and consumables

Henry Schein

Dental and medical devices

Danaher Corporation

Dental solutions

Orchid Orthopedics

Orthopaedic medical devices

Stryker

Products and services in orthopaedics, neurotechnology, spine and other medical areas

Zimmer Biomet

Musculoskeletal health care

DePuy Synthes—subsidiary of Johnson and Johnson

Joint reconstruction, trauma, spine, sports medicine, craniomaxillofacial, power tools and biomaterials

Smith and Nephew

Wound management products, arthroscopy products, trauma and clinical therapy products, and orthopaedic reconstruction products

Meril Healthcare

Vascular intervention devices, orthopaedic supplements, in vitro diagnostics, endo-surgery and ENT products

Inor Orthopaedics

Products for the joints, trauma and spine sectors

Biorad Medisys

Implants used in arthroplasty; medical devices used in urology, gastroenterology, radiology and minimally invasive surgery

TTK

Orthopaedic implants (continued)

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Table 3 (continued) Company

Significant products

Sharma Orthopedics

Orthopaedic implants and instruments

SH Pitkar

Orthopaedic implants and instruments

Matrix Meditec

Trauma, spine, hip replacement products and instruments

Medtronic

Orthopaedic products

NuVasive

Medical devices and procedures for minimally invasive spine surgery

Globus Medical

Spine and trauma products

Maxx Medical

Knee replacement products

Orthotech India Pvt. Ltd.

Orthopaedic joint implants (hip, shoulder, wrist)

Arka Medical Devices Pvt. Ltd.

Dental implants, maxillofacial implants

Jajal Medical

Orthopaedic (implants, guides and trauma plates), Neurosurgical (cranial plates), Oral maxillofacial (templates and guides) implants

2 Current Status of Development in India In the last few decades, significant progress in the field of biomaterials and implants in India has been attained (Fig. 2). For the benefit of readers, a list of terms of clinical relevance to biomaterials/implants is summarised in Table 4. The field has evolved and grown rapidly in India over the years and has emerged as a common platform for engineers, biologists, chemists and medical doctors to work collaboratively on next generation biomaterials and implants. Innovation in the field has progressed from the development of inert biomaterial implants to the development of more dynamic, stimuli-responsive biomaterials. The biomedical implant innovation cycle is shown in Fig. 3. One can perceive long product development cycles for products to reach the market. One of the major time-limiting steps in this process is the regulatory approval and prototype-testing, particularly clinical trials. Although most research activities are focused on laboratory-scale development, the researchers from a few national labs and academic institutes have tried their best to take laboratory-scale research to product-prototype development, in order to reach the patient’s bedside. We shall now briefly mention the major Indian attempts in the biomedical landscape.

2.1 National Laboratories There are several national institutions pursuing research in this field, including National Institute of Technology, Rourkela; BMS College of Engineering, Bengaluru; Jadavpur University, Jadavpur; National Institute of Technology, Durgapur; Indian

Fig. 2 Landscape of Biomaterials and implants in India: Major research group in academia, national labs and institutes [9]

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Fig. 3 Product development cycle of biomaterials or implants, showing the concept of ‘BedsideBench-Bedside’ translation [9]

Table 4 Selected definitions of clinical relevance to biomaterials and implants [1] Term

Definition

Bactericidal

Substance that kills bacteria, or the effect of killing bacteria

Biocompatibility

The ability of a material to perform with an appropriate host response in a specific application

Biomaterial

Material designed to take a form which can direct, through interactions with living systems, the course of any therapeutic or diagnostic procedure

Craniectomy

Surgery done to remove a part of the skull in order to relieve pressure in that area

Cytocompatibility Compatibility of a biomaterial with biological cells Genotoxicity

Toxicity to the genome

Implant

A medical device made from one or more biomaterials that is intentionally placed, either totally or partially, within the body

Osteoconductive

Capable of promoting differentiation of progenitor cells down an osteoblastic lineage

Osseointegration

The capability of substrate-adherent osteoblasts to produce bone

Scaffold

3D porous structure which serves as a substrate and guides for tissue repair and regeneration

Institute of Engineering Science and Technology (IIEST), Shibpur; Punjab Engineering College; Andhra University College of Engineering; Indian Institute of Technology, Kanpur; Indian Institute of Science, Bengaluru; Council of Scientific and Industrial Research-Central Glass and Ceramic Research Institute (CSIRCGCRI), Kolkata; Sree Chitra Tirunal Institute for Medical Sciences and Technology (SCTIMST), Thiruvananthapuram; Institute for Stem Cell Biology and Regenerative

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Medicine (InStem), Bengaluru; and Central Institute of Petrochemicals Engineering and Technology (CIPET), Chennai. The scientists of CSIR-CGCRI developed technologies for Al2 O3 -based ceramic femoral head and matching articulating liner for ceramic-on-ceramic total hip joint replacement. Al2 O3 -based ceramic femoral heads of different sizes are prepared by CSIR-CGCRI for ceramic-on-polyethylene (PE) based total hip joint replacement (THR). The clinical efficacy of these femoral head and cups have been established in monocentric clinical trials. For the purpose of implant testing, CSIR-CGCRI has hip joint simulator and knee joint simulator facilities. IIT Guwahati researchers recently designed and developed hip joint wear simulator and orbital hearing machine, for the first time in India. Multi-ion doped HA-based granules with antimicrobial properties are being developed for accelerated tissue integration. Lightweight, highly porous orbital implants made using bioactive hydroxyapatite of different sizes to suit different patients are developed at CSIR-CGCRI with their clinical performance being validated. Significant research on injectable biodegradable bone cement has been conducted at national labs in India. The technology, developed at CSIR-CGCRI, constitutes the composition and preparation of a self-setting, injectable bone cement with and without a drug. Clinical trials have been completed, and to enable post-implantation identification and evaluation, modification of the cement with radiopaque particles is in progress. Bioactive bone cement, a self-setting formulation containing osteoconductive inorganic phases, named Calcium-Sulphate-Phosphate Active Composition (CASPA), has been developed and was evaluated by researchers at SCTIMST, a DST-funded institute of national importance. Pre-clinical studies were completed and human clinical trials are ongoing.

2.2 Translational Centre of Excellence on Biomaterials One of the leading examples of the large translational research programs in Indian landscape is the DBT-funded translational Centre of Excellence on orthopaedic and dental biomaterials, referred to further as the DBT COE. This centre has brought together 15 investigators and 37 young researchers from multiple disciplines, including Bioceramics, Biopolymers, Biomechanics, Mechanical Engineering, Dentistry, Orthopaedic surgery and Histopathology. The key details and impact of DBT COE is illustrated in Fig. 4. The researchers have demonstrated modulation of protein adsorption and stem cell/osteoblasts/muscle cell proliferation on 3% PE-g-GO-reinforced HDPE, compared to that on unmodified 3% GO-reinforced HDPE composite together with better elastic modulus and yield strength. Also, HDPE-UHMWPE-modified GO nanocomposites enhance the mechanical properties with uncompromised cytocompatibility. Further, the team has fabricated acetabular liner prototypes of different sizes using a compression moulding approach. DBT-COE researchers also established a novel manufacturing protocol to fabricate defect-free femoral heads. They employed a statistical tool to develop a rapid

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Fig. 4 Key details and impact of the Department of Biotechnology, Government of India-funded translational center for excellence on biomaterials for orthopedic and dental applicants [9]

and robust process-optimisation technique to develop highly dense oxide bioceramics with finer microstructure, optimum mechanical response and excellent cytocompatibility. Using an Integrated Computational Materials Engineering (ICME) approach for the optimisation of sintering parameters, the researchers of NIT Rourkela in collaboration with IISc, Bangalore prudently developed process protocols for femoral head prototypes of zirconia-toughened alumina (ZTA) with reliable mechanical properties. In collaboration with prosthodontist at Ramaiah University of Applied Sciences, Bangalore, the lead author’s research group, under the framework of DBT-COE programme, designed and developed a new generation of dental implants with hybrid threads and anti-rotational features. The conventionally manufactured implant prototypes exhibited clinically acceptable insertion torques in cadaver and porcine bone as well as better bone engagement during osseointegration study using rabbit condyle model at SCTIMST, Trivandrum. The pre-clinical testing and biomechanical simulation established better properties than commercial dental implants, Currently, high volume manufacturing of implant in a GMP-compliant facility is under progress and the clinical studies at three hospitals i.e. King George’s Medical University, Lucknow, Datta Meghe Institute of Medical Sciences, Wardha and Ramaiah University of Applied Sciences, Bangalore are going to commence soon. The regulatory approval process is currently underway. A team of researchers at Indian Institute of Science, Bengaluru, together with a group of neurosurgeons, based in Ramaiah hospital, Bangalore has developed a technology to fabricate low-cost, fully functional patient-specific cranial implants. 3D cranial models serving as templates for the fabrication of patient-specific acrylic implants for cranial defects were printed using 3D inkjet powder printing, with

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the help of a patented binder. Multicentric clinical trials at different hospitals have established patient safety and clinical efficacy of the indigenously developed cranial prosthesis in human subjects with craniectomy defects. The post-operative analysis revealed the restoration of clinically acceptable Cranial Symmetry Index and Glasgow Outcome Score in the treated patients.

2.3 Kalam Institute of Health Technology, MediValley and AMTZ Andhra Pradesh Med Tech Zone Biomaterials testing is a critical step in the process of transforming an innovative design into a reliable and marketable product. To evaluate the safety and efficacy of biomaterial products and to meet the requirements for obtaining marketing authorisation, thorough laboratory testing is required in order to understand aspects related to product safety, such as their biocompatibility, or performance criteria, such as mechanical properties. The BIOME facility setup by AMTZ is operated and maintained by TUV Rheinland India, which allows the manufacturers to test and validate their products, thereby enhancing product value in the market. The state-ofthe-art laboratory, which is primarily intended for the medical device industry for physico-chemical evaluation as well as biological evaluation of samples, can also serve incubators and start-ups. BIOME provides facilities of sophisticated analytical instruments to industries, and R&D laboratories, scientists and other users from academic institutes to enable them to carry out measurements for testing, and R&D work as per ISO 10993 guidelines and relevant ASTM standards. Kalam Institute of Health Technology (KIHT), a society funded by the Department of Biotechnology, Government of India, functions primarily in the area of translatable research in the domain of medical technologies. KIHT is situated at the Andhra Pradesh Med Tech Zone, which represents India’s only medical devices industrial zone.

3 Future Perspective Translation of laboratory-scale inventions to advanced medical technologies and biomaterials is crucial in the development of the next generation of biomedical devices. By 2035, one can expect that several principal focus areas, including regenerative medicine, nano-medicine, stem cell therapeutics, immunomodulation and miniaturised medical devices, will be extensively explored. Alongside these areas, it is essential to employ significant efforts in devising innovative and effective strategies in conducting clinical trials relevant to the Indian population, thus encouraging quality clinical research in our country. Worldwide, the number of clinical trials is

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increasing by around 10–12%/year. Conducting clinical trials in developing countries, however, often presents significant ethical, organisational, cultural and infrastructural challenges to researchers, biomedical device companies, sponsors and regulatory bodies. Patient recruitment is a key factor which can be done through focused interviews with patients and caregivers to provide the best chance of maximising data collection from subject populations. With respect to translational activities, the design cycles in new biomaterials or biomedical device development, in the order of 5–15 years, are considerably longer than those for the engineered components used in various non-biomedical technologies (see Fig. 3). Other than time, high cost is another factor often associated with the successful development and deployment of new materials into high-performance commercial products. Some of the reasons for the higher time and cost involved are (a) heavy reliance on experimental data, (b) disconnect between experiments and simulations, (c) lack of widely accessible data, (d) lack of databases and infrastructure to support the application of a universal systems approach and (e) lack of an appropriate ecosystem for sustaining cross-disciplinary collaborations. The emerging discipline of Materials Data Science and Informatics (MDSI) promises to address these key technology gaps, as the novel concepts and toolsets offered by MDSI will substantially benefit the materials innovation enterprise. Recent and ongoing initiatives such as Integrated Computational Materials Engineering (ICME) [10–12] and the U.S. Materials Genome Initiative (MGI) [13–19] aim to reduce the cost and time involved in bringing new materials to market. These initiatives have already set the stage for major transformations of the future materials innovation workflows. The focus of these efforts is largely on structural and functional materials required to further aerospace, automobile and energy technologies. The initiatives aim to develop and demonstrate novel frameworks and protocols for automated data ingestion, structured data storage, high-throughput exploration of experiments and models, and integrated data analytics. Furthermore, there are substantial cultural barriers to data sharing, which are being addressed by developing novel ecollaboration tools that encourage contribution through increased productivity for all team members. Ultimately, the confluence of an efficient technical infrastructure of stakeholders is expected to create a vibrant data-driven cyber-ecosystem. This would accelerate materials innovation and enable the realisation of a revolutionary impact of big data on the materials and manufacturing sectors. The main components of this materials innovation cyber-ecosystem are (i) Highthroughput strategies for measurement, capable of undertaking rapid and highly targeted explorations of PSP linkages of high value to manufacturing processes employed by industry. (ii) Standards and systems for the automated ingestion of data and metadata (important information about the data that enhance relevance and retrievability in both experimental and modelling studies). (iii) Data storage, management and curation systems capable of handling the big data that will be created in cross-disciplinary activities by diverse stakeholders. (iv) Data analytics frameworks capable of fusing information from different sources and extracting consistent highvalue information (i.e., knowledge). (v) Industry outreach and consortia capable of translating the advances made into successful commercial products. (vi) Education

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and training programs that produce a new workforce of materials engineers with skills derived from both data and materials sciences. Against the above backdrop, it is appropriate now to recognise the opportunities presented by these initiatives to biomaterials innovation. There is a great overlap in the currently employed protocols in the innovation of biomaterials and structural materials, and the potentially major markets that are likely to open up in India for bioimplants; hence, it is now appropriate to establish national policies and investments that will result in strategic and win–win public–private partnerships. Indeed, many short- and long-term opportunities are provided by the emergent tools in data science and informatics for addressing several of the current challenges in the biomaterials/bioengineering field. In particular, these new tools can help address the current major gaps in our fundamental understanding of how the microstructure and material composition influence cell functionality, bone remodelling, genotoxicity and osseointegration. This has been significantly discussed in a recent review [13]. It is expected that future research at the intersection of biomaterials, bioimplants, materials science, manufacturing, data sciences and informatics holds tremendous promise in substantially reducing the cost and effort involved in developing new and improved materials. The emerging toolsets in MDSI offer several new opportunities for addressing the above challenges through novel cyber-infrastructure elements; these can be specifically designed to address the needs of the biomaterials community.

4 National Roadmap The authors suggest a significant national investment aimed at realising the following objectives to build a strong translational research ecosystem in the field of biomaterials in India. Extensive details of most of the following aspects can be found in a monograph published by Springer [9]. i.

ii.

Immediate term goals (a) Intense interaction and collaboration for identifying and implementing faster GLP-compliant biocompatibility testing, certification and commercialisation protocols [13]. (b) Adapt and implement ‘Biomaterialomics’ approach in collaboration with Data Scientists to predict clinical performance of the next generation biomaterials implants, using digital twins [13]. Short-term goals: a. b.

Implement a national regulatory framework to facilitate the acceleration of regulatory approval processes. Involvement of multinational companies, like TATA Steel and Micro, Small and Medium Enterprises (MSMEs) for producing biomaterials and biomedical implants in Good Manufacturing Practice-regulated (GMP) facilities.

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Medium-term goals: a. b. c.

d. e. f. g. iv.

Strengthen basic research for building an innovation knowledge base on the next generation of biomaterials. Build up clinical, treatment-driven translational research within the context of human illnesses. Fully integrated manufacturing life cycles that start with raw materials and end with biomedical devices, while leveraging both conventional and advanced manufacturing capabilities. Support industry capabilities and collaborations, including growing and sustaining incubators and start-ups. Revamp the medical education system and clinical research ecosystem, to develop a trained and collaborative clinician ecosystem. Introduce, improve and implement national policies and roadmaps to allow the field of biomaterials to benefit society. Accelerate ethical approvals for pre-clinical/clinical trials using computerised workflows.

Long-term goal: a.

Developing new markets and GMP compliant manufacturing facilities for producing large volumes high-quality implants to compete with imported devices.

It is recommended that materials engineers, clinicians and industry professionals develop a scientifically, ethically and socially mindful platform, to foster advances in materials science and medicine within clearly defined boundaries. Acknowledgements BB and NK are grateful for the support of the Department of Biotechnology, Government of India, and the Translational Centre of Excellence for Biomaterials on Orthopedic and Dental Applications, the Bioengineering and Biodesign Initiative at Indian Institute of Science, and the Science and Engineering Research Board’s Core Research Grant, Government of India. SRK acknowledges VAJRA fellowship of SERB, Government of India.

References 1. B. Basu, Biomaterials Science and Tissue Engineering: Principles and Methods. Cambridge University Press, Cambridge (2017) 2. B. Basu, Biomaterials for Musculoskeletal Regeneration: Concepts. Springer Nature (2017) 3. B. Basu, S. Ghosh, Biomaterials for Musculoskeletal regeneration: Applications. Springer Nature (2017) 4. B. Basu, N. Keshavan, B. Bhagawati, D. Bhattacharjee, Biomedical Implants and Materials: Innovation, Opportunities and Challenges. Think Pot Advertising Pvt. Ltd, Kolkata (2019) 5. B. Basu, N. Bhaskar, S. Barui, V. Sharma, S. Das, N. Govindarajan, P. Hegde, P.J. Perikal, M.A. Shivakumar, K. Khanapure, A.T. Jagannatha, Evaluation of implant properties, safety profile and clinical efficacy of patient-specific acrylic prosthesis in cranioplasty using 3D binderjet printed cranium model: A pilot study. J. Clinic. Neurosci. 85, 132–142 (2021)

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6. S. Barui, A.K. Panda, S. Nasakar, R. Kuppuraj, S. Basu, B. Basu, 3D inkjet printing of biomaterials with strength reliability and cytocompatibility: Quantitative process strategy for Ti-6Al-4V. Biomaterials 213, 119212 (2019) 7. S. Sharma, A. Mandhani, S. Bose, B. Basu, Dynamically crosslinked polydimethylsiloxanebased polyurethanes with contact-killing antimicrobial properties as implantable alloplasts for urological reconstruction. Acta Biomaterialia 129, 122–137 (2021) 8. V. Sharma, S. Chowdhury, N. Keshavan, B. Basu, Six decades of U HMWPE in reconstructive surgery: A biomaterial’s perspective on developments and emerging opportunities. Int. Mater. Rev. (in Press, 2022) 9. B. Basu, Biomaterials Science and Biomedical Implants: Status, Challenges and Recommendations. Springer-Indian National Science Academy (2020) 10. D. Sarkar, B.S. Reddy, B. Basu, Implementing statistical modelling approach towards development of ultrafine grained bioceramics: Case of ZrO2 –toughened Al2 O3 . J. Am. Ceramic Soc. 101(3), 1333–1343 (2018) 11. G.J. Schmitz, U. Prahl, ICMEg–the integrated computational materials engineering expert group–a new European coordination action. Integr. Mater. Manuf. Innovat. 3(1), 2 (2014) 12. T.M. Pollock et al., Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security (The National Acamedies Press, Washington DC, 2008) 13. B. Basu, N.H. Gowtham, Y. Xiao, S.R. Kalidindi, K.W. Leong, Biomaterialomics: Data Science-driven Pathways to develop fourth-generation Biomaterials and Implants. Acta Biomaterialia (in Press, 2022) 14. C. Kim et al., Polymer genome: a data-powered polymer informatics platform for property predictions. J. Phys. Chem. C 122(31), 17575–17585 (2018) 15. D.L. McDowell, S.R. Kalidindi, The materials innovation ecosystem: a key enabler for the materials genome initiative. MRS Bull. 41(04), 326–337 (2016) 16. M. Drosback, Materials genome initiative: advances and initiatives. JOM 66(3) (2014) 17. G.B. Olson, C.J. Kuehmann, Materials genomics: from CALPHAD to flight. Scripta Mater. 70, 25–30 (2014) 18. C.M. Breneman et al., Stalking the materials genome: a data-driven approach to the virtual design of nanostructured polymers. Adv. Func. Mater. 23(46), 5746–5752 (2013) 19. A. Jain et al., Commentary: the materials project: a materials genome approach to accelerating materials innovation. APL Mater. 1(1), 011002 (2013)

FRP Composites: A Prospective Structural Material for the Indian Landscape Rajesh Kumar Prusty and Bankim Chandra Ray

1 Introduction to Composite Materials A composite material comprises two or more materials of different properties which, when combined, forms distinct layers without blending into each other, giving properties different from the properties of its constituent materials. Composites today have started being widely used in aerospace and aviation, industry, as well as in medical technology. Wood is a natural composite in which lignin holds the cellulose fibres. The constituent materials can be of two main categories, namely matrix and reinforcement. For synthetic composites, the matrices used may be organic like ester and epoxies, or inorganic like concrete, metals, and ceramics. Similarly, the reinforcements used are of different types. The composite materials show typically anisotropic properties. This anisotropy gives high but directional mechanical properties which feature in the design. The advantage of composite materials when compared to conventional materials is that the former has a high strength-to-weight ratio, and can be designed for specific purposes by choosing a suitable combination of matrix and reinforcement materials. High-strength composite materials can be designed to be stronger than steels.

1.1 Fundamentals of Composite Materials Ashby’s diagram (Fig. 1) gives a basic idea regarding the position of composite materials among other materials in terms of density and strength.

R. K. Prusty · B. C. Ray (B) Metallurgical and Materials Engineering, FRP Composite Laboratory, National Institute of Technology, Rourkela 769008, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_7

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Fig. 1 Ashby’s diagram [1]

The type and quantity of the reinforcement are responsible for determining the final properties of the composite. It is the reinforcement which provides strength and stiffness; it may be a fibre or a particulate. The matrix is crucial for transferring the load to fibres through shear loading. It also maintains proper orientation and spacing of fibres, thereby protecting the composite from abrasion. The key feature characterizing the design and manufacture of high-performance composites with specific functional requirements is the good changeability potential of composites, i.e., the properties of the composite can be tailored based on the application requirements. For example, the physical property tensors of a particular material can be customized over a wide range by varying its structural parameters like composition, symmetry, connectivity, and periodicity.

1.2 Classification of Composite Materials Figure 2 shows the broad classification of composite materials. One may develop a composite taking various combinations of reinforcements and matrices following a

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Fig. 2 Classification of composite materials

suitable technique of fabrication. Particulate composites generally have less reinforcement, have less stiffness, and are generally weaker as compared to fibrereinforced composites. The particulates may be spherical, like platelets, or of any other uniform or non-uniform geometry. Continuous-fibre composites have large aspect ratios and preferred orientation, in contrast to discontinuous-fibre composites. Thermosetting and thermoplastic polymers are the two types of polymer matrices used for polymeric composites. Commonly used reinforced plastics have polymer matrices reinforced with low stiffness glass fibres. On the other hand, advanced composites consist of fibre and matrix combinations which yield good stiffness and superior strength. Metal matrix composites offer the advantage of high operating temperatures (~500 °C/773 K) with a major disadvantage of having a higher specific gravity. In the case of fibre-reinforced polymer (FRP) composites, rigidity can be calculated; they fatigue slowly, damp vibrations effectively, offer high corrosion and erosion resistance, and have good X-ray transparency as well as low thermal expansion. They are thus widely used in varied applications and have become a major area for research and development. They have emerged as a significant class of structural materials, and are either being used or being considered for use as an alternative for metals in weight-critical components in industries like aerospace, automotive, and others. Nevertheless like any other material, there also exist some associated disadvantages/limitations of FRP composites. Laminated FRP composites usually exhibit poor out-of-plane mechanical performance. Poor interfacial bond strength in some of the

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FRP composites may lead to gross delamination as well. Availability and cost of raw materials may be an issue at some time. For most of the advanced FRP composites being made up of thermosetting polymers, recyclability is a crucial environmental concern. Further, polymers being sensitive to many environments like UV, ozone, various radiations, humidity, and so on, the durability analysis of such composites is a must under several in-service environments.

1.3 Fibre-Reinforced Polymer Composites 1.3.1

General Characteristics

We can get a large combination of elastic modulus and strength from an FRP which are very much similar to or even better than many conventional metallic materials (Table 1). The strength and modulus of unidirectional composites depicted in the table are taken in the direction of fibres. It is also seen that many of the FRP composites have excellent fatigue strength and can tolerate damage due to fatigue. In terms of design, the FRP composite structures are complex than the metal structure. But the anisotropy of the FRP composites allows tailoring the properties according to design requirements. This is an advantage of the FRP composites that can be effectively utilized in a number of ways reinforcing a structure selectively in the direction where stress is more and where the stiffness is needed to increase. Curved panels with no secondary forming operation or negligible thermal expansion coefficient structures can be fabricated with this. Another unique material is a sandwich structure in which aluminium honeycomb or plastic or metal foam is enveloped between two FRP laminates, which provides it with another degree of design flexibility that cannot be found even in metals. The stiff skin material and a lightweight core can give a very high rigidity and toughness without any increase in weight. One of the remarkable characteristics of FRP composites is high internal damping which makes it a very useful material to be used in sporting goods and automotive applications. However, this requires proper selection of the reinforcement and matrix. FRP in automotive applications can provide great comfort to passengers. This will result in better vibration absorption in the material, reduce noise to the structures nearby components, and improve the safety features. Another advantage of FRP composites is their non-corroding nature. Still, they are prone to environmental damages caused by moisture- or chemical absorption which can lead to change in dimension or even internal stress in the material. In addition to this, one-step production of the acoustic panel, aesthetic panels, and easy production of complicated design products are some of the attractive key features for the wide range acceptability of these FRP composites for various architectural designs.

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Table 1 Tensile properties of some metallic and structural composites [2] Materials

Density g/cm3

Modulus GPa

SAE 1010 steel (cold-worked)

7.87

207

365

303

2.68

AISI 4340 steel (quenched and tempered)

7.87

207

1722

1515

2.68

22.3

6061-T6 aluminium alloy

2.70

68.9

310

275

2.60

11.7

7178-T6 aluminium alloy

2.70

68.9

606

537

2.60

22.9

Ti-6Al-4 V titanium alloy (aged)

4.43

110

1171

1068

2.53

26.9

17–7 PH stainless steel (aged)

7.87

196

1619

1515

2.54

21.0

INCO 718 nickel alloy (aged)

8.2

207

1399

1247

2.57

17.4

High-strength 1.55 carbon fibre–epoxy matrix (unidirectional)

137.8

1550

−

9.06

101.9

High-modulus 1.63 carbon fibre–epoxy matrix (unidirectional)

215

1240

−

13.44

77.5

E-glass 1.85 fibre–epoxy matrix (unidirectional)

39.3

965

−

2.16

53.2

Kevlar 49 1.38 fibre–epoxy matrix (unidirectional)

75.8

1378

−

5.60

101.8

Boron fibre–6061 Al alloy matrix (annealed)

2.35

220

1109

−

9.54

48.1

carbon 1.55 fibre–epoxy matrix (quasi-isotropic)

45.5

579

−

2.99

38

Sheet-moulding compound (SMC) Composite (isotropic)

15.8

164

−

0.86

1.87

Tensile strength MPa

Yield strength MPa

Specific modulus, 106 m

Specific strength, 103 m 4.72

8.9

154

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Manufacturing Processes

The hand lay-up technique is a simple and low-cost moulding method where a resin coat is first applied to the mould, and then manually fibre reinforcement is placed on it. Rollers are used to cohere the laminate and remove any entrapped air. Subsequently, more fibre layers are added to make the laminate of the desired thickness. In automated spray lay-up, using a hand-held gun, fibre is chopped in and fed into a spray of catalysed resin. But the major disadvantage is that the laminates thus produced are excessively heavy and resin-rich. The incorporation of only short fibres severely restricts the mechanical properties of the prepared laminate. The applications include simple enclosures, lightly loaded structural panels, e.g., caravan bodies and bathtubs, shower trays, and some small dinghies. In the process of resin infusion, the resin is filled into the voids of an evacuated stack of porous material. On solidification, the resin binds all the materials into a stiff composite. A vital part of this process is the evacuation of air from the porous material before adding the resin. The bulk moulding process incorporates a bulk moulding compound which is a ready-to-mould, glass-fibre-reinforced thermoset polymer material. It is manufactured at room temperature by mixing strands of chopped glass fibres, with initiator styrene and filler in a thermoset resin. The mixture is stored at low temperatures so that curing is slowed down. Sheet moulding can be performed by compression or injection; the compounds are a combination of long chopped glass strands, thermosetting resin, and mineral fillers. The pultrusion process produces composites with high Fibre Volume Fraction (FVF) and high strength-to-weight ratio. The reinforcement is pulled into the infeed area and then impregnated in the matrix with resin. It is then cured and allowed to cool; thereafter, it is clamped and pulled by the reciprocating puller units. In the filament winding process, the fibre is continuously passed through a resin bath. Winding of this fibre is subsequently done on a rotating mandrel (which serves as a mould) in some pattern. Autoclave-based manufacturing is another advanced technique where curing of the polymer is generally carried out in an autoclave with several curing cycles comprising various combinations of heat, pressure, and inert gas.

1.4 Applications of FRP Composites There is so much variation in the commercial and industrial applications of fibrereinforced polymer composites that it is almost impossible to list them all. Some of the major structural applications are discussed here.

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Table 2 Early application of FRP in military aircraft [2] Aircraft

Components

F-14 (1969)

Skin on the horizontal stabilizer box

Material

Metal component %

Boron fibre–epoxy

19

Carbon fibre–epoxy

−

Boron fibre–epoxy

25

F-11

Under the wing fairings

F-15 (1975)

Fin, rudder, and stabilizer skins

F-16 (1977)

Skins on vertical fin box, fin leading edge

Carbon fibre–epoxy

23

F/A-18 (1978)

Wing skins, horizontal and vertical tail boxes, wing and tail control surfaces, etc

Carbon fibre–epoxy

35

AV-8B (1982)

Wing skin and substructures, forward fuselage; horizontal stabilizer; flaps: ailerons

Carbon fibre–epoxy

25

1.4.1

Aircraft and Military Applications

Major structural applications for FRP composites are found in military and commercial aircraft. FRP composites dominate this field as the aircraft demand weight reduction critical for higher speeds and increased payloads. In 1969, FRPs witnessed major growth in the aircraft industry because of the production application of boron fibrereinforced epoxy skins for F-14 horizontal stabilizers. In the 1970s, carbon fibres were introduced thereby making carbon fibre-reinforced epoxy the primary material in many wings, fuselage, and empennage components. Table 2 shows the early applications of FRP in military aircraft. Introduced in 1988, Airbus A320 was the first commercial aircraft to have a tail completely made up of composites which included components like the horizontal stabilizer, vertical stabilizer as well as tail cone. In 2007, Airbus A380 (Fig. 3) was introduced in which composites comprised 25% of its weight. Figure 4a shows the 787 Dreamliner which had its first flight in 2009. The 787, intended to replace the 767, was designed to be 20% more fuel-efficient. The airframe of the 787 was made of roughly 50% composites, 20% aluminium, 15% titanium, and the rest being a mix of steel and plastics. As of March 2017, the 787 had orders for 1,211 aircraft worth nearly $400 billion from 64 customers. Figure 4b shows the B2 stealth aircraft on which CFRP coating contributes to its stealth characteristics.

1.4.2

Naval and Marine Applications

Corrosion is the major problem faced with the use of steel or aluminium alloys, while wood suffers from environmental degradation. So, FRP composite applications were initially directed to overcome these drawbacks. Additionally, the topside weight of the ships could be reduced with the use of composites. Ship radomes as

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Fig. 3 Use of fibre-reinforced polymer composites in airbus A380 [3]

Fig. 4 Extensive use of FRP composites in a Boeing 787 dreamliner and b B2 stealth aircraft USAF [4, 5]

well as the sonar domes of submarines benefited from the high acoustic transparency of composites. FRP patrol boat is increasingly becoming popular mainly due to lightweight composites having excellent corrosion resistance, which reduce maintenance costs as well as can result in higher speed and fuel economy. It is estimated that the FRP composite patrol boats are generally approximately 10% lighter than an aluminium boat and over 35% lighter than a steel boat of the same size. The high cost of Carbon fibre composites limits its usage in naval vessels. Propulsion shafts made from composites are predicted to be 18–25% lighter than steel shafts of the same size along with a reduction in life cycle cost by a minimum of 25% because of fewer issues related to corrosion and fatigue. Figure 5a shows a Composite houseboat, developed under the aegis of a project under the Advanced Composites Programme of TIFAC for improved aesthetics, boat stability, comfort level, and maintainability for tourism. In partnership with

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Fig. 5 Naval applications of FRP composites [6, 7]

M/s. Samudra Shipyard Pvt. Ltd., Aroor, the project, was launched near Cochin. NGN Composites of Chennai has assisted in the mechanical design and fabrication of hull, deck, and superstructure. Figure 5b shows the Visby-class corvette of the Royal Swedish Navy, the largest composite ship in the world.

1.4.3

Civil Structures

Due to the high strength-to-weight and stiffness-to-weight ratios, as well as the light weight and corrosion resistance, FRP composites have several potential applications in civil engineering. The revamping of constructed facilities and infrastructure such as buildings, bridges, and pipelines is of most importance. Due to the changeable performance characteristics, ease of application, and low life cycle costs, the use of FRP composites has increased in the rehabilitation of concrete structures and the development of new lightweight structural concepts. Figure 6a shows the huge One Ocean Thematic Pavilion, South Korea, made up of FRP, and Fig. 6b shows the interior of the Bing Concert Hall located in Stanford, CA, USA, completed in 2011. Figure 6c shows West Natick Mini High platforms for accessibility. All the panels for platforms were delivered on one truck. The largest panel measuring around 8 m × 2 m weighed only less than 1500 kg.

1.4.4

Automotive Applications

In the automotive industry, FRP composites on the basis of applications can be classified into three groups, viz. body components, chassis components, and engine components. Exterior body components, such as the hood or door panels, require high stiffness and damage tolerance (dent resistance) as well as a ‘Class A’ surface finish for appearance. E-glass fibre-reinforced sheet moulding compound (SMC) composites are a suitable composite material for this application. The tooling cost for compression moulding SMC parts can be 40%–60% lower than that for stamping steel parts. An example of part integration can be found in radiator supports in which SMC is used as a substitute for low carbon steel. With as much as 80% weight

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Fig. 6 Infrastructural use of FRP composites: a One ocean thematic pavilion, South Korea [8], b Interior of the bing concert hall stanford, CA, USA [9], and c West Natick mini-high platforms [10]

reduction, unileaf E-glass fibre-reinforced epoxy springs have been used to replace multi-leaf steel springs. BMW is using CFRP composites in their vehicle manufacture. The car body shown in Fig. 7a is of the 7 Series which is not just made of one type of material, rather it is a combination of metals and plastic. Figure 7b shows the Lamborghini Sesto Elemento made by the Italian automobile company Lamborghini and was launched in 2010. Some of the CFRP-made cars are Chevrolet Corvette Z06 (2016), Dodge Viper (2016), Ford Shelby GT350R Mustang (2016), Alfa Romeo 4C (2016), Ford GT (2016), BMW 7 Series (2016), Audi R8 (2017), and Lexus LC 500 (2017).

Fig. 7 Use of CFRP composites in automobile applications: a BMW 7 series [11] and b Lamborghini Sesto Elemento [12]

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1.4.5

159

Defence Applications

Composites possess the material characteristics appropriate for the fabrication of defence products. Companies like MFG have a strong record of successfully building FRP products for government agencies such as DARPA (USA) as well as prime and sub-contractors. Some of the desirable features include weight reduction, corrosion resistance, part consolidation, and prototyping. Some of the defence products include (FRP Defense Products—Suvarna Fibrotech Pvt. Ltd.) • • • • • • • •

FRP Defence Shelter for High Altitude Bel Box FRP Cabin FRP Winder Tape FRP Bio Digester FRP Pressure Pad cover FRP Bunkers FRP Toilet Cabins. The advantages of composite material as a defence product are listed as follows:

• • • • •

Rustproof and waterproof. Can be used in earthquake-prone areas. Easy to erection because of its unique panel tracking. Fire retardant. Skilled or semi-skilled workers can erect the shelter with the help of a panel tracking system and its erection manual. • Easy to transport because of lightweight. Figure 8 shows Personnel Armour System for Ground Troops (PASGT) vests and helmets made up of Kevlar fibre being used by U.S. servicemen during the invasion of Grenada in October 1983, the first combat usage of the PASGT system. Other Applications • Fibreglass Rebar GFRP Fibreglass rebar composite materials are manufactured for highways and other civil structures. FRP composites can be a promising option as they can replace conventional materials. Figure 9 shows some of the types of FRP rebars that are currently manufactured [14]. • Bus Stand New bus stops are being constructed to help the network of the urban transport system. Even the surfaces of roads at the bus stops are being made of fibreglass– concrete slabs. It is expected that the bus stops which are built with epoxy-coated and untreated steel rebar get corroded in about 10–15 years and hence, major restoration work is required periodically. Concrete slabs reinforced with Fibreglass Rebar are

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Fig. 8 PASGT helmets and vests being used by U.S. servicemen [13]

Fig. 9 Stronger, lighter, and durable GFRP rebar for constructions [15, 16]

expected to stay in good shape even after 100 years. Figure 10 shows a bus stand incorporating the concept of using FRP as a structural material.

1.5 Global Scenario There exists a series of pioneer industries and research teams worldwide dealing with FRP composites for various technical applications and solutions. In many of the developed countries, full-fledged applications of FRP composites in various sectors, such as automobile, railways, aerospace, marine, sports, and defence can be readily observed. Renounced industries like Boeing, Airbus, BMW, Mercedes, and others are very much inclined towards the use of more FRP composite components in the aerospace and automobile sectors owing to the exceptional specific strength and modulus of the FRP composites. World-class research facilities with focused projects on FRP composites at various universities are also driving the composite materials from laboratory to real-time applications. Some of these reputed research

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Fig. 10 Bus stand made up of FRP [17]

labs are Composite Construction Laboratory at EPFL, Switzerland, headed by Prof. Thomal Keller, Intelligent Composite Materials and Structures Lab at The University of Tokyo, Japan, headed by Prof. Nobuo Takeda, Bristol Composite Institute at University of Bristol headed by Prof. Michael Wisnom, and Center for Composite Materials at University of Delaware.

2 Trends and Drivers Efficient structural materials, robust and corrosion-resistant, contribute to the economy and result in a better quality of life both locally and nationally. Constructions using FRP composite with proper consideration of natural disasters, authentication of structural fidelity, and energy-saving materials are the current focus on structural applications. The lifespan of FRP materials is expected to be anything between 50 and 100 years, though predicting durability over such a long period is difficult. Currently, expectations are based on traditional, accelerated ageing methodologies, which are not truly representative of actual environmental conditions. Unlike metallic materials, there is still a lack of well-developed test procedures for FRP composites used in construction, railways, and so on. Also, other factors which are a matter of concern for the manufacturers are quality assurance and standardization [18]. The key driving factors for the global acceptance of FRP composites as a trending structural material are as follows:

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High modulus-to-weight ratio and strength-to-weight ratio Wide range of selection of raw materials as per the application requirements Intrinsic resistance to weather and the corrosive effects of salty air and seawater Improved fatigue resistance Rapid installation at site for footbridges, platforms for oil, and gas industry Low maintenance Ability to be tailored to needs.

2.1 Immediate Term (Up to 2020) The immediate use of fibrous polymeric materials may be in water/sewage pipelines, electric poles, portable cabins, and toilets as a lot of modernization projects are being executed in various cities in the Smart city mission. Polymer composites from renewable resources have also received increased attention over the past few years due to environmental matters and the fast depletion of traditional energy resources. In plastic waste disposal and recycling, fibre-reinforced plastic as a subclass of plastics has given rise to a number of disputes and disquiets. FRP is logically expected to gain environmental sensitivity as new more eco-friendly matrices such as bio plastics and UV-degradable plastic come to the fore.

2.2 Medium Term (2020–2025) Nowadays, the demand for both lightweight and durable materials has been the core driving vigour for the fast growth of polymer-based composites. Glass FRP involves comparatively lower energy during the manufacturing process as compared with metallic counterparts; it is more durable and has much lower thermal conductivity. The proposed future use of advanced fibrous polymeric composites may be its usage in combination with the more conventional materials like steel and aluminium. FRPs can be functional to reinforce the bridges, beams, columns, and slabs of buildings as shown in Fig. 11. It is likely conceivable to increase the strength of structural members even after they have been harshly affected due to several loading conditions. The dented reinforced concrete members would first involve the overhaul of the member by taking out the loose debris and filling in cracks and cavities with epoxy resin or mortar. For seismic strengthening of the reinforced concrete members, Fibre-reinforced polymer composites are advantageous over conventional materials, which pose impediments such as handling of heavy steel and the peril of corrosion. In addition, visually examining the condition of a concrete member following a seismic event is impossible. The driving force for using FRP is its dimensional stability, better seismic resistance, high stiffness and strength-to-weight ratio, the ability of tailoring the sturdiness

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Fig. 11 A strip of FRP composite reinforced to the deteriorating concrete bridge [19]

and mechanical features of FRPs. The polymer in the FRP composites guards the inner reinforcement against corrosion/rust as they can efficiently endure the severe environment [20]. Fibre-reinforced Phenolic resins are used in a varied array of applications, comprising electronics, aerospace, rail, mass transit, offshore water pipe systems, and ballistics and mine ventilation. Phenolic resin-based polymers are used for high temperatures as they have admirable heat resistance, chemical resistance, flame retardance, and electrical non-conductivity features [21].

2.3 Long Term (Beyond 2025) FRP can be used for high-performance structural components in space applications, particularly for space shuttle launch vehicles. The implementation of Nanocomposites will be the future trend as it requires a massive amount of investment. Therefore, before investing in the field of nanotechnology, we have to execute immediate and medium-term projects efficiently. Grouping nanotechnology with fibrous polymeric composites can be an encouraging tool to attain environmental sustainability. In a marine environment demanding corrosion resistance and lightweight compared to metallic structures, FRP materials offer fabulous potential. Attempts and policies therefore must be taken to prioritize the application of FRP composite in various naval applications.

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3 Industrial Capability The following challenges can be highlighted in contrast to the development of Indian FRP industries: • • • • • • • • • • • •

Availability of quality raw materials High price sensitivity of the market, combined with rising raw materials costs Lack of skilled labour to handle FRP Lack of awareness on composites in the Indian industrial world Quality assurance and standardization for manufacturers Lack of concrete regulatory bodies/framework A limited number of scientific publications Dependency of Indian industries on import of Carbon Fibres Moderate IP activities and IP management Lack of recycling policy of FRP waste and end-of-life products Necessity to develop Quality consciousness among small-scale FRP/GFRP composite manufacturers Need for faster development of new products and applications. Moderate to weak implementation of the automated fabrication process for FRP Lack of government policy and initiative to compete with global market.

3.1 Immediate Term (Up to 2020) The first and foremost critical problem the FRP industry is facing in India is the higher cost of raw material as compared to the international market; this adds up in the price of the product, which adversely affects the cost competitiveness of FRP products in contrast to products manufactured from conventional materials. Bulk import of the raw materials may not be affordable for many small-scale FRP industries hence, the supplier should open outlets in India to stock material at affordable prices. India needs more raw materials manufacturing industries to be set up in the country, including producers of glass fibre, specialty resins and chemicals, and styrene monomer. Engineers and the general public should be made aware of the superiority of FRP over conventional materials and build up their trust in it. Though today, several players are involved in the production and development of FRP composites, industrialization in FRP requires human resources training, design, mould design, and mould making; these services should be taught and nurtured at different workshops and institutes. Fabrication processes should be automated to reduce the need for skilled labour and to improve the quality as well as to boost the production rate. There is a need to build a ‘Closed Loop Composite system’ incorporating academia, suppliers, and industry. Composite labs should be set up in select educational institutes, for building up the employable human resources ready for the composite sector. Areas like Hybrid composites, Nanotechnology, and Automobiles may be explored depending on raw material, fabrication resources, infrastructure, and quality assurance tools. Already

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the sports sector globally is providing a vast market for FRP; however, in India, most of these needs are met by import, which adds to the cost. Hence, there is an immediate need for homemade sports equipment with lower price. Even big industrial houses like TATA and Reliance have started exploring FRP composites in many sectors like aviation, automobile, defence, electrical and electronics, industrial and municipal piping, infrastructure and disaster management, mass transportation, oil and gas, power and renewable energy, shipping, and telecommunication. In the architecture sector, FRP is an excellent material for domes, skylights, and doors; industries like Technocraft (Chennai) already have a strong foothold in these applications.

3.2 Medium Term (2020–2025) Different standards related to fabrication, design, and tests are to be put in place to ensure uniform standard/quality of the FRP products. Globally, India stands as the fourth largest market in installed wind power capacity. Currently, there are more than twenty local manufacturers in India who are working in this field, Suzlon Energy Ltd. being the largest, known all over the world for the production of the wind turbine generator. The Indian government has targeted harvesting of 60 GW of wind energy by 2022, from a figure of 24 GW in 2015. The ideal locations for wind energy harvesting, on the consideration of higher annual average wind speed, can be the western coast of Karnataka, Tamil Nadu, Kerala, Maharashtra, Gujarat and plains of Rajasthan, Gujarat, and Karnataka. Indian railway has been spending a massive amount on the renewal of track circuiting, rolling stocks, new lines, old tracks, bridges, signalling, upgrading of current trains, and manufacturing of new models; for all these applications, FRP can be the solution. Mobility Solutions Limited (MSL) is a large manufacturer of coach components in India. For Chennai Metro, 9 trains were imported from Brazil and 33 will be produced at the newly built Alstom plant in Sri City, Andhra Pradesh. For Mumbai monorail, train celling which is one of the crucial components was manufactured by DK composites of Malaysia. Hence, the Railway sector will be a booming market for the new local FRP industries. Many automotive industries acknowledge FRP for its superior crashworthiness and lightweight (improving fuel efficiency). Once the raw material price becomes affordable, its implementation will not remain only for luxury and sports vehicles. Rather, these materials can be used in low and mid-range cars and undoubtedly, it will promote FRP industries to produce a higher quantity of raw materials for the automotive sector. The Indian road network is the second largest in the world, where new roads and related infrastructure are required to manage increasing numbers of automobiles on the road. FRP industry can find a way in this too with FRP rebars, laminates, sheets, profiles, and panels. Also, these activities are helping the FRP piping industry to flourish [18].

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Nanotechnology provides significant opportunities for the development of sustainable, innovative materials for agriculture, water treatment, food production, processing, and preservation and packaging applications. However, our knowledge in the field of nanomaterial toxicity is limited; there is therefore a vital need for the prior consideration of the food contact safety implications of this technology.

3.3 Long Term (Beyond 2025) The aerospace sector is growing fast, and many industries are getting into composites not only to meet Indian requirements but also for the global market. Growth is also anticipated in the military aviation sector. In the marine industry, the Indian navy needs to update its defence system with more frigates like INS Vikramaditya to compete with other countries. These massive ships will require an enormous amount of FRP composites, which will open a vast market for FRP. Many industries from India export FRP products; a few of them are listed in Table 3 [18].

4 Market Growth Recently on a per capita basis, the consumption of composites has reached around 0.3 kg in 2018 from 0.25 kg in 2012 in India; still, it is much below compared to 2.5 kg in China and 11 kg in the USA. This 0.3 kg was possible due to the growth in the market, driven by Mass Transportation, Electrical and Electronics, Infrastructure, Building, and Construction. It is projected that the consumption of FRP composites may rapidly reach 4.9 lakh tonnes by 2022 rather which was 3.6 lakh tonnes in 2018 [22]. Based on the last five years, it is forecasted that FRP consumption will rise from a CAGR of 5.9% between 2013 and 2018 to a CAGR of 8.2% from 2019 to 2023 [23]. As shown in Fig. 12, in 2018, six major industries amounted to 82.1% composite consumption of total volume in different applications/sectors.

4.1 Immediate Term (Up to 2020) Shortly, there will be a definite replacement of conventional materials by FRP composites due to its numerous applications, which will boost its market in different sectors all over the globe. Subsequently, this will propel the need for a high amount of raw materials (fibre, polymer, and additives) and their production needs to be increased by several times to satisfy future demand. In the case of fibres, Glass fibres are highly used reinforcement materials contributing to a market share of 98.5% (Fig. 13). In India, Carbon and Aramid fibres are the most import-dependent

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markets. Still, a few local industries are producing these fibres, which can motivate new ventures to compete in this sector due to the lack of strong competitors. Application of Aramid fibres lies mostly in bullet-proof jackets, and that of carbon fibres lies in Defence, Aerospace, Sporting goods, and Automobile sectors which provide multiple opportunities for marketing [22]. In the case of resins, unsaturated polyester resin has seen a considerable consumption corresponding to 83% of the total Indian composites market whereas epoxy resin has only 10% contribution due to its high cost, but due to its exceptional properties, this consumption will increase in future. Table 3 Industries from India exporting FRP products Indian companies

Main composites products/expertise

Main countries for export

Devi Polymers Pvt. Ltd., Chennai (Est. 1975)

Glass-reinforced plastic (GRP)/sheet moulding compound (SMC) panel-type water tanks; GRP/SMC enclosures; GRP/SMC canopies; OEM products

Middle East, the USA, the UK, South Africa, etc

Composite Designs & Technology (CDT)/Epsilon Composite Solutions (ECS), Pune (Est. 1999)

Product design and process engineering of composites, for infrastructure, architectural, transportation, marine, and corrosion applications

Singapore, Bahrain, Japan, the UK

Gandhi and Associates, Vadodara (Est. 1972)

Anti-corrosion applications, process equipment

Middle East, Europe

Industrial & Commercial Enterprises, Pune (Est. 1988)

Skylights and structural fibre-reinforced plastic (FRP)

Kamak Plastics Pvt. Ltd., Chennai (Est. 1964)

Wind turbine covers, textile machinery covers, cabins, motor covers, tanks, etc

Kineco Pvt. Ltd., Goa

Design and manufacture of The USA, Europe composite products for rail, automotive, and petrochemical industries, including pipes, boats, underground storage tank

Mechemco Industries, Mumbai

Manufacture of polyester resins, vinyl ester resins, speciality resins and gel-coats, and also resins for solid surface and casting

Naptha Resins and Chemicals Unsaturated polyester resin, Pvt. Ltd., Bangalore (Est. vinyl esters, phenolic resins, 1974) polyester pigments, gel-coats, filled resins, putty resins (continued)

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Table 3 (continued) Indian companies

Main composites products/expertise

Main countries for export

NTF (India) Pvt. Ltd., Manesar (Est. 1996)

Interior and exterior panels for The USA, Italy, Japan, Spain automotive, railway coaches, locomotives, wind turbines, commercial vehicles, farm equipment, and construction equipment. Expertise in resin transfer moulding (RTM), Light RTM, vacuum-assisted RTM, MIT, SMC, hand lay-up, and thermoplastic composites. Polyurethane composites by RRIM. Painting of thermoset and thermoplastic parts with polyurethane paints solvent and water-based. In-house engineering capability from product concept to production

Resadh Group: Satyen Polymers; Marketing International, Mumbai

manufacturer of unsaturated polyester resins, all grades; Marketing International—distributor for Magnum Venus Plastech, exporter of designed/fabricated equipment and turnkey projects

Sintex Industries Ltd., Kalol

Roto moulding, blow moulding, The USA, Australia, Africa, thermoforming, SMC, Middle East, Europe pultrusion, prefabs, BT shelters, hand lay-up, FRP underground tanks, etc

The UAE, Saudi Arabia

Regarding specific FRP markets in India, FRP pultruded profiles have gathered enormous attention from the public due to their applicability in various sectors. One could even find complex shapes and sizes of pultruded profiles, which prove challenging to be obtained from conventional materials (Fig. 14). Industries are turning towards FRP profiles due to their high strength, high impact strength, high durability, high performance, lightweight, lower shipping, handling and installation costs, lower operational energy demand, minimal maintenance costs, and prolonged life. It has various applications which also provide a vast market for this product, as shown in Fig. 15. An estimation of $3.4 billion is expected to be reached by the global pultrusion market by 2025. It is forecasted that the utilization of the pultrusion process will grow at a CAGR of 3.7% from 2019 to 2025 (Fig. 16). Being a quick manufacturing process simultaneously having good productivity, the Indian Composite Industry can gain huge profits by employing this process on a large scale.

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20.50%

Mass transportation 14.20%

Building and construction

13.80%

Electrical and electronics

12.30%

Renewable energy

11.40%

Infrastructure

9.90%

Chemical/corrosion Telecom

6.40%

Military & Defence

6.30% 4.20%

Technical textile 1%

Others 0%

5%

10%

15%

20%

25%

Fig. 12 Indian composites market by applications in 2018 [22]

Fig. 13 Percentage representation of consumption of fibres and resins in Indian market [22]

Fig. 14 Some FRP pultruded profiles [24]

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Fig. 15 a Pultruded truss bridge [25] and b Pultruded GFRP profiles in railways [26]

Fig. 16 Global pultrusion market (2014–2025) [27]

As a part of the Smart City Mission of the present government under the urban planning scheme, the market of developmental infrastructure work is in high demand all over India. In 2018, Building and Construction industry turned out to be the second largest consumer of composite components amounting up to 14.2%, while infrastructure amounted up to 11.4%, as can be seen in Fig. 1. On 1 February 2018, Finance minister Mr. Arun Jaitley tabled the economic survey during the 2018 budget presentation and said that till 2040 India would require a $4.5 trillion investment to develop infrastructure. In the backdrop of such huge investments, the Indian composite industry will gain attention not only for the aesthetics but also for smart city projects. To cope with such big plans, there is a need to renovate and strengthen the old and deteriorated columns and structures with FRP composites (Fig. 17). The complex structures made of FRP (Fig. 17a) is used for cladding, as seen in the superstore in Bristol, UK (Fig. 17b), FRP modular classrooms which are future classrooms of which the project and design are done by Future Systems Architects and CETEC

Fig. 17 a FRP-strengthening of structures [28], b Superstore, Bristol, UK, and c FRP future classrooms [29]

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in the UK (Fig. 17c). These are some of the prospective and promising applications of FRP composites in building, construction, and infrastructure for India. The piping industry is also one of the stakeholders who will greatly profit from all these new constructions. The use of filament-wound composite pipes is on the rise with growing demand from marine, water and wastewater sewage, oil and gas, chemical, pulp and paper, and retail fuel. As reported by Lucintel, the market for pipes and tanks from 2016 to 2021, is shown in Fig. 18. FRP composites hold huge potential for use in offshore structures, thanks to the inherent qualities like resistance against extreme environments, contaminated contexts (chemical and biological), and also risks of earthquakes (Fig. 19). The market for FRP rebar (Fig. 20a) lies in applications like marine structures, bridges and tunnels, water treatment plants, electrical isolation, MRI rooms, roads, and others. The demand for FRP rebars for use in water treatment plants and electrical isolation applications is the primary driver of the FRP rebar market in the coming years. Electrical and electronic applications such as PCB, breadboard, and insulators can lead to substantial immediate growth since, in 2018, it was the third largest consumer of composites (Fig. 20b). India being the second largest consumer of LPG can contribute to an enormous share of Indian Composite Industry once steel LPG

Fig. 18 Growth opportunities of pipes and tanks in Indian market in 2016 to 2021 [30]

Fig. 19 Offshore FRP a platform [31] and b storage tanks [32]

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Fig. 20 a GFRP rebars, b PCBs made up of GFRP [33], and c Composite LPG cylinder [34]

cylinders are gradually replaced by composite LPG cylinders (Fig. 20c) since many limitations are associated with steel LPG cylinders. In 2016, prompted by its property of anti-explosion in cases of fire or leakage and also its lightweight for easy carriage, HPCL had placed 5000 orders of composite cylinders in 2016. In the backdrop of the current Swachh Bharat Mission, modular toilets are making an enormous market. These modular toilets made from FRP composites are lightweight, dust-free, and dirt-free. FRP Composite manhole covers can have a significant market in India due to their tremendous advantages like reduced weight leading to reduced worker injuries, stay where they should be, i.e., locked into place, are fully traffic rated, can reduce inflow and infiltration in sewers, are ideal for corrosive environments, and can reduce odours. Nuts and bolts from FRP composites have high demand in applications concerning high corrosion resistance (Fig. 21a). FRP poles, being lightweight, corrosion-resistant, and available in different lengths

Fig. 21 a FRP fasteners [35]. b FRP poles [36]

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are being increasingly deployed for utility transmission and distribution applications (Fig. 21b). In the Sports market too, we can find wide applications of FRP composites like skating board, badminton racket made of hybrid FRP composites, baseball bat, and many more (Fig. 22). Germany has witnessed a large market of composites in the sports sector, as seen in Fig. 23. Mostly, carbon and glass fibre are used in the manufacture of sports equipment. The demand for durable materials for rackets, hoverboards, and skis will drive the growth to a much higher level. Products that increase the strength and drive in golf clubs and hockey sticks, decreasing the overall weight, will increase the carbon fibre demand. These can augment the market in India too to a smaller degree. Domestic products like dustbins, tables, and chairs can contribute to Indian Composite Market massively (Fig. 24). To attract children in general, children’s parks can be installed with FRP structural equipment, which are robust, lightweight, and corrosion-resistant, further boosting the market of FRP materials (Fig. 25).

Fig. 22 a Skating board, [37]. b Badminton racket, and c Baseball bat: all made of FRP composites

Million USD

Fig. 23 Sports composite market revenue of Germany by material, 2013–2024 [38]

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Fig. 24 a Dustbin, b Chair, and c Table

Fig. 25 Outdoor park equipment

4.2 Medium Term (2020–2025) With the Indian automotive industry rapidly booming and the industry in itself witnessing a gradual transition from the conventional metallic structures to the lightweight and fuel-efficient FRP structures, it can be rightly said that the future belongs to the FRP industry with tremendous growth opportunities lying in store for it. In 2018, in India, the largest user of Composite components was the Mass Transportation Sector amounting to a share of 20.5% (Fig. 12). However, at the global stage, several automobile manufacturing companies have already tapped into the considerable potential of FRP. The market of FRP composites in the Railway sector ranges widely, starting from applications like FRP window, FRP window frame, composite brake blocks for railway coaches, FRP ceiling panels, side panels and lavatory panels for coaches, lavatory modules for LHB coaches, set of FRP component for LHB chair car coaches, entrance door of coaches, FRP gear case for locomotive, railway cross ties/sleepers (Fig. 26a), and railway platform (Fig. 26b). For the security and safety of the country, FRP composites can be extensively used to develop bullet-proof vests made up of synthetic Fabrics, FRP helmets, FRP safety masks, and rifle components (Fig. 27). This sector consumed 6.3% of FRP composites in 2018, in India (Fig. 12), which will further increase shortly. To enhance the security of soldiers during hostile situations, FRP composites play a vital role in developing impact-resistant armoured vehicles, Tanks, and Desert Patrol Vehicles (Fig. 28). Portable Bridge Armoured vehicles, made of FRP composites, can be deployed to have access to remote areas, since they can negotiate the paths easily and quickly. The same is the case with rescue and patrol boats (Fig. 29).

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Fig. 26 a FRP cross ties [39] and b FRP platform Chicago [40]

Fig. 27 a Bullet-proof vest, b FRP helmets, c FRP safety masks, and d Rifle components

Fig. 28 a Armoured vehicle, b Tank, and c Desert patrol vehicle

Fig. 29 a Portable bridge armoured vehicle, b Rescue boat, and c Patrol boat

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Dedicated to the nation, the INS Vikramaditya is a modified Kiev-class aircraft carrier. The concept of stealth technology is used to build the frigate whose superstructure is entirely made of composite materials, as Fig. 30 shows. India at present has only two operational aircraft carriers compared to the US, which has eleven. It is likely that India will build a bigger fleet requiring a massive amount of raw material, which should boost the market for raw materials. The growth of composites in India is also substantially dictated by the Renewable energy sector too. Wind energy is widely viewed as one of the common future energy alternatives, which is being harnessed currently at many locations worldwide and plans are in place to upgrade the wind energy generation by manifold in the future. As such, a large range of opportunities opens up for the use of FRP in wind turbines (Fig. 31b), an area that can be exploited by the big players of the FRP industry. India

Fig. 30 INS Vikramaditya serving Indian Navy

Fig. 31 a Composite houseboat, b FRP nacelle cover on Wind Turbine, and c Diamond DART 450

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has one of the largest installed capacities for wind power generation and can act as a great market for FRP-based wind turbines. Wind Energy in India has touched a milestone in 2017 by installing 4148 MW of capacity which was 20% more compared to 2016. There is an estimated prediction that India will be seeing 60 GW of wind energy capacity by 2022 [41]. As the wind energy sector capacity increases, it will correspondingly provide growth to the Indian composite industry. Currently, India ranks 4th in overall installed capacity (35 GW) of wind energy, while China tops the list with 221 GW of installed capacity followed by the USA and Germany.

4.3 Long Term (Beyond 2025) The aerospace sector is growing fast, and many industries are getting into composites not only to meet Indian requirements but also for the global market. Many companies are getting their production outsourced from Europe and the USA. India being one of the largest growing aviation markets in the world holds massive potential for FRP market growth on a long-term basis. The domestic aerospace industry, when fully developed and capable of meeting internal demands, can serve as a single major contributor to the market growth of the Indian FRP industry. However, many of the aerospace giants such as Boeing, Airbus, and Textron have already shifted to the use of FRP-based components from the traditional ones. The marine industry is another field that contributes to a large share of the Composite industry. Tourism is in high demand, and people are drawn by the aesthetics and appearance, as shown in Fig. 31a. This feature can only be provided by FRP composites. In Fig. 31c, Diamond DART 450 aircraft is shown which is built predominately from carbon fibre. Shortly after World War II, boat construction was the first marine application of FRP composite. Ship hulls are also made up of FRP composites (Fig. 32). Telecom Industry is an emerging field consisting of communication antennas, microwave applications, and radomes, (Fig. 33). In 2018, the Indian telecom industry represented 6.4% consumption of the total FRP volume. Radomes (weather-proof structure protecting radars) being an essential structural component in aircraft and warships will have a massive market in the years to come.

Fig. 32 Ship hull made of FRP composite

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Fig. 33 a Application of FRP in Radomes, b Communication antennas, and c Microwave application

Fig. 34 a Suspension bridge across the Mississippi in the US [42]. b Dragon Bridge in the UK [43]

FRP Bridges are well established and accepted in countries abroad; in the US, a suspension bridge built across the Mississippi River was revitalized by Kevlar/glass/epoxy composite (Fig. 34a). Also, a famous lifting bridge in the UK known as Pont y Ddraig (Dragon Bridge) connecting Conwy and Denbighshire over the river Conwy was built in 2013, wherein two wings that rise at the same time for letting the boat traffic to pass were made up of FRP composites as shown in Fig. 34b.

5 Research and Development/Academia Engineers throughout the world, including India, have been using FRP composites to solve their structural problems. As compared to other countries, a few researchers in India are focused on trying to enhance the mechanical, thermal properties and environmental durability of FRP composites by using various methods like fibre modification (using different techniques to modify the fibre surface to improve adhesion), matrix modification (addition of additives, fillers in matrix), and hybridization

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of both fibre and matrix. The following list gives a summary of the researchers and industrialists who are working on FRP composites in India are listed in Tables 4 and 5.

5.1 Immediate Term (Up to 2020) Most developing countries thrust rapid industrialization, export improvement, selfreliance and diminishing the import in order to attain a strong economy. The government should provide exclusive economic benefits for industries for development in the field of composites and also develop R&D centres with fullfledged working facilities starting from fabrication to characterization facilities. Industrial experts and academicians should attempt to conduct various joint conferences, seminars, and workshops on these materials due to which the public will get awareness. Easy and accurate techniques have to adopt for the fabrication of micro to macro composite parts from developed countries and also implement various techniques for recycling and reuse of FRP composite. As this material needs a kind of inter-disciplinary approach, dedicated courses of FRP Composites should be offered to UG and PG students in various departments (Civil, Metallurgy, Mechanical, Aerospace, Chemical, and so on) in all the IITs, NITs, and other universities. An R&D initiative needs to be conducted by institutions like IISc, IITs, NITs, and other Indian universities simultaneously by creating awareness among the general public about composites. As producing an FRP composite components for a specific application requires stringent selection of materials, deciding the volume fraction of the constituents, orientation, and distribution of the reinforcement in the composite by specialized fabrication techniques and quality assurance through proper macro- and micro- characterization techniques, dedicated research labs must be set up in order to bring the academic and industrial personnel together to a common platform. An additional advancement in the field of composites can be achieved by training Indian engineers and designers in the R&D labs and industries based on Composite Materials set up in various developed countries.

5.2 Medium Term (2020–2025) Collaboration between industries and universities is highly essential in the field of FRP composites. The following collaboration works are needed for developing the FRP composites in India. • Support services like software, design, prototype development, etc., can be outsourced from India, as many international companies are doing in the case of general engineering.

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Table 4 Researchers and industrialists who are working on FRP composites in India Name

Designation/Organization

Area/Expertise

Prof. S. Gopalakrishnan

Professor, IISc Bangalore

Carbon nanotube and graphene-based multi-scale composite architecture for improved energy absorption in aerospace structures

Prof. Niranjan Krishna Naik

Professor, IIT Bombay

Strain rate effect on CNT-reinforced polymeric composites, low-velocity impact/ballistic impact behaviour of composites and hybrid composite

Prof. M. Ramji

Professor, IIT Hyderabad

Mechanics of composites, composite structures, and repairs

Dr. Kamal K. Kar

Professor, IIT Kanpur

Use of carbon nanomaterials in polymer composites, nanocomposites including multiscale composites

Dr. P. Alagusundaramoorthy

Professor, IIT Madras

Analysis and design of advanced composite structures condition assessment, repair and strengthening of concrete, steel and masonry structures using FRP composites, and other materials

Dr. V. K. Srivastava

Full Professor and Coordinator Nondestructive Evaluation of of Composite Materials (IIT composite materials, toughness BHU) of fibre composites

Dr. Arun Kumar Pradhan

Associate Professor, IIT Bhubaneswar

Prof. B. C. Ray

Professor HAG, NIT Rourkela Effect of environmental parameters on the structural durability of FRP composites

Dr. R. K. Prusty

Assistant Professor, NIT Rourkela

Synthesis of advanced Fibre-Reinforced Polymer (FRP) composites

Dr. C. M. Manjunatha

Senior Principal Scientist CSIR—National Aerospace Laboratories, Bengaluru

Fibre-reinforced composites, nanocomposites, fatigue and fracture mechanics, damage tolerance evaluation, mechanical testing, and evaluation

Composite materials and structures

(continued)

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Table 4 (continued) Name

Designation/Organization

Area/Expertise

Dr. Bhanu Pratap Singh

Senior Scientist in CSIR National Physical Laboratory, and Assistant Professor (AcSIR)

Large-scale synthesis of carbon nanostructures and their advanced nanocomposites for structural applications

Dr. Krishna M

Professor, R V college of engineering, Bengaluru

Microwave-assisted manufacturing process for polymer composites, nano powder-filled conductive polymer composites for space applications

Dr. Dinesh Kumar Rathore

Assistant Professor, KIIT Bhubaneswar

Nano-filler modified fibre-reinforced composites for structural applications

Dr. N. G. Nair

Founder, Proprietor, Chief designer, and Consultant of NGN Composites

Areas of expertise include composite materials research and development, process development, process modelling and process design, composite materials science, structural mechanics and design, design of composite products, and testing and quality control

Dr. A. Selvam

Executive Secretary, FRP Institute, Chennai

Collaboration with the industries and institutions for upgrading the composites technology and to promote the growth of the Indian composites industry

Table 5 Mechanized composite production facilities in India [6] Type of facility

No. of units

Installed capacity (tpa)

Filament winding

15

15,000

SMC manufacture

6

20,000

Pultrusion

8

10,000

Compression moulding

20

20,000

Automated grids/grating making machine

1,000

Vacuum-assisted resin transfer moulding (VARTM) 15

30,000

FRTP* pellet making plants

10 big, 20 small 35,000 +

FRTP* injection moulding

>150

* FRTP

= Fibre-Reinforced Thermoplastic

n/a

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• Foreign companies importing raw materials can start their outlets, and later, as the demand grows, they can establish their manufacturing facilities in India. • Products can be manufactured in India, either under buy-back or under joint venture arrangements with Indian industries. • Infrastructure like mould and machinery fabrication can be developed in India for the Asian region.

5.3 Long Term (Beyond 2025) Raw materials manufacturing facilities need to be established in India, including producers of glass, carbon, and Kevlar fibres as well as specialty chemicals, nanofillers, and a wide range of polymers. Seamless knowledge transfer from research to real-time applications of FRP composites must be channelized through the commercialization of innovative technologies. Generally, raw materials prices are higher in India than in the international market, so the establishment of composites industries in India becomes a must in the long run [4]. Owing to stringent environmental reasons and policies, recycling and reuse of defective, waste, and end-of-life components are becoming an unavoidable technical challenge ahead of all the industries. In this regard, a proper and in-depth research is also a need of the hour dealing with such recyclability issues of FRP composites. Hence, government should initiate funding drives to encourage researchers working in this field to take up this new challenge and come up with possible ways to recycle and reuse various types of waste FRP composites.

6 Conclusions Based on the techno-commercial aspects of fibre-reinforced polymer composites, the following conclusions may be drawn from the present study: • FRP composites are the trending materials of the century with optimum combination of structural property requirement, such as strength, modulus, density, fatigue, and corrosion resistance with a wide scope of tailorability. • There exists a broad application spectrum of FRP composites ranging from constructions, marine to aerospace and defence applications. • India being a fast-developing country, there is a massive requirement of strategic development and production of composites to fulfil the requirement of the hour. • Several projects such as manufacturing FRP water and oil pipelines, water tanks, electric poles, portable toilets, and cabins may be taken up under various smart city projects. Further, with a gradual increase in production capacity and maturity in handling bigger projects, medium/long-term projects may be focused on extensive use of FRPs in bridges, railways, automobiles, and so on.

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• In order to make a competitive FRP market in India, industries also need to look after the production of raw materials such as different types of advanced fibres and polymers. Another technical issue which must be dealt with with utmost care is the recycling and reuse of discarded and end-of-life industrial and commercial products. • Several attempts and drives have been initiated by various small- and large-scale industries in India to enter into the FRP business looking at the forecasted largescale demand of these materials in almost all structural sectors with a primary focus on transportation and construction. • Looking at the forecasted future market, special attention should be given to offering a dedicated inter-disciplinary course on ‘Composite materials’ in technical institutions to diploma, degree, and post-graduation students. Initiatives in this regard are also required to establish research-oriented laboratories in various regions, maybe involving both academia and industries together. Acknowledgements We hereby express our special thanks and gratitude to the scholars of FRP Composite Lab at NIT Rourkela, viz. Mritunjay Hiremath, Sushant Saurabh, Shubham, Srinivasu Dasari, and Abhinav Fulmali for their support.

References 1. Material and Process Selection Charts n.d. 2. Composites Engineering Handbook. Taylor Francis n.d. https://www.taylorfrancis.com/books/ e/9780429175497 (accessed June 15, 2019). 3. P.K. Mallick, Fiber-Reinforced Composites : Materials, Manufacturing, and Design, 3rd edn. (CRC Press, 2007). https://doi.org/10.1201/9781420005981 4. First Ever Video Shows Cockpit of Top-Secret B-2 Stealth Bomber n.d. https://interestingengi neering.com/first-ever-video-shows-cockpit-of-top-secret-b-2-stealth-bomber. Accessed 27 Nov 2020. 5. Boeing: 787 Dreamliner n.d. https://www.boeing.com/commercial/787/. Accessed 27 Nov 2020. 6. N.G. Nair, Composite houseboat helps tourists explore India. Reinf Plast 49, 24–6 (2005). https://doi.org/10.1016/S0034-3617(05)70977-3 7. Visby-class corvette. Wikipedia (2020) 8. One Ocean Thematic Pavilion n.d. https://frameweb.com/article/one-ocean-thematic-pavilion. Accessed 28 Nov 2020 9. Concert hall composites: Acoustic alchemy n.d. https://www.compositesworld.com/articles/ concert-hall-composites-acoustic-alchemy . Accessed 28 Nov 2020 10. S. Reeve, Mini-high platforms and the ADA n.d. https://www.compositeadvantage.com/blog/ mini-high-platforms-and-the-ada . Accessed 25 Feb 2020). 11. read JSA min. How BMW Utilise Composites to Manufacture Its New 7 Series. Compos Today 2015. https://www.compositestoday.com/2015/06/how-bmw-utilise-compos ites-to-manufacture-its-new-7-series/. Accessed 28 Nov 2020 12. Lamborghini unveils Sesto Elemento carbon fibre concept car. Mater Today n.d. https:// www.materialstoday.com/composite-applications/news/lamborghini-unveils-sesto-elementocarbon-fibre/ . Accessed 25 Feb 2020

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13. procomp-bg.com. PASGT Standard. MARS Armor n.d. https://www.marsarmor.com/products/ combat-helmets/pasgt/standard-mbh-pasgt-std/. Accessed 25 Feb 2020 14. The Application of FRP Composites in Highway Infrastructure | TUF-BAR n.d. https:// www.tuf-bar.com/the-application-of-frp-composites-in-highway-infrastructure/. Accessed 15 Jun 2019 15. FRP Rebar: A Revolution in Concrete Construction n.d. https://www.aramcoexpats.com/art icles/frp-rebar-a-revolution-in-concrete-construction/. Accessed 28 Nov 2020 16. D. Admin, World’s largest GFRP rebar project embraces corrosion-free future. Pultron Compos. n.d. https://www.pultron.com/news-insights/worlds-largest-gfrp-project/ Accessed 28 Nov 2020 17. Fiberglass-reinforced Bus Stops, TUF-BAR n.d. https://www.tuf-bar.com/application/busstops/. Accessed 28 Nov 2020 18. A. Jacob, India’s FRP industry benefits from booming economy. Mater. Today (2007). https://www.materialstoday.com/composite-industry/features/indias-frp-industry-ben efits-from-booming-economy/. Accessed 13 Jun 2019 19. T. Bufford, Adding life to aging bridges, Infrastructure composites—CM Online. Compos. Manuf. Mag. (2014). http://compositesmanufacturingmagazine.com/2014/01/frp-compositesstrip-repair-flat-slab-concrete-bridges/. Accessed 28 Nov 2020 20. G. Oliveto, M. Marletta, Seismic retrofitting of reinforced concrete buildings using traditional and innovative techniques. ISET J. Earthq. Technol. 42 (2005) 21. J.A. Brydson, 23—Phenolic Resins, in Plast. Mater, ed. by J.A. Brydson, 7th edn. (Oxford: Butterworth-Heinemann, 1999), pp. 635–67. https://doi.org/10.1016/B978-075064132-6/500 64-4 22. Indian Composites Industry Outlook—HOME n.d. http://icerpshow.com/about-icerp/indiancomposites-industry-outlook/. Accessed 3 Jul 2018 23. Composites industry hopes to touch $2.5 billion by 2021—The Hindu BusinessLine 2018. https://www.thehindubusinessline.com/companies/composites-industry-hopes-to-touch-25billion-by-2021/article25821384.ece. Accessed 13 Jun 2019 24. FRP Pultruded Products Manufacturer. FiberTech Compos n.d. http://fibertech.co.in/frp-pultru ded-products.html. Accessed 27 Feb 2020 25. T. Keller, N.A. Theodorou, A.P. Vassilopoulos, J. de Castro, Effect of Natural Weathering on Durability of Pultruded Glass Fiber-Reinforced Bridge and Building Structures. J Compos Constr 20, 04015025 (2016). https://doi.org/10.1061/(ASCE)CC.1943-5614.0000589 26. Fiberglass pultruded profiles in the transport sector—Saimex s.r.l. Saimex Pultrusion n.d. https://saimex-pultrusion.com/pultruded-profiles-transport-mobility/. Accessed 28 Nov 2020 27. Global Pultrusion Market by applications, end use industry, material, and region 2018–2023| Lucintel n.d. https://www.lucintel.com/rb/pultrusion-market.aspx . Accessed 4 Dec 2020 28. Design of FRP Axial Strengthening of RCC Columns -ACI 440.2R-08 n.d. https://theconstr uctor.org/structural-engg/frp-rcc-column-axial-strengthening/16683/ Accessed 28 Nov 2020 29. D. Kendall, Building the future with FRP composites. Reinf Plast 51, 26–33 (2007). https:// doi.org/10.1016/S0034-3617(08)70131-0 30. Opportunities for Indian composites market 2016–2021 n.d. https://www.lucintel.com/indiancomposites-market-2016.aspx. Accessed 4 Dec 2020 31. Anti-Slip Marine Grating for Marine Applications. Dura Compos. n.d. https://www.duracompo sites.com/marine/fibreglass-marina-grating/grp-grating-marine-applications/. Accessed 28 Nov 2020 32. FRP Storage tanks for offshore industry. Plast Compos. n.d. /topics/frp-for-offshore Accessed 28 Nov 2020 33. Single Sided PCB, ICAPE GROUP n.d. https://www.icape-group.com/pcb/pcb-types/singlesided-pcb/. Accessed 29 Nov 2020 34. LPG Composite Cylinder Manufacturer : Time Techno Plast n.d. https://www.timetechnoplast. com/business-division/composite-cylinder/lpg-cylinder/. Accessed 28 Nov 2020 35. Composite fasteners—FRP bolts and nuts, Röchling Industrial EN n.d. https://www.roechlingindustrial.com/products/composites/gfrp-cfrp/fasteners. Accessed 4 Dec 2020

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36. FRP Poles FRP Pipe FRP Pressure Tank Kolkata India. FibroplastichemCom n.d. http://www. fibroplastichem.com/frp_grp_poles.html . Accessed 4 Dec 2020 37. Composites green surfing, skate boarding. Compos. Aust. n.d. https://www.compositesaustr alia.com.au/about_composites_australia/australian-composite-company-case-studies/compos ites-green-surfing-skate-boarding/. Accessed 4 Dec 2020 38. Insights GMR. Global market research insights report: sports composites market in manufacturing equipment is expected to bolster growth. Glob. Mark Res. Insights Rep. (2016). https://glo balmarketresearchinsight.blogspot.com/2016/07/sports-composites-market-in.html. Accessed 4 Dec 2020 39. Rail – an evolving market for FRP components, Mater. Today n.d. https://www.materialstoday. com/composite-parts/features/rail-an-evolving-market-for-frp-components/. Accessed 4 Dec 2020 40. Advantage C. Project Gallery—Rail Platforms—Chicago METRA Station New Lenox n.d. https://www.compositeadvantage.com/gallery/rail-platform-new-lenox. Accessed 4 Dec 2020 41. S.H. Kulkarni, T.R. Anil, R.D. Gowdar, Wind Energy Development in India and a Methodology for Evaluating Performance of Wind Farm Clusters. J Renew Energy (2016). https://doi.org/ 10.1155/2016/6769405 42. Fiber-reinforced plastic strengthens a bridge over the Mississippi. BasaltToday (2016). https:// basalt.today/2016/08/7118/. Accessed 27 Feb 2020 43. Composite materials: enter the dragon—The Manufacturer n.d. https://www.themanufacturer. com/articles/composite-materials-enter-the-dragon/. Accessed 27 Feb 2020

Present Status and Future Indian Perspectives of Advanced Fibre-Reinforced Composites for Structural Applications N. Eswara Prasad, Debmalya Roy, Suresh Kumar, and Dibyendu S Bag

1 Introduction 1.1 Composites and FRCs The term ‘composite’ in material science generally refers to a material system combining a matrix and reinforcing agents [1–5]. Composite materials have been used for a range of applications ranging from simple household items to lightto-heavy industrial and structural usages including state-of-the-art defence and aerospace products. Weight reductions and improved mechanical properties are the critical factors making composites the materials of choice. The performance and costs of the manufacturing and processing of composites used in recent times are crucial factors in materials technology. The excellent costto-performance benefits enable a growing market for industries like aerospace, automotive, manufacturing as well as the construction and marine sectors. The huge demand for large-scale production has witnessed the innovative and rapid growth of the composites industry and their use as alternatives to metals. Fibre-reinforced composites (FRCs) are a special type of engineering materials in which the low strength of the matrix is compensated and augmented by the introduction of high-strength fibres [4–8]. FRCs which are schematically shown in Fig. 1a can be broadly classified based on the types of matrix materials (Fig. 1b) and fibres and the lay-up designs (Fig. 1c) [4, 9–15]. FRCs possess a number of advantages in terms of superior mechanical properties and strength-to-weight ratios that have been schematically compared and represented by Ashby plots: these plots are compact and useful for initial material selections. The fracture toughness of FRCs critically depends on the fibre and matrix properties as N. E. Prasad (B) · D. Roy · S. Kumar · D. S. Bag Defence Materials and Stores R&D Establishment (DMSRDE), DMSRDE PO, DRDO, GT Road, Kanpur 208013, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_8

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Fig. 1 Schematic representation of FRC: a Different matrices; b Different morphologies of fibres, and preforms with popular weaving patterns (c)

well as the lay-ups of fibres and matrix. The fibres provide toughening of the matrix by promoting extensive crack bridging in the wake of a crack. The development of Linear Elastic Fracture Mechanics (LEFM) and lately advanced non-linear fracture mechanics, based on JIC , JR -G, and JC , provide an understanding of the reduced strengths of composites in the presence of flaws or cracks. Also, a range of analytical methods based on interfacial shear stress have been used to represent single fibre pulls out and fragmentation to estimate the adhesion between the rigid fibre and matrix.

1.2 Property Enhancement through Fibre Toughening Pre-existing manufacturing defects, stress concentrations, and impact with foreign objects are mainly responsible for structural failure in laminated FRC structures, and are represented by inter-laminar failures (delamination and debonding) [16]. The fibre bridging phenomenon leads to a slowdown of the delamination growth at the fibre/matrix interfaces and is schematically represented in Fig. 2. The mode I (tensile mode) plot of fracture toughness as a function of the crack length is known as a crack growth resistance curve. This curve provides quantitative insight into the fibre bridging phenomenon: more specifically, enhancement of the critical energy

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Fig. 2 Schematic of fibre/whisker-based unified toughening due to ‘crack bridging’, applicable mostly to the FR-CMCs with Long Fibre Reinforcements (see Section [3, 5])

release rate with respect to crack length quantifies the effects of fibre bridging in terms of toughening.

1.3 MMCs In Metal Matrix Composites (MMC), the reinforcing phase is generally particles, whiskers, short fibres, or continuous fibres. The common fibres for FR-MMCs are Carbon, Boron, Alumina, Silicon Carbide, Molybdenum, and Tungsten; and the metal matrix materials are usually ferrous or non-ferrous metals. There is a wide range of non-ferrous metals and alloys used, based on Aluminium (Al), Copper (Cu), Magnesium (Mg), Titanium (Ti), and Ni, with or without alloying. The choices for ferrous metal-based matrices are steel, cast-iron, and Fe-based superalloys [17, 18]. MMCs are generally fabricated by casting and powder metallurgy processes; see Fig. 3. (1)

(2)

In the casting method, a blend of reinforcing agents is mixed into the molten alloy matrix under atmospheric pressure, whereby the good wettability of reinforcing elements with the molten alloy phase is the key. In order to increase the wettability, a third alloy phase that has a mutual wettability with the molten and reinforcing phases is generally added. A recent manufacturing technique for MMCs is the infiltration of porous ceramic fibre-based preforms by a molten alloy under pressure. The powder metallurgy method for FR-MMCs is the predominant classical blending method of powder matrix and reinforcing agents, which are then subjected to cold pressing or sintering, followed by plastic working (forging, extrusion).

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Fig. 3 Representation of the casting and powder metallurgy process for making MMCs [19]

FR-MMCs offer higher moduli of elasticity, ductility, and resistance to elevated temperatures. They have been used in the electronic, automobile, and aircraft industries and are known for high strength, good wear resistance, and electrical as well as thermal conductivities. However, as the production costs of FR-MMCs are higher than those for the conventional composite materials, the focus and innovation in R&D are on property requirements, cost analysis, and future applications.

1.4 FR-PMCs Fibre-reinforced polymer matrix composites (FR-PMCs) are important, widely used, and continually promising lightweight and high-strength engineering structural materials nowadays. These are multi-component systems consisting of reinforcing fibres (inorganic fibres: E = 80–250 GPa; and also, high modulus organic fibres: E > 100 GPa) to impart strength to polymer matrices (E = 2–4 GPa in the glassy state) which act as binders to the fibres. The fibres and matrices are bonded to each other by weak intermolecular forces and/or by mechanical interlocking at their interfaces (chemical bonding is rarely involved) which is schematically represented in Fig. 4. The fabricated composites possess high specific strength and modulus, and stability as structural materials [20]. Moreover, they have several advantages over other materials such as metals, alloys, and ceramics, since they have low density, do not corrode, and have higher fatigue endurance. They are also electrically insulating, have a low coefficient of thermal expansion compared to metals, and enable reduced vibration and noise. Long-fibre laminates and fabrics are suitable for high-strength composites, whereas short/chopped fibre and particulate composites are used for moderate strength requirements. Table 1 shows that FR-PMCs can be manufactured by a variety of methods.

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Fig. 4 Classical classification of polymer matrix composites (PMCs) Table 1 Different fabrication processes for FR-PMCs [21] Technique

Characteristics

Applications

Sheet moulding

Fast, flexible, 1–2 // fibres

SMC automotive body panels

Injection moulding

Fast, high volume, very short fibres, thermoplastics

Gears, fan blades

Resin transfer moulding

Fast, complex parts, good control of fibre orientation

Automotive structural panels

Prepreg tape lay-up

Slow, laborious, reliable, expensive (speed improved by automation)

Aerospace structures

Pultrusion

Continuous, constant cross-section parts

I-beams, columns

Filament winding

Moderate speed, complex geometries, hollow parts

Aircraft fuselage, pipes, driveshafts

Thermal forming (future)

Reinforced thermoplastic matrices, fast, easy repair, joining

All of the above applications

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FR-PMCs are used in a variety of high-performance structural applications in aerospace, ground transportation, and civil infrastructures. Polymer composites reinforced with carbon fibres are used for aerospace applications, while glass fibre-reinforced composites are preferred for automobiles. Recent trends in composites research have focused on high temperature as well as toughened resin systems; high strain and hybrid fibres; fast and low-temperature curing systems; thermoplastics; and self-healing composites. (1)

(2)

(3)

Thermosetting Composites (TSCs) based on polyester resin, followed by vinyl ester and epoxy resins, are well established. Resins like bismaleimide, polyimide, and cyanate ester resins are also used for high temperature and high-tech applications. This article in this section presents a brief on a few instances of state-of-the-art research and development and applications of fibrereinforced polymer matrix composites, especially the thermoplastic composites (TPCs) and self-healing polymer-modified FRPMCs, apart from a brief note on their applications. Thermoplastic composites (TPCs) have become competitive candidates for replacing thermoset composites (TSCs) and metallic complex parts in aerospace applications. High-performance aerospace-grade polymers such as polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylsulfone (PPSU), and polyetherimide (PEI) provide a reliable and cost-effective way to reduce the weight of aerostructures. Airbus, for example, has used thermoplastic for a primary structural component in the door of the A350 XWB to improve quality and reduce weight and costs by 40%. PEEK pipes are used instead of metal pipes to protect high-voltage cables in commercial aircraft. In LCA-TEJAS, PEEK-based lightning insulator pipes are used in fuel lines to protect the aircraft from the lightning effect. The initial drives for the usage of thermoplastic composites were their good impact resistance (durability) and inherent flame resistance properties. They provide better damage tolerance than thermoset composites. Therefore, they are considered to be the future generation of structural materials for the aerospace and defence industries. Besides these applications, thermoplastic composites made with glass fibres (GF), carbon fibres (CF), and natural fibres (NF) have increasingly found their uses in the automotive and renewable energy sectors, owing to their properties like lightweight, construction potential, integral design, and good impact properties [22]. Thermoplastic Composites enable shorter production times, but need new fabrication techniques. An important additional point is that they can be recycled via a novel grinding process and/or melt processing. This is not possible for thermosetting composites. Fibre-reinforced Self-healing Polymer Composites By definition, selfhealing materials should have the capability to automatically heal the damages and/or microcracks that occurred during service conditions. Thus, fibrereinforced polymer composites having self-healing ability significantly will increase the longevity of materials and also cover the safety aspect of using

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Fig. 5 Design strategies of self-healing polymers/composites

the components and aerostructures. The design methodologies for self-healing polymeric materials and composite structures are primarily two types: intrinsic and extrinsic methods (Fig. 5). In the extrinsic method of self-healing, the healing precursors/agents are incorporated separately into the matrices and composite structures in the form of microballoons, hollow glass fibres, or microvascular systems. During crack propagations, once the healing reservoirs are broken and the healing agent filled the microcracks and get polymerized by the embedded catalysts in the composites. Thus, the crack is healed. On the other hand, in the intrinsic method the inherent functionality of polymer matrices allows automatic healing and no additional healing agents are needed. Polymer composites having both self-healing and morphing functionality have tremendous potential for fabrication of adaptive aerostructures in defence applications, the global market for unmanned air vehicles (UAVs) will be worth $55 billion by 2020–23. This nascent field of research is highly demanding and challenging as well [23].

1.5 CMCs Ceramic matrix composites (CMCs) are used for high-temperature applications beyond 700 °C. The CMCs can be further divided based on the nature of the matrix and based on the reinforcement type. Based on the matrix types, the CMCs are broadly categorized in oxide (silica, quartz, and alumina) and non-oxide ceramic matrices (SiC, Si3 N4 , ZrB2 , ZrC, BN, and TaC) composites [1, 2, 5]. Carbon fibres,

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SiC fibres, Alumina fibres, and Quartz fibres are the main ceramic reinforcements which are used for fabricating different types of CMCs in a combination of the abovementioned matrices. Continuous carbon fibre and Silicon carbide fibres have been used successfully for many aerospace applications while limited uses for quartz and alumina fibres are reported, e.g. quartz–silica composites are used for hightemperature electro-magnetic transparent windows and radome applications, and alumina–alumina composite are used for other high-temperature applications [5, 24–28]. Since machining of the CMCs is very difficult and requires special tooling, therefore CMCs have to be fabricated to the near-net shape of the final product. Therefore, ceramic fibre reinforcement requires special weaving techniques in order to make near-net preforms like 2D fabrics, integrally woven 3D preforms, and 4D woven and needle punch preforms. Conversion of the conventional fibre tows/yarns into the useful preforms is a complex and very challenging process. 3D orthogonal and 4D woven preforming process has already been developed in the country but needle punched 2.5D preforming process with the required fibre volume fraction is under the developing stage in the country. Continuous carbon fibre/carbon matrix composites (CFCCs or C/Cs) have been developed for high-temperature lightweight structural materials because of their unique properties, including thermal shock resistance, low density, high specific heat capacity, and non-brittle and quasi-ductile fracture behaviour [3, 5]. Typical applications are automobile and aircraft brake liners. The studies on CFCCs are many [3–5, 9–15] and some of those studies are discussed briefly in the later parts of this chapter.

1.6 FR-CMCs: C/SiCs and SiC/SiCs In order to improve the oxidation resistance of C/Cs, continuous carbon fibrereinforced silicon carbide matrix composites (C/SiC) have been developed, mainly for propulsion and erosive applications, as in rocket nozzles. The environment encountered by rocket nozzles and other parts like jet vanes is very severe, with typical exhaust gas temperatures around 2500 K, and hard particles of alumina in the exhaust gases result in severe erosion. Other applications include advanced aeroengine components and reusable hot structures. Polymer precursor-based processing is preferred for ease of manufacturing complex-shaped ceramic structures. Polycarbosilane (PCS) has been used for fabricating C/SiC and SiC/SiC composites using the standard resin transfer method, the filament winding process, and also the moulding method. The synthesis processes for polycarbosilane and SiC fibres have been studied by many researchers. Hightemperature application SiC fibres are prepared using radiation stabilization and by modifying the PCS with metal incorporation. C/SiC composites are fabricated via different routes like Liquid Silicon Infiltration (LSI), Chemical Vapour Infiltration (CVI), and Polymer Infiltration and Pyrolysis (PIP). The German Aerospace Centre (DLR) has developed LSI-based C/SiC

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composites, particularly for advanced braking systems and jet vanes. Jet vanes have also been developed by the Australian Defence Research and Development Organization (DSTO) using 3D-stitched preforms and the LSI process. CVI-based C/SiC composites are fabricated by depositing SiC from methyl-tri-chloro-silane vapour infiltration into carbon fibre preforms. The LSI process enables thicker and complex-shaped C/SiC products to be fabricated more easily than via the CVI and PIP processes. Fabrication of C/SiC composites using the LSI process can be categorized into two distinct steps: (i) fabrication of a porous C/C preform and (ii) infiltration of the preform with molten silicon under vacuum or an inert atmosphere. The impregnated silicon reacts with the carbon matrix of the C/C and results in the formation of C/SiC. This reaction takes place instantaneously, and the processing times to obtain C/SiCs are shorter than those for the CVD/CVI and PIP methods. However, a major disadvantage of the LSI method is the higher processing temperature, ranging 1450–1650 °C. Table 2 compares the typical properties of C/SiC composites. It is seen that CVD/CVI-processed C/SiCs offer superior mechanical properties compared to the LSI-processed composites [24]. However, different researchers have reported different ranges of properties for similarly processed C/SiC. The polymer impregnation pyrolysis (PIP) process has been adopted to fabricate large-size C/SiC composite products like thin-walled rocket nozzles, which reduce the overall weight of the propulsion system compared to C/Phenolic nozzle systems. Extensive studies are being carried out at DMSRDE to develop the PIP process for C/SiC. The PIP-based composites are fabricated by impregnating SiC precursors into multi-directional carbon fibre preforms, followed by curing and pyrolysis; see Fig. 6. The impregnation, curing, and pyrolysis steps have to be repeated several times to obtain the desired strength and density of the composites.

2 Structural Applications of FRCs: Present Status and Future Prospects 2.1 FR-PMCs The rapid growth of composite consumption is observed especially in the transportation sectors (aerospace, marine, railways, and other ground transportation) and the construction industries. Standard modulus (high-strength) FR-PMCs (carbon fibrebased epoxy composites) are widely used for many components in aircraft, satellites, antenna dishes, missiles, etc.; and high- and ultrahigh modulus composites are used in primary structural parts in high-performance fighters, aircraft, and space structures. FRCs using E-glass fibres are used for general purposes where strength and high electrical resistivity are required. These are also used for small and secondary aircraft parts, aircraft interiors, radomes, and rocket motor casings. S-glass fibre-reinforced composites are used where high strength, modulus, and stability are required in

4–7

W/m K

J/kg K

m/mo C ( )

m/mo C ( )

Thermal conductivity

Specific heat

CTE (×10–6 )

a Thermal

900 (100 °C)

11.53 (100 °C)

590

measured values, yet to be published diffusivity at RT-1200 °C in mm2 /s

* Laboratory

2–3

MPa

Compressive strength

0.3–1.1

%

1.0–1.5

−

−

5

3

800 (RT)

−

− −0.5–2.5

35-7a

5.5–6.0

30-35a

−

−

300–350

−

−

0.15–0.35

−

0.2–0.35

60

80–190

180–200

2.4

2D

LSI-based

0.2–0.4*

55–70

185–230

175–200*

300–350

350–450*

1.7–1.75

50–55

2D

454–720

1.82–1.90

52–55

UD

PIP-based

0.6–0.9

90 − 100

Strain to failure

300 − 380

Young’s modulus

60 − 80

MPa

GPa

Tensile strength

200 − 250

MPa

Flexural strength

2.1–2.2

42–47 450–500

1.7–1.8

Density

250–330

42–44

Vol.%

g/cm3

Fibre content (Vf )

2D

Property

3D

CVD/CVI-based

Units

Composite types

3.0–4.5

−0.5–1.5

750–900

50–15*

−

−0.5–0.9

−

37-8a

−

−

0.10 − 0.15

−1.2–1.5

−

40-6a

100–110

−

−

−

− −

100–120

2.2

36

4D woven

170–220

2.3–2.35

40–45

3D woven

−

70–90

140–180

2.1–2.2

40–45

3D stitched

Table 2 Typical properties of C/SiC composites [with different fibre architectures and fabricated by the CVD/CVI, PIP, and LSI processes] [24]

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Fig. 6 Schematic of the processing of PIP-based C/SiC composites [25]

extreme temperature and corrosive environments, e.g. in highly loaded parts in small passenger aircraft. Organic fibres such as aramid fibres (Kevlar) and ultrahigh molecular weight polyethylene fibres and fabrics (Dyneema and Spectra) are used in composites for specific applications such as radomes, rocket motor casings, ballistic protection, and some structural parts and highly loaded parts. In a typical high-performance aerostructure, more than 50% of the airframe is made of FR-PMCs, with the remaining being of 20% aluminium, 15% titanium, 10% steel, and 5% other materials. Boeing’s latest civil airliner, the 787 Dreamliner, uses composites for half of its airframe including the fuselage and wing. Carbon fibre–epoxy composite airframes are lighter and stronger by design. Polymer matrix composites are widely used in aircraft such as landing gear, hubcaps, radomes, manhole covers of fuel tanks, pylon fairings, leading edge, impeller blades, door handles, gears, and bearings. The co-cured technology, one of the most appropriate ones for PMCs, has been established for the carbon-BMI (bismaleimide is a hightemperature resin system) for many composite parts for Indian LCA-Tejas aircraft, for example, the fin assembly and centre fuselage components of LCA- Mk I (Fig. 7a).

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Fig. 7 LCA-FIN Co-cured Torsional Box (a) and Use of FR-PMC in the indigenously developed fighter aircraft (b) (Courtesy DRDO)

The Tejas aircraft in total contains 45% composites by weight and 90% by surface area (Fig. 7b). It is very difficult to estimate the accurate output of polymer matrix composites globally. However, it was reported that the world’s output was 3.9 million tons in 1990, of which are 1.503 million tons in the United States, 1.485 million tons in Western Europe, 0.643 million tons in Japan, and 0.106 million tons in China. In the United States, about 3 billion pounds of composite products are manufactured each year. There are approximately 2000 composite manufacturing plants and materials suppliers across the U.S. About 65% of all composites are produced with glass fibre and polyester or vinyl ester resin, and are manufactured using the open moulding method. The remaining 35% are produced with high volume manufacturing methods using carbon or aramid fibres. Moreover, the market of thermoset composites was valued at USD 41.98 Billion in 2016, and is projected to reach USD 57.98 Billion by 2021. The most widely used thermoset resins are epoxies in composite materials. These epoxy resins are enabling to tailor make by varying curing systems and reinforcements. Global Epoxy Composite Market is growing at the rate of 7.06% annually. In 2016, the global epoxy composite market was 21.04 USD Billion and forecast to reach 39.19 USD Billion in 2023.

2.2 CFCCs Owing to their unique combination of thermal and mechanical properties and density, C/SiC composites are used in numerous aerospace and defence applications. Also, there are some important applications in the high-temperature industries, where these composites are used at extreme temperatures up to 2500 °C for short durations, e.g. thrust vectoring controls and rocket propulsion systems. (1)

PIP-based C/SiC composites were initially developed mainly for space applications, like the thermal protection shields (TPSs) of reusable spacecraft. C/SiC composites are also preferred for hot gas liners in aero-engines and in rocket

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(2)

(3)

(4)

199

propulsion, owing to their excellent stability at high temperatures and their thermal shock absorption capability. Apart from high-temperature applications, these composites are also used for satellite structures requiring high precision and stringent dimensional stability. PIP-based C/SiC composites with ceramic coatings are being studied by the DMSRDE for use as dense radiation-cooled C/C-SiC nozzle demonstrators. Considering the gas tightness requirement of the nozzle, a match die moulding technique was adopted. This reduces the through-thickness pore channels. To obtain a testable nozzle, a moulding tool has been designed and developed. This tool has the unique feature of PID-controlled inbuilt heating giving a controlled heat input to the composite. The selected nozzle divergent cone is 450 mm long with a base diameter of 280 mm and a throat diameter of 120 mm (Fig. 8a). Four nozzle components have been fabricated to study the effect of density, resin composition, and fibre volume fraction (Vf ) on permeability and densification efficiency. Hot structures of the reusable hypersonic vehicle are required to be made of ceramic composites. According to the literature, C/SiC composites are considered suitable for these applications. The large C/SiC components required for the hot structures are difficult to fabricate using the other two conventional techniques, viz. LSI and CVI/CVD. Considering the futuristic requirement of the defence systems, a typical shape was chosen (Fig. 8b). The prototypes have been densified. LSI-processed C/C-SiC composites are mostly used for industrial applications and brake discs. Details of different applications are beyond the scope of this chapter, but here we give an example of the use of this processing technique for jet vanes. These are used for the thrust vectoring control of quick-action tactical missiles. The materials for jet vanes should be erosion-resistant (to particulate flow) in addition to thermal shock resistant (i.e. they need to have high thermal conductivity, low coefficient of thermal expansion (CTE), and high tensile strength. Also, (i) the materials have to be optimized to address the conflicting demands of high fracture toughness (high carbon content) and high

Fig. 8 PIP-based C/SiC nozzle prototypes (a) and 1/5th scale down second section of HSTDV cruise vehicle hot structure prototype (b) (Courtesy DRDO)

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Fig. 9 Typical images of Jet Vanes in a rocket motor. (Courtesy DRDO)

resistance to abrasion/erosion (high SiC content), and (ii) erosion of the jet vane depends on the fibre architecture, Vf , and testing/operation conditions. C/SiC jet vanes have been developed [26] using LSI-based 3D-stitched preforms, and have shown excellent resistance to the plume of a solid rocket motor (SRM). Figure 9 shows a typical jet-vane component. C/SiC thrusters have been qualified as part of an effort to develop the AESTUS C/SiC expansion nozzle. LSI-based 4D C/SiC nozzle throats and inserts having uniform thermo-mechanical properties have been tested with a mixed hydrazine/nitrogen tetroxide fuel [27]. The 4D C/SiC nozzle throat performed much better than conventionally used high-density graphite or C/C nozzle throats under similar testing conditions; see Fig. 10.

2.3 Thrust Research Area and Challenges in CFCMCs Though the country has made significant progress in the last two decades in fabricating C/C, CFCMCs, and CMC for different applications of Indian defence and space, there are several challenges which need to be addressed before achieving the near-future targets. The challenges in CMCs and CFCMCs can be classified as follows:

2.3.1

Basic Raw Material Manufacturing

Different grades of glass fibres are being produced in India at a commercial scale, and their subsequent processing like weaving and preforming has been developed successfully. T300 Carbon fibres are produced at NAL Bangalore in limited quantity, but their commercial-scale production is under development. All other hightemperature fibres including the high modulus carbon fibres are imported and the fibres like Silicon carbide and Alumina are not available to the country even from the import route. Silanes, polycarbosilane which are the raw materials for Silicon carbide matrix are also imported in nature. Raw materials for polymer-derived ceramics and

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Fig. 10 C/SiC throat inserts: a Test hardware mounted on the test rig, b test in progress, c tested graphite throat, and d tested 4D LSI-based C/SiC composite throat insert. (Courtesy DRDO)

ultrahigh temperature ceramics are not available from the local routes. Therefore, the Indian industries must take the challenge of producing the ceramic fibre reinforcement and matrix raw materials at a commercial scale to make the country self-reliant in this key area. However, the low volume requirement poses enormous pressure on the industries to manufacture these materials at a competitive cost. The manufacturing of continuous carbon and silicon carbide fibres can be initiated through public–private partnerships where technology can be developed through joint efforts of DRDO, ISRO, and BARC, whereas the production can be realized through governmentowned industries like BDL, MIDHANI, etc. C/C brake disc production for defence applications has been taken up by M/s Graphite India and such industries can be encouraged for other C/C and C/SiC composite product production also.

2.3.2

Realization of Process Facilities

Process facilities play a decisive role in the selection of the process type and achieving the required properties of CFCMCs and CMCs. The process facilities required for the high-end products based on C/C or for C/SiC, SiC/SiC, and UHTCs are very critical, and the large-size facilities like High-Temperature pressure Impregnation, Carbonization, Graphitization, Chemical Vapour Deposition, Vacuum Metal Infiltration, and Vacuum Hot Press are under embargo. Recently, Indian Industries have designed and fabricated large-size C/C composite process facilities: M/s Hind

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high vacuum—high-temperature vacuum furnaces, M/s Inductotherm—graphitization furnaces, and M/s IFI in building highly specialized process equipment like isostatic presses. However, some industries must take up the design and fabrication of reliable CVI furnaces (Iso thermal/thermal gradient/film boiling equipment).

2.3.3

Research Areas

Apart from the raw materials and facilities, there are numerous challenges in realizing the reliable and optimum CFCMCs for the hypersonic environments which can be taken up by the research institutes and academia. The main challenges which need to be taken up on priority are mentioned as follows: • • • • • • • •

Synthesis of precursors for ultrahigh temperature ceramics Preforming processes like needle punch preforming and woven preforming Efficient processes for C/C and CFCMCs Development of multi-layer oxidation coatings on C/C composites for extended durations under hypersonic environment Machining processes and non-destructive techniques for CFCMCs Generation of high-temperature property data of different CFCMCs for designers Bonding and joining of CFCMCs like C/SiC and SiC/SiC with their counterparts for reusable applications Residual life prediction of CFCMCs under a given application, etc.

3 Opportunities and Challenges in FRCs by the Advent of Nanotechnology A number of papers, reviews, patents, and books have been published in the last couple of years on the recent advances in the design and development of composite matrices with the introduction of nanomaterials [28]. It has been predicted that hybrid ‘tailor-made’ nanofillers-based FRCs possess all the characteristics to become the materials for the future. Manipulation of the macroscale properties of polymer, ceramic, and metal matrices by infusing nanoscale structural variables leads to enormous opportunities for technological and scientific understanding of nanocomposites; see Table 3. The interactions between matrix and nanomaterial surfaces lead to drastic changes in mechanical and electro-optical properties of FRCs. The diffusion of nanomaterials into the matrix to constitute an extended structure greatly affects the rheological, viscoelastic, and mechanical properties of the FR-nanocomposite, even at very low percolation thresholds. The fabrication methods of nanocomposites are compatible with the conventional polymer, ceramic, and metal matrix processing technologies, and therefore no costly lay-up alterations are required.

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Table 3 Inherited properties of hybrid nanomaterial-based composite materials and their possible applications [29] Hybrid nanomaterials and inherited properties in the composites

Applications of composites prepared using hybrid nanomaterials

Large surface-to-weight ratio

High effective energy, improved cycling performance, improved ion-transporting membranes for fuel cells, tailoring of the nano-architecture for thickness, lower density and porosity, higher surface area and conductivity, corrosion/wear-resistant tunable platform for controlling surface wetting

High strength and stiffness

High flux and low energy consumption filtration media for water and air, interleave materials for improved damage tolerance

Multifunctionality

Sensors having the ability to detect at lower concentrations of analytes, the coating having both electric and magnetic properties for effective shielding of electromagnetic waves, anti-counterfeiting of drugs, thermal interface materials, membrane for water purification, and smart textile

Lightweight with tunable electrical and thermal Aerospace components, microchips, housing conductivities for electronics, thermal management, sports and structural engineering applications

The distribution and orientation of nanomaterials in the matrix critically affect the synergistic properties of the composites. Large variations in physical and morphological features were reported due to the non-uniform dispersion of nanofillers for systems nominally of the same composition but prepared using different techniques. The geometry of fillers like particulate (0D), tubular/fibrous (1D), and sheet/plate (2D) dimensional nanomaterials also showed a large impact on the properties of FRnanocomposites [29]. Parameters like aspect ratio, higher accessibility of surface curvature, and the energetics of the low-dimensional nanofillers determine the wetting of the polymer matrix, which in turn influences the physical and mechanical properties of the nanocomposite. The next generation of FR composites will have engineered morphologies, and the introduction of carbon nanotubes (CNTs) or graphene into the matrix brings extra possibilities to cater to the desired properties. The high flexibility, low mass density, and large aspect ratio make CNTs unique as reinforcing fillers. The first CNT-based composite was reported within 3 years of the discovery of CNTs [30]. The axial elastic modules and tensile strength of single-walled carbon nanotubes (SWCNTs) were theoretically predicted and experimentally demonstrated to be as high as 1–2 TPa and 10–54 Gpa, respectively [30]. Although the physical and chemical properties of SWCNTs are much superior to non-walled CNTs, these have become the most widely used materials, particularly for composite applications, due to their relatively low production cost and availability in large quantities.

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The large surface area, high modulus, and strength of CNTs and graphene make them good candidates for reinforcing host matrices like resins, polymers, ceramics, and metals [31]. Numerous experiments have shown remarkable enhancement of mechanical strength with an addition of a small amount of CNTs or graphene. However, it was soon realized that there are still some manufacturing challenges to be addressed, owing to the poor interfacial interaction between nanotubes and the surrounding matrix [32]. The three critical issues for carbon nanomaterials-based composites are (i) the uniform dispersion of nanofillers in the host matrix, (ii) the proper interaction between the CNTs or graphene with the host matrix, and (iii) the alignment of nanofillers within the matrix [32]. Surface modification of nanomaterials by chemical functionalization helps avoid the problem of poor dispersion of nanofillers in the matrix. Generally, CNTs or graphene are chemically modified either by covalently attaching the functional group to the surface of nanomaterials, or by wrapping polar/nonpolar molecules onto the material by noncovalent interaction as illustrated in Fig. 11. The covalent functionalization of CNTs or graphene is very effective in enhancing the proper dispersion in the matrix, whereby the interaction of the attached functional groups on nanofillers with the host matrix is of utmost importance for achieving higher mechanical strengths. The judicious choice of a functional group for nanofillers is therefore very critical to achieving the optimum reinforcement effects in nanocomposites [32].

Fig. 11 Functionalization strategies for carbon nanotubes and graphene [30]

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Multi-scale FR-nanocomposites have unique combinations of two reinforcements at different size scales: fibres at the microscale and nanofillers at the nanoscale. The opportunities to tailor the physicochemical properties of the matrix by controlling the length (size) scales of the reinforcements provide a platform to modulate the stiffness, strength, and conducting properties of nanocomposites. FR-nanocomposites have been applied for retrofitting/strengthening beams, columns, and slabs of buildings and bridges. The most widely used composites have polymer matrix materials, which are lightweight but typically poor conductors. An important application of FR-PMC nanocomposites where electrical conductivity is in demand is for aircraft structures, to avoid damage by lightning strikes. At DMSRDE, conductive polymer composites are being investigated as possible replacements for non-conducting polymer matrix materials. This would eliminate the need for add-on metallic conductors, which are too heavy and may be difficult to repair. DMSRDE has developed a patented method to (i) synthesize hybrid hierarchical 3D carbonaceous nanostructures, (ii) introduce them into a polymer/resin matrix at an optimum weight percentage, and (iii) prepare a composite with carbon fibres as the reinforcement. The purpose is to investigate the conduction channels in and across the fibre orientations. The modulation (enhancement) of conductivities was obtained by reducing the thermal boundary resistance. The mechanical strength was also improved due to better interfacial interactions. A large enhancement in thermal conductivity is generally accompanied by increased electrical conductivity. The patented method reports that the rate of increase in thermal conductivity is much higher compared to the electrical conductivity. The design of materials to provide efficient thermal conduction channels in carbon fibre-reinforced composites gives the opportunity to use the entire structure for thermal management applications. Based on these material systems, a contemporary technique has been developed which enables indigenous fabrication of stateof-the-art torpedo propulsion technology, see Fig. 12, with advantages in terms of stealth, power density, and quality of torque. Lightweight fibre-reinforced nanocomposite materials with superior thermal transport properties should have an impact on the control of thermal management, and may be directly used for engineering,

Fig. 12 The propulsion motor parts a end covers, b rotors, and c stator core with copper windings developed using a base of FR-nanocomposite. (Courtesy DRDO)

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electronics, and structural applications [33]. A higher thermal conductivity is also important for cooling electronic circuits. Finally, we note that the use of nanomaterials as fillers in polymer, ceramic, and metal matrices provides an unprecedented opportunity to improve the damping in dynamic conditions with a bespoke formulation [34]. The Indian industries are witnessing a radical change by the advent of new technological advances where the contemporary fibre-reinforced composite manufacturing and production centres are now looking forward to many niche applications in strategic areas. The R&D institutes are actively pursuing research on nanoscience and technologies to transform the laboratory-scale understanding towards the industrial-scale production for service life and high performance. The optimized fibre-reinforced nanocomposite is lighter, shows improved strength and increased conductivity with retained original characteristics of FRC is now the pressing issue for future engineering materials. Aviation and defence are the two most diverse industries which have a history of public–private partnership, and in recent years a growing trend has been observed to develop nanocomposite materials with intended properties by hand-holding between academia and industry. Fibre-reinforced nanocomposites are considered to be of paramount importance for the future needs of the armed forces, navy, and air force [35].

4 Future Challenges and Concluding Remarks There are several technical challenges for researchers and academia in the area of fibre-reinforced composites. The thrust areas for research, development, and manufacturing have been focused around basic raw materials and characteristic morphologies of reinforcing agents, matrix materials, and manufacturing technologies including process machinery and lifecycle management of composites. The following are some of the identified research areas where lots of interests have been shown in recent years: • Fibre/matrix interfaces and microstructure studies • Generation of extensive property data under different environments; composite properties vary depending upon the process conditions and other parameters • Life assessment studies • Quality and reliability studies • Long-term corrosion studies • Smart, nanocomposites/self-healing composites, multifunctional composites, stealth composite structures, etc. • Synthesis of new and cost-effective resins, low-temperature curing resins, and natural fibre composites • Process and design simulations and generation of high-temperature property data for designers

Present Status and Future Indian Perspectives …

207

• Development of endurable adhesives for bonding composite structures and joining of high-temperature structures like C/SIC and SIC/SIC for reusable applications • Development of multi-layer oxidation coatings for extended durations • Opportunity to develop high-end manufacturing and processing equipment. The present chapter of this special monograph summarizes various fundamental aspects of composites, in which fibres are reinforced in Metal- (FR-MMCs), polymer(FR-PMCs), and ceramic- (FR-CMCs) matrices; their fabrication methodologies; and possible applications/life cycle enhancements. The energy dissipation processes in each of these 3 categories of composites are outlined establishing the fact that the relative contribution of each of the outlined energy dissipation processes to the overall toughening is maximum for CFCCs. In this vital area of advanced technologies materials (see Table 4 for relative merits and limitations), adequate care must be taken to refer to present-day structural designs and their limitations, in order to optimize the strategies for obtaining the advanced engineering solutions. Indian industries, such as RAP, Allen Reinforced Plastics, RR Composites, Kineco Composites, Tata Advanced Materials, and ERCON Composites made significant contributions in the area of polymer matrix composites. M/s Graphite India, Hind High Vacuum, Inductotherm, and IFI have been significantly contributing to the development of for carbon–carbon brake disc production and in the fabrication of highly specialized process equipment like isostatic presses, vacuum, and hightemperature furnaces. The windmill blades, railway coaches, and pultruded bridges have been successfully developed using carbon composite structures. Indian industries have also shown capabilities in the area of manufacturing composite process equipment, like CNC filament and tape winding machines, autoclaves, RTMs, Curing ovens, presses, pultrusion machinery, etc. With the increase in the need for air and surface transportation, construction industry, mobile homes, pre-fabricated structures, low-cost housing, and space and defence programs, there is a great potential for Indian researchers, academia, and industry on a wide range of areas related to fibre-reinforced composites, in terms of newer and eco-friendly materials, efficient process technologies and manufacturing techniques, and reusable and safe disposal of composites.

Features of different composite types

Feasibility Studies conducted

Feasibility

Cost and Feasibility to achieve in Timelines

6

7

8

10

–

+ +

=

–

–

–

–

+

+

+

+

+

+

−

= =

−

+ +

=

+

+

=

=

=

=

+

+

+

+

+

+

++

++

−

−

−

−

++

+

+

+

+

++

+

SF

+++

+++

–

–

–

–

+++

++

++

++

+

++

++

LF

+

+

=

=

=

=

+

=

=

=

=

+

+

P

CMCs

++

++

−

−

−

−

++

+

+

+

+

+

++

SF

+++

+++

–

–

–

–

+++

++

++

++

+

++

+++

LF

++++

++

++

++

++

++

++

++

++

FRCs

Nano

Legend Used: P—Particulate; SF—Short Fibre; LF—Long Fibre; –: Very Poor; -: Poor/Inadequate; = : Neither Poor nor Good as compared to the base materials; + : Good; + + : Very Good; + + + : Excellent; + + + + : Exceptional

Indian JVs and Collaborations

Long-term Defence Perspective and Applications in Major Defence Systems

9

C. International perspectives

Raw Materials Availability

5 −

+

=

Thermal Properties

B. Indian status/competence

4

=

=

=

(d) Total Fracture Energy Release Rate (Jc )

=

=

=

(c) Fracture Resistance Curve: (JR Vs. a)

−

=

=

(b) Elastic–Plastic JIc

=

=

=

3

Fracture Resistance (a) Linear Elastic KIc

Modulus (Elastic and Bulk)

2

+

Strength

1 +

P

−

PMCs LF

P

SF

MMCs

+

A. Mechanical properties

S. No

Table 4 Relative merits and limitations of different composites

208 N. E. Prasad et al.

Present Status and Future Indian Perspectives …

209

Acknowledgements The authors acknowledge with deep appreciation the National Initiative of Drs. Sanak Mishra, Indranil Manna, Debashish. Bhattacharjee, and Shantanu Chakrabarti of INAE to bring out this special volume on “Future Landscape of Structural Materials in India (FLSMI)”. They also would like to thank their colleagues in various DRDO labs especially DMSRDE, DMRL, NSTL, ASL, DRDL, RCI, GTRE, and Non-DRDO labs like CGCRI, NAL, and academic institutions like IITs—Kanpur, Kharagpur, BHU (Varanasi), and IISc., Bangalore for their long associations and voluble contributions in many National FRC Initiatives and Programmes, especially those of Prof. L M Manocha, the Former DRDO’s Raja Ramanna Fellow for DMSRDE, Kanpur. The authors are greatly indebted to Dr. R J H Wanhill, Emeritus Scientist of NLR, Amsterdam, the Netherlands, for his critical review of the contents and many valuable corrections. Finally, the funding and support of DRDO are duly acknowledged.

References 1. K.K. Chawla, Composite Materials: Science and Engineering, 3rd edn. (Springer-Verlag, New York, 2012) 2. L. Nicolais, M. Meo, E. Milella E (eds.), Composite Materials: A Vision for the Future, (Springer-Verlag, London, 2011) 3. A.G. Evans, Perspective on the development of high-toughness ceramics. J. Am. Ceram. Soc. 73187–73206 (1990) 4. W.J. Clegg, K. Kendall, N.M. Alfordm, T.W. Button, J.D. Brichall, A simple way to make tough ceramics. Nature 7, 455–457 (1990) 5. N. Eswara Prasad, R.J.H. Wanhill (eds.), Aerospace Materials and Material Technologies, vols. 1 & 2, (Springer Nature, Singapore, 2017). 6. G. Savage, Carbon-Carbon Composites (Chapman and Hall, London, UK, 1993) 7. D.Y. Yoo, J.J. Park, S.W. Kim, Fiber pull out behaviour of HPFRCC: Effects of matrix strength and fiber type. Compos. Struct. 174, 263–276 (2017) 8. D.B. Marshall, W.C. Oliver, Measurement of Interfacial Mechanical Properties in FiberReinforced Ceramic Composites. J Am Ceram Soc 70, 542–548 (1987) 9. N. Eswara Prasad, S. Kumari, SV Kamat, M. Vijayakumar, G. Malakondaiah, Fracture behaviour of 2D-weaved, silica–silica continuous fibre-reinforced, ceramic–matrix composites (CFCCs). Eng. Fract. Mech. 71, 2589–2605 (2004). 10. N. Eswara Prasad, K. Dashinamurthy, SV Kamat, M Vijaykumar, Trans Indian Inst Met. 58, 853 (2005) 11. S. Kumari, RD Lalitha Kala, NV Viswewara Rao, N Eswara Prasad, M. Vijayakumar, Trans Indian Inst Met 60, 65 (2007) 12. A.G. Paradhkar, N. Shanti Ravali, N. Eswara Prasad, Mechanical behaviour of 2D and 3D weaved SiC-matrix, carbon continuous-fibre-reinforced composites: part 1. Flexural strength under static loading conditions. Trans. Indian. Inst. Met. 70, 1245–1250 (2016). 13. A.G. Paradhkar, N. Shanti Ravali, N. Eswara Prasad, Mechanical behavior of 2D and 3D weaved SiC-matrix, carbon-continuous-fibre-reinforced composites: part 2. Fracture toughness under static loading conditions. Eng. Fract. Mech.182, 52–61 (2017). 14. X. Wang, J. Zhang, Z. Wang, S. Zhou, X. Sun, Effects of interphase properties in unidirectional fiber reinforced composite materials. Mater. Des. 32, 3486–3492 (2011) 15. A. Gloria, D. Ronca, T. Russo, UD Amora, M. Chierchia, RD. Santis, L. Nicolais, L. Ambrosio, Technical features and criteria in designing fiber-reinforced composite materials: from the aerospace and aeronautical field to biomedical applications. J. Appl. Biomaterials Biomech. 9, 151–163 (2011). 16. C.H. Hsueh, Interfacial debonding and fiber pull-out stresses of fiber-reinforced composites. Mater. Sci. Eng., A 123, 1–11 (1990)

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17. A. Mortensen, J. Llorca, Metal Matrix Composites. Annu. Rev. Mater. Res. 40, 243–270 (2010) 18. D.B. Miracle, Metal matrix composites – From science to technological significance. Compos. Sci. Technol. 65, 2526–2540 (2005). 19. K.S. Munir, P. Kingshott, C. Wen, Carbon Nanotube Reinforced Titanium Metal Matrix Composites Prepared by Powder Metallurgy-A Review. Crit. Rev. Solid State Mater. Sci. 40, 38–55 (2015) 20. R.M. Wang, S.R. Zheng, Y.P. Zheng, Polymer Matrix Composites and Technology (Woodhead Publishing Ltd., Cambridge, UK, 2012) 21. S.G. Advani, K.T. Hsiao, Manufacturing Techniques for Polymer Matrix Composites (PMCs) (Woodhead Publishing Ltd., Cambridge, UK, 2012) 22. M. Biron, Thermoplastics and Thermoplastic Composites, 3rd edn. (Elsevier Ltd., Oxford, UK, 2018) 23. M.Q. Zhang, M.Z. Rong, Self-healing Polymers and Polymer Composites. (John Wiley and Sons, 2011) 24. S. Kumar, K Chandra Shekar, B. Jana, LM. Manocha, N. Eswara Prasad, C/C and C/SiC composites for aerospace applications. in Aerospace Materials and Material Technologies, vol. 1, Aerospace Materials (Springer Nature, Singapore, 2017), pp. 343–369. 25. S. Kumar, M. Bablu, S. Janghela, MK Misra, R Mishra, A. Ranjan, N. Eswara Prasad, Factorial design, processing, characterization and microstructure analysis of PIP-based C/SiC composites. Bull. Mater. Sci. 41, 17 (2018). 26. S. Kumar, A. Kumar, K. Sampath, VV. Bhanu Prasad, JC. Chaudhary, AK. Gupta, G. Rohini Devi, Fabrication and erosion studies of C–SiC composite Jet Vanes in solid rocket motor exhaust. J. Eur. Ceram. Soc. 31, 2425–2431 (2011). 27. N. Eswara Prasad, A. Kumar, J. Subramanyam, Ceramic matrix composites (CMCs) for aerospace applications. in Aerospace Materials and Material Technologies, vol. 1, Aerospace Materials (Springer Nature, Singapore, 2017), pp. 371–389. 28. P.M. Ajayan, O. Stephan, C. Colliex, D. Trauth, Aligned carbon nanotube arrays formed by cutting a polymer resin–nanotube composite. Science 265, 1212–1214 (1994) 29. M. Vinyas, SJ Athul, D Harursampath, M Loja, TN Thoi, A comprehensive review on analysis of nanocomposites: from manufacturing to properties characterization. Mater. Res. Express 6, 092002 (2019). 30. G. Mittal, V. Dhand, K.Y. Rhee, S.J. Park, W.R. Lee, A review on carbon nanotubes and graphene as fillers in reinforced polymer nanocomposites. J. Ind. Eng. Chem. 21, 11–25 (2015) 31. J. Njuguna, K. Pielichowski, J.R. Alcock, Epoxy-Based Fibre Reinforced Nanocomposites. Adv. Eng. Mater. 9, 835–847 (2007) 32. D. Roy, N. Tiwari, K. Mukhopadhyay, A.K. Saxena, The effect of doubly modified carbon nanotube derivative on the microstructure of epoxy resin. Polymer 55, 583–593 (2014) 33. N. Tiwari, N. Agarwal, Debmalya Roy, K. Mukhopadhyay, N. Eswara Prasad, Tailor made conductivities of polymer matrix for thermal management: design and development of topologically controlled hierarchical nanostructures. Ind. Eng. Chem. Res. 56, 672–679 (2017). 34. P.M. Ajayan, Bulk metal and ceramics nanocomposites, in Nanocomposite Science and Technology, ed. by P.M. Ajayan, L.S. Schadler, P.V. Braun (Wiley VCH Verlag GmbH & Co., KGaA, 2003), pp. 01–75 35. N.K. Mahenderkar, T. Ram Prabhu, A. Kumar, Nanocomposites potential for aero applications. in Aerospace Materials and Material Technologies, vol. 1, Aerospace Materials (Springer Nature, Singapore, 2017), 391–411.

Structural and Functional Properties of Architectural Glass Himadri Sekhar Maiti

Abbreviations AIGMF CAGR CGCRI CSIR DAE DRDO FTO GPa HF IIT ISRO ITO kJ Low E-Coatings MPa PVB R&D TERI USA

All India Glass Manufacturers’ Federation Compound Annual Growth Rate Central Glass and Ceramic Research Institute Council of Scientific and Industrial Research Department of Atomic Energy Defence Research and Development Organization Fluorine doped Tin Oxide Giga Pascal Hydrofluoric Acid Indian Institute of Technology Indian Space Research Organization Indium doped Tin Oxide Kilo-Joule Low Emissivity Coating Mega Pascal Polyvinyl butyral Research and Development The Energy and Resource Institute United States of America

H. S. Maiti (B) CSIR-Central Glass and Ceramic Research Institute, Kolkata, India Government College of Engineering and Ceramic Technology, Kolkata, India © Indian National Academy of Engineering 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_9

211

212

H. S. Maiti

1 Introduction Most building materials are characterised by their high mechanical strength—either tensile or compressive; in general, they are opaque in character with the only exception of glass, which is transparent. This unique property of glass has been exploited over centuries in the construction of windows, for which the mechanical properties are relatively of less importance. In addition to transparency, glasses can be prepared in different colours and shades, which have added to their attractiveness as window material. In ancient Greek houses and Gothic churches, it was very common to construct the architectural windows using pieces of coloured glass supported by frames made of either wood, bronze or most commonly the soft and flexible lead ‘cames’. However, the window panes and facades of the modern buildings are much larger in size (several metres in length and breadth), which have been made possible due to tremendous advancement in the science and technology of glass manufacturing, enhancement in their mechanical strength and also the technology of glazing, making the buildings much more energy-efficient than ever before. In this article, we shall therefore examine all these different aspects of glass properties making them particularly suitable for the construction of modern buildings. Glass is a material of choice for many different applications and as a result, there are several important books, book chapters, reviews and dissertations on the chemistry, physical properties and applications. A few are listed under reference section [1–7].

2 A Few Important Aspects of Glass (1) (2) (3)

(4) (5)

(6)

(7) (8)

This unique group of materials is known to mankind since 5000 BC. However, their properties have been significantly improved over the ages. The basic ingredient of glass is silica (silicon dioxide), one of the most abundantly available constituents of the earth’s crust. They require a fairly high temperature (1000–1500 °C) for their preparation. Fabrication to different shapes is relatively simple due to their favourable viscosity vs temperature relationship. They have an aesthetic appeal due to their transparency, range of colours and hue. From the mechanical property point of view, they are quite strong and hard, but brittle. The broken pieces are very sharp and are therefore dangerous for the users. Currently, the glass sheets are being manufactured in very large sizes (3.2– 5.1 m in length and 2.25–3.5 m in breadth) and different thicknesses (3–19 mm) suitable for structural applications. Glass is waterproof and unlike steel, they do not rust. Many functional properties such as optical transmittance and thermal reflectivity may also be introduced in glass by modern processing techniques.

Structural and Functional Properties of Architectural Glass

213

3 Types of Glass There are several types of glass depending on (i) chemical composition (ii) shape and size (iii) manufacturing technique (iv) physical properties and (v) areas of application. Based on chemical composition, they can be classified into two major varieties: (i) Oxide (including phosphates) and (ii) Non-oxide glasses, e.g. chalcogenides, fluorides, etc. All glasses can be sub-divided into (i) coloured and (ii) clear varieties. The colour of a glass is controlled by the addition of different compounds of variable valance cations. Coloured sheet/plate glasses are also referred to as tinted glasses. Depending on the shape and size of the final product, they may be classified as (i) bottle glass (ii) flat (plate/sheet) glass (iii) art glass, etc. where the compositions may slightly differ. Originally, the flat glasses were manufactured by drawing the molten (viscous) glass through a set of horizontal or vertical rolls. The latter process is known as ‘Fourcault’ process (See Fig. 1). However, this process is no longer in vogue. Instead, it has been replaced by the ‘Float Process’ (Fig. 2) in which the molten glass is allowed to float on a bath of molten tin, which ensures highly flat and wrinklefree surface of the glass sheets. The technique also ensures a nearly flaw-less surface leading to enhanced strength and thereby opening up the possibility of their application as large facades, windows and partition walls (structural members) of modern buildings. Glasses are further strengthened by different techniques. ‘Toughening’ is Fig. 1 Schematic of the ‘Fourcault’ process [8]

Rollers

A ceramic fixture known as ‘Debiteuse’’ Glass Melt

214

H. S. Maiti

Fig. 2 Typical layout of a ‘Float Glass’ plant [9]

one such technique in which a compressive stress is generated on the outer surfaces of the glass sheets so that the critical stress needed to initiate a crack (for fracture) increases significantly. There are two ways to toughen the glass sheets: physical and chemical. There is another way to strengthen the glass sheets by fabricating layered composites in which a thin and transparent layer of polymer (Polyvinyl butyral— PVB) is sandwiched between two layers of glass. An older version of reinforced glass is ‘wired glass’ in which a steel wire net is sandwiched between the two layers of sheet glass (Fig. 3a). Another variety of glass product is ‘glass bricks’ which are double-walled hollow brick-like shapes used in decorative partition walls of the old palaces and in some of the modern buildings (Fig. 3b). Figure 4 summarises all the different uses of architectural glass.

(a)

Fig. 3 a Wired glass [10]; b Glass bricks [6]

(b)

Structural and Functional Properties of Architectural Glass

215

GLASSES IN ARCHITECTURE

Load Bearing Elements

Beams & Floors (Tempered & Laminated Glass)

Facades

Building Fenestraons

Cladded Facades

(Windows/ Sliding Doors)

(Structural Glazing)

Staircases

Parons/ Walls (Glass Bricks)

Canopies/ Skylights/Roofs

Fig. 4 Summary of architectural uses of glass. Adapted from Ref. [6]

4 Mechanical Properties of Glass Glasses are characterised by their high Young’s modulus and hardness but they are, in general, brittle in character and therefore may lead to catastrophic failure. However, they can be toughened to a significant extent by either physical or chemical treatment. In addition, their strength can be further improved by lamination with intermediate layer(s) of a specific type of polymer. Detailed discussion on the various aspects of mechanical property is available in books, review papers as well as web-lectures [11–14].

4.1 Theoretical Strength of Glass One can calculate the theoretical strength of glass from the fundamental concept of bond strength at the molecular level. Primary bond in a silicate glass is obviously Si–O with bond energy of 435 kJ/mole (approx.) [14]. The best way to theoretically calculate the strength of a solid (in this case, glass) is to consider the variation of potential energy and interatomic force with interatomic distance in a two-body system, based on which the theoretical strength of a solid (in this case glass) may be expressed as [13]:  σth =

Eγ ao

1/ 2 (1)

216

H. S. Maiti

where σth is the theoretical strength of the solid, E is the elastic modulus, γ is the surface energy and ao is the equilibrium interatomic spacing under unstrained condition. In case of a brittle solid like glass, E is of the order of 70 GPa, γ is around 3.5 J/m2 and ao is of the order of 0.2 nm and therefore σ th is of the order of 35 GPa. However, in practice the strength value of silicate glasses has been found to be in the range of 70 MPa, which are around three orders of magnitude lower than the theoretical prediction. This has been explained considering the presence of microcracks (known as Griffith Flaws) which are invariably present on the surface of glass products, prepared under normal process of cooling from a high temperature.

4.2 Griffith’s Analysis Based on Inglis’ stress concentration approach [15] (As quoted in Ref. [13]), Griffith in 1921 [16] suggested that the observed low strength of glass is due to the presence of surface cracks larger than a critical length of c* and considering an energy balance approach, he derived the fracture stress (σf ) of a glass plate loaded in tension as follows:  1/2 σ f = 2γ f /π c∗

(2)

where γ f is the energy of the fractured surfaces and the equation is popularly known as Griffith equation. Glass being a brittle material, catastrophic failure occurs only when any of the existing cracks are larger than the critical length of c* . The probability of finding such a crack depends on the chemical composition (and therefore the exact bond energy) and also the shape and size of the glass surface. Approximate strengths of different silicate glass products are presented in Table 1, in which it may be noted that glass rods and fibres possess less surface area (not specific surface area) and therefore there is less probability of finding a supercritical crack and the observed higher strength. Table 1 Typical strength of different glass products

Sl. no.

Product type

Strength in MPa

1

Glass plate/sheet/bottle

14–70

2

Freshly drawn glass rod

70–140

3

Abraded glass rod

14–35

4

Freshly drawn glass fibre

700–2100

5

Handled glass fibre

350–700

Adapted from Ref. [3]

Structural and Functional Properties of Architectural Glass

217

4.3 Strengthening of Glass There are several methods to strengthen glass products (See Fig. 5). As discussed earlier, presence of fine cracks (Griffith flaws) is primarily responsible for mechanical failure of glass products. Therefore, one of the simple ways to strengthen glass is to remove these flaws either completely or blunt the crack tips by one of the three techniques, viz., (i) chemical etching with dilute HF, (ii) mechanical polishing, (iii) laser polishing. Other techniques to strengthen glass products include generation of surface compressive stress either by physical toughening or chemical toughening (ion exchange), lamination and wire-net reinforcement.

4.3.1

Removal of Surface Defects

In addition to the techniques of removing the surface defects mentioned above, changes in the technique of manufacturing the glass sheet have a significant effect on the strength of the sheets. For example, ‘Float Glass Technology’ (Fig. 2) in which the molten glass is allowed to float on a bath of molten tin (metal) produces a much better quality of glass sheets not only with minimum of surface ripples but also with less of surface defects. The technology also leads to a much higher production rate and therefore a lower cost of production. This stands in contrast with the previously practised ‘Fourcault Process’ (Fig. 1), which was in vogue for several decades. The glass sheets produced by the ‘Float’ process possess two types of surfaces. The lower surface is in contact with the tin bath, whereas the upper surface is exposed to air. Concentration of surface flaws varies slightly between these two surfaces (See Fig. 6). It may be noted that the density of surface flaws in glass plates is much less in case of ‘Float Glass’ compared to that in conventionally manufactured (‘Fourcault Process’) plates. Consequently, the strength is also significantly high in Float Glass. This improvement in mechanical property has led to widespread use of glass plate (manufactured by ‘Float Glass technology’) as one of the preferred structural components in modern buildings. In addition to their improved mechnical strength, they also

Chemical Etching

Mechanical Polishing

Laser Polishing

Surface Compressive Stress Physical Toughening (Quenching)

Chemical Toughening (Ion Exchange)

Fig. 5 Different techniques for strengthening glass products. Adapted from Ref. [17]

Wire net Reinforced

Removal of Surface Defects

Lamination

STRENGTHENING OF GLASS

H. S. Maiti

Fig. 6 Density of surface flaws on glass plates prepared by different technologies. Adapted from Ref. [18]

Number of Surface Defects /mm2

218

Polished plate glass prepared by convenonal process

150

100 Tin side of Float Glass Air side of Float Glass

50

0

0

400

800

1200

Strength (MPa)

perform other functions like light transmission and /or reflection as per requirement. This aspect will be discussed in detail later in this article.

4.3.2

Physical/Thermal Toughening (Tempering)

This is one of the most common techniques of strengthening glass products, particularly the glass sheets and plates. For this, the glass sheets are heated to just below the glass transition temperature (600–650 °C), followed by air quenching, i.e. fast cooling by a set of air jets; occasionally a liquid jet is also used. This sudden change in temperature (also known as tempering) leads to a non-equilibrium situation, as a result of which the surface cools much faster than the inner region (core). The surface does not get enough time to lower its specific volume, while the inner region gets little more time to do so. This results in the generation of a compressive stress near the surface and a tensile stress in the inner region. The situation may be graphically represented as in Fig. 7. The surface compressive stress partly neutralises the tensile stress required for the growth of the surface flaws resulting in overall increase of the fracture strength. It may be mentioned here that most of the architectural glass used in modern buildings are physically toughened glass plates. Figure 8 shows the typical layout of an automatic glass toughening plant.

Structural and Functional Properties of Architectural Glass

219

~ t/5

Thickness

~ t/5

0 Compressive Stress

Tensile Stress

Fig. 7 Schematic stress distribution pattern in a physically toughened glass plate

Quenching >620oC to RT

Cleaning Pretreatment - drilling -cutting -chamfering

Heating > 620oC Tempered Glass

Fig. 8 Schematic layout of an automatic glass toughening (tempering) plant. Adapted from Ref. [19]

4.3.3

Chemical Toughening

From the chemical composition point of view, most glasses are known as ‘Soda-limesilica’ glass, which indicates the major constituents to be Na2 O (soda), CaO (lime) and SiO2 (silica). One of the important characteristics of these glasses is the ‘ion exchange’ property, meaning that the alkali (Na+ ) present in the glass composition can easily be exchanged with other alkali ions, e.g. K+ or Li+ , which incidentally have ionic sizes different from that of Na+ ion. Such difference in ionic size introduces an internal stress, which may be either compressive or tensile, depending on whether the substituted ion (in this case Na+ ) possesses lower or higher size compared to the substituting ion. This phenomenon of ion exchange is the basis of chemical toughening. As in the case of the physical toughening, in this case also, a surface compressive stress is generated by exchanging a part of the surface Na+ ions by K+

220

H. S. Maiti

Aer ion exchange

MOLTEN SALT

Before ion exchange

GLASS

Fig. 9 Schematic representation of the ‘Ion Exchange Process’. Adapted from Ref. [20]

ions having ionic diameter larger than the Na+ ions. A pictorial representation of this situation is presented in Fig. 9. In practice, glass plates are immersed in a hot bath of potassium nitrate (KNO3 ) when K+ ions from the bath enter the glass structure while in turn the Na+ ions enter the bath. As it is controlled by a diffusion process, only a fraction of the thickness of the glass sheet takes part in this exchange process. The structure deep inside the sheet remains unaffected. Thickness on the exchange layer obviously depends on the temperature and the time of immersion. Typical bath temperature is ~475 °C. The thickness of the exchanged layer is 25–30μ if the time of immersion is around 16 h. [19]. As mentioned earlier, the exchange process generates a compressive stress on the surface and thereby enhances the strength of the glass sheets as in the case of physically toughened glasses. It may be noted that chemical toughening is costlier than physical toughening and is carried out only for very thin sheets for which physical toughening is impractical. Currently, chemical toughening is used extensively for mobile display glasses (the so called ‘Gorrila Glass’ patented by Corning Inc., USA) and flexible glass sheets (‘Willow Glass’ once again patented by Corning Inc., USA) proposed to be used for role-to-role micro-electronic device fabrication.

4.3.4

Lamination

This is another important and widely used technique for strengthening glass sheets/ plates based on the principle of sandwiched composite structure, in which two or more glass sheets are warm-pressed with an interlayer(s) of polymer acting as a bond between the glass layers. The particular polymer used is Polyvinyl butyral (PVB), which is thermoplastic in character by nature. The glass sheets may be annealed but more often they are tempered. The pressing is done in two steps: initially at a low pressure and temperature (0.5–0.8 bar and 80–100 °C) primarily to remove the air bubbles from the interlayer and finally autoclaved at a temperature of 135–145 °C and a pressure of around 12 bar [21]. The PVB is an ideal polymer for the purpose

Structural and Functional Properties of Architectural Glass

221

due to its excellent adhesive property and the close proximity of its refractive index to that of glass. The latter property ensures no loss of transparency of the laminated composite. The most important applications of this glass are in the automobile sector, aircrafts, armoured vehicles and railways, particularly in windshield and windows. They are also used in large size windows of the shopping malls to prevent vandalism. They are commonly referred to as ‘Saftey Glasses’.

4.3.5

Comparison of Strength

Strength values typically attainable with a few of the strengthening techniques are listed in Table 2. Table 2 Typical strength values of glasses strengthened by different techniques Sl. no

Strengthening method

Bending strength (MPa)

1

Raw glass (Annealed)

30–250

2

Toughened glass (Air quenched)

120–180

3

Toughened glass (Liquid quenched)

200–400

4

Chemically toughened (Ion Exchanged) Glass

450–800

5

Surface etched Glass (Please refer to Table 1)

1000–1700

Adapted from Ref. [17]

Specific Sffness (MNm/kg)

28. 27.

Glass- Physically Toughened

Glass – Chemically Toughened

27. Annealed Glass

26.

Aluminium Alloy (2014-T6)

26.

Aluminium Alloy 1100-H14 1% C Steel; Hot Rolled

25.

Low Carbon Steel

25.

0.

50

15 10 20 Specific Strength (kNm/kg)

25

30

Fig. 10 Strength/stiffness of toughened glass in comparison to steel and aluminium. Adapted from Ref. [14]

222

H. S. Maiti

Glass as a building material is used in association with steel and other metallic materials. Figure 10 provides a comparison of their strengths. For obvious reasons, the specific stiffness of glass is way above that of steel and aluminium alloys.

4.3.6

(1)

(2)

(3)

(4)

Important Properties and Applications of Tempered/Toughened Glass Tempered glass is 4–5 times stronger than annealed glass. Fortunately, this tempering process does not alter any other properties of the glass, particularly the optical properties. Toughened glass, being stronger, is difficult to break and even if it breaks due to impact, it shatters into small blunt pieces (Fig. 11) which do not cause serious injuries. Toughened glass cannot be cut or re-sized. Thus, the glass should be cut to the desired size and shape before the process of tempering. It is used in commercial applications where wind, snow or thermal loads are high, which cannot be handled by normal annealed glass; many countries have therefore scheduled the use of toughened glass in high rise buildings. Toughened glass can be combined with lamination to be used in windshields and windows of commercial automobiles, sports cars, aircraft, and railways. The fracture pattern of such glass is different from that of the toughened glass (Fig. 12) where broken pieces do not get separated due to the bonding action of the polymeric interlayer. Combination of toughened and tinted glass, toughened and laminated glass, toughened and insulated glass units are used in various sections of high-rise buildings, e.g. escalator side panels, handrails, even glass floors, roofs, skylight glazing, curtain walls, etc.

Fig. 11 Fragmentation of a tempered glass [22]

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Fig. 12 Fracture behaviour of laminated glass [23]

(5)

Several layers (up to 20) of toughened glass are laminated to make bulletproof glass. It is used in places having national security issues and also for personal protection.

5 Energy Efficient Glass Windows One of the primary considerations for the modern buildings is their energy efficiency. In other words, they are designed to be ‘Green Buildings’ for which their energy consumption is to be minimised. For this purpose, in addition to their architectural design, the optical property of the glass windows and facades play a very important role. As glass is transparent, most of the optical radiation passes through the glass sheet. However, a certain amount gets reflected depending on the surface characteristics of the glass. Emissivity is a material parameter and is defined as the ratio of heat emitted by a material to that by a blackbody, whose emittance is maximum and is taken as 1 (one). All other materials possess emittance of less than one; in fact, the complete scale is zero to one. In terms of percentage, a black body has an emissivity of 100% and for a perfect reflector the emissivity would be zero. Typical emissivity values of a few materials (main building materials together with a couple of highly conducting metals) are listed in Table 3. It may be noted that the emittance value of normal glass sheet is around 0.91, meaning ~ 91% of the incident thermal energy (primarily IR radiation) is transmitted; only ~ 9% is reflected back. However, for a low-E glass surface, one can have an emittance value as low as 0.04, i.e. only 4% of the incident heat energy is transmitted, rest 96% being reflected. For converting a normal glass sheet to a low-E one, one has to adopt a thin film coating technique (e.g. Magneton Sputtering, Spray

224 Table 3 Emissivity values of a few important materials.

H. S. Maiti Materials

Thermal emissivity (approx.)

Red brick

0.90

Concrete (rough surface)

0.91

Limestone

0.92

Marble (smooth)

0.56

Plaster (rough)

0.89

Glass plate

0.91

Aluminium foil

0.03

Silver foil (polished)

0.02

Adapted from Ref. [24]

Pyrolysis and Chemical Vapour Deposition) normally in continuation with the float glass manufacturing line.

5.1 Low-E Coatings Multi-layered thin film deposition technique is used to provide low-E coatings on glass sheets. This principle has been in use for more than a century. Significant development in terms of materials, deposition technique and design of the multilayer film has taken place during this period. Currently, 90% of the commercial glasses use silver (Ag) film as the primary working material supported by a number of other films of different materials which are needed either to protect or control the morphology of the deposited silver film. The typical structure of a multi-layer film assembly of a multilayer film containing two active silver layers is schematically presented in Fig. 15. In addition to this double silver layer coating, one can use either single silver layer or even a three silver layer coating depending on the required characteristics and area of application (Fig. 13). As this figure shows, in addition to the active silver layer, there are several other layers of different materials having different functions. The base layer of zinc stannate is used primarily to improve the adherence of silver layer to glass. Emissivity property, which in turn depends on the electrical resistivity of silver layer, is controlled by its grain size and grain orientation. Zinc oxide seed layer is required to control the morphology of the silver film. One also needs a blocker layer of titanium metal to protect the silver layer from the reactive plasma, which is used for the deposition of the next layer. An interlayer also of zinc oxide is required to separate two sets of layers separating the silver double layers. Finally, a top layer of titanium dioxide is deposited which protects the complete film from atmospheric contamination. Typical transmittance and reflectance spectra of a silver double-layer coated glass surface are presented in Fig. 14. Effectiveness of the IR reflection without changing the transmittance in the visible region is clearly demonstrated in this figure. One may note

Structural and Functional Properties of Architectural Glass Fig. 13 Typical multilayer stack of silver containing emissivity coating (Double layer silver). Adapted from Ref. [24]

225

Top Layer (Titanium Dioxide) Blocker Layer (Titanium) Silver Seed Layer (Zinc Oxide) Base Layer (Zinc Stannate) Interlayer (Zinc Oxide)

~ 150nm

Blocker Layer (Titanium) Silver Seed Layer (Zinc Oxide) Base Layer (Zinc Stannate) Glass

% Transmittance/ Reflectance

100

Reflectance  coating side 80

Reflectance  glass side

60

40

20

Transmittance 0 300

1300

800

1800

2300

Wavelength (nm) Fig. 14 Typical transmittance and reflectance spectra of coated and uncoated glass surfaces. Adapted from Ref. [24]

that the reflectance for the coated side in the IR region is significantly large than that of the uncoated surface. Electrical conductivity is one of the major parameters for controlling the emittance of the film. The relationship can be expressed as  =

8ε o ω σ

(3)

226

H. S. Maiti

IG Unit IG Unit Outboard Laminaon Inboard/ Outboard Laminaon

(e)

1 23 4

3 45 6 Interior

Exterior

1 2

(f)

5 67 8

Interior

5 6

Interior

Exterior

1 23 4

(d)

(c)

(b)

IG Unit Inboard Laminaon

1 23 4

5 6

Interior

Interior

(a)

3 4

Interior

1 2

Laminated Glass

Exterior

3 4

Exterior

Interior

1 2

Triple-Glazed Window Unit

Exterior

2

Exterior

1

Double-Glazed Window Unit

Exterior

Single layer Glass

(g)

Fig. 15 Various types of window configurations used in building construction. Different surfaces of the glass sheets are designated by the numbers starting from exterior to interior. Adapted from Ref. [25]

where  is the emissivity, εo is dielectric permittivity of the free space, ω is the frequency of the incident radiation and σ is the electrical conductivity. As the equation shows, the higher is the conductivity, lower is the emissivity. This is one of the considerations for choosing metallic silver as one of the preferred coating materials. In addition, some of the semiconducting materials like ITO (Indium-doped tin oxide) and FTO (Fluorine-doped tin oxide) have been tried with limited success. However, they are preferred from the cost consideration.

5.2 Window Design In a building, windows and the glass facades are the primary source of energy transmissiom between outside and inside. Particularly in a cold country, where insulation from outside cold is of prime importance, one uses either double-glazed or trippleglazed windows. In this case, the ‘Glazing’ refers to the individual glass sheets or window panes unlike applying a glassy coating as in the case of glazing a ceramic product. For double glazing, one would have two parallel glass sheets fixed in a

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wood, aluminium or polymer frame with an air gap in between. Similarly, for tripple glazing, there are three parallel glass sheets with two layers of air gap. In addition, one may use laminated glass sheets instead of monolithic sheets. All these different configurations are shown in Fig. 15. In the context of energy-efficient buildings, Low-E windows are of great importance. In the context of windows, low-E refers to a window system which transmits only a small fraction of thermal energy incident on it, the major portion being reflected back. Following are a few parameters to describe the property of the double glazed low-E windows: (1) (2)

(3)

U-factor: This is a measure of the heat loss that the window allows. Solar Heat Gain Coefficient (SHGC): This is the fraction of solar radiation admitted through the window, either directly transmitted and adsorbed or radiated inward. Visible Light Transmittance (VT): It is the measure of the amount of visible light passing through the window.

Examples of three different solar heat gain situations with different values of U-factors, SHGC and VT for a double glazed window are presented in Fig. 16. As the function of a window in a cold country where the heat is to be contained within the room (interior) is different from that in a hot country where the solar heat is to be reflected back (exterior), the window configurations are required to be different (Fig. 17). Actual design of a double glazed-window system is presented in Fig. 18 in which there are two glass sheets fixed in an aluminium frame with an air gap (occasionally filled with argon for better insulation) of around 20 mm. U Factor = ~0.26

Infrared

U factor =~ 0.25

U Factor = ~0.24

SHGC=~0.67

SHGC=~0.42

~67% of solar heat is transmied

~42% of solar heat is transmied

SHGC=~0.26 ~26% of solar heat is transmied

= ~0.72 ~0.78 ~78% of visible of light is transmied

VT = ~0.64

~72% of visible light is transmied

~64% of visible light is transmied

Visible

(a) High Gain

(b) Medium Gain

(c) Low Gain

Fig. 16 Pictorial representation of heat gain situation of a double glazed window with three different values of SHGC: a High gain; b Medium gain and c Low gain. Adapted from Ref. [26]

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H. S. Maiti

Exterior

Hot Weather Interior

Exterior

Interior

Cold Weather

Solar Heat

Visible Light

Fig. 17 The directions of heat reflection are different in cold and hot weather countries. Adapted from Ref. [27]

Fig. 18 Design of a double glazed window system with Low-E glass panes [28]

Out of the four glass surfaces, one of the two internal surfaces (facing the air gap) is coated with low-emissivity coating depending on whether it is used in a cold o hot country. In case of cold country, the surface ‘b’ is coated, whereas for the hot country, the coating is applied on surface ‘c’. It is to be noted that the glass on the left faces the exterior surface of the building and that on the right faces the interior of the building.

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6 Concluding Remarks Introduction of float glass technology led to production of large size glass sheets with improved mechanical and optical properties making way for the large-scale use of glass as an important building material. Toughening and lamination have improved the mechanical properties further without deteriorating the optical property. All countries around the world, including India, make extensive use of glass particularly in high-rise buildings. Glass with low-E coating forms an essential component of energy-efficient green buildings. Low-E coatings are not so important for rural housing particularly in this country due to relatively less use of air-conditioning. However, toughened and laminated glasses are useful to avoid vandalism. The estimated demand for low-E glass in this country is expected to increase at a CAGR of 25% during the period 2019–2025. Over this period the actual market is expected to reach US$ 1.7 billion by 2025, increasing from US$432 million in 2019 [29]. There are several multinational glass companies having their float glass production lines in India. Many of them also have their production lines for low-E coated and laminated glass sheets. Important ones are (i) Asahi India Glass Ltd., which is an Indo-Japanese company, having their manufacturing plant at Roorkee operating since 1984. (ii) Gujarat Guardian Ltd., a joint venture between Modi Rubber of India and Guardian Industries Ltd of USA. The company established in 1993 have their manufacturing plant at Ankleshwar, Gujarat and market their products with a brand name ‘Modiguard’. (iii) Saint Gobain India Pvt. Ltd. established in 1996 is a subsidiary of Saint Gobain S.A of France. They are the largest producer of float glass in India having their manufacturing plants at Sriperumbudur, Tamilnadu (Two float glass lines and a sputtering line for various types of coatings) and also in Gujarat. (iv) In addition, there are companies of Indian origin, e.g. Hng Float Glass Ltd promoted by Hindusthan National Glass & Industries Ltd. The company was established in 2006 with a plant at Halol, Gujarat. (v) Gold Plus Glass is another manufacturer which started functioning in 2009 with a turnkey project completed by a Chinese company Qinhuangdao Yaohua Glass Machine Manufacture Co Ltd. Considering the increasing demand for architectural glass in this country; both Saint Gobain and Asahi Glass have enhanced their manufacturing capacity by establishing new plants in recent years. The former has established its fourth plant at Bhiwandi, Rajasthan, which is operational since 2015 and the latter has started an integrated plant at Taloja, near Mumbai during 2017. Approximate installed capacities and capacity utilisation of these companies are given in Table 4. All the overseas manufacturers do have their strong corporate R&D activity, in their respective countries. The only exception is Saint-Gobain Research India (SGR India) set up by Saint Gobain Glass at the Research Park of IIT, Madras [34]. This is one of the company’s eight transversal global research centres to develop products, systems and solutions particularly for their own products. Unfortunately, there is no R&D activity in India particularly on architectural glass in the public sector. The only major R&D centre in India in the area of glass is CSIR—Central Glass

230

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Table 4 Installed capacity and utilisation factor of float glass plants in India [30–33] Sl. no

Company

Installed capacity (tonnes/day)

Capacity utilisation (%)

1

Saint Gobain India (4 plants)

2950

80–85

2

Ashai India Glass Ltd. (3 plants)

1750

80–85

3

Gujarat Guardian (Single plant)

650

90–95

4

Hng Float Glass Ltd (Single plant)

600

75–80

5

Gold Plus Float Glass Industry Ltd (Single plant)

450

80–85

TOTAL

6400

and Ceramic Research Institute at Kolkata, which specialises in strategic glasses required by DRDO, DAE and ISRO. Their activity in the area of commercial glasses is negligible. Considering the growing commercial importance and demand of this category of glass it may be worthwhile to set-up either an independent R&D centre in association with the All India Glass Manufacturers’ Federation (AIGMF) or as a part of CSIR-CGCRI particularly for the development of architectural glasses. There are many different aspects to be investigated in the areas of basic research particularly the design of the multilayer low-E coatings and their cost-effective techniques of application on the glass surface, e.g. sol–gel coating technique. Another important topic would be the development of silver-free low-emissivity coatings based on ITO and FTO. There is also a huge scope of redesigning the windows and facades in order to enhance the energy efficiency of the buildings.

References 1. A. Paul, Chemistry of Glasses (Chapman and Hall, London and New York, 1982) 2. B. Shand Errol, W.H. Armistead, Glass Engineering Hand Book (Literary Licensing, LLC, 2012) 3. K. Varsneya Arun, C. Mauro John, Fundamentals of Inorganic Glasses (Elsevier, Netharlands, UK and USA, 2019) 4. M.J. David, H. Juejum, C. Laurent (eds.), Springer Handbook of Glass (Springer Nature, Switzerland AG, 2019) 5. Wikipedia, Glass. https://en.m.wikipedia.org/wik 6. Wikipedia, Architectural Glass. https://en.m.wikipedia.org/wiki/Architectural_glass 7. R. Kennedy, Proceedings on Glass Processing days (1997) 8. Wikipedia. https://upload.wikimedia.org/wikipedia/commons/c/c4/Fourcault_process_for_ flat_glass_forming.svg 9. Course Material for Continuing Education Program of Vitro Architectural Glass: Understanding Low-E Coatings- PPT presentation. www.vitrowindowglass.com/lowe_glass/low-ewindows.aspx

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10. GharPedi, Characteristics & Properties of Glass as a Building Material. https://gharpedia. com/b 11. R. Bruckner, Mechanical Properties of Glass (Wiley Online Library, 2006), pp. 665–713. https://doi.org/10.1002/9783527603978.mst0102 12. B. Sugarman, J. Mater. Sci. 2, 275–283 (1967) 13. Web Lecture of Lehigh University, Mechanical Properties of Glass (2008). https://www.leh igh.edu 14. R. Lehman, The Mechanical Properties of Glass (Web Lecture of Rutgers University). http:// glassproperties.com/references/MechPropHandouts.pdf 15. C.E. Inglis, Proceedings of 54th Session Institution Naval Architects (1913), pp. 219–241 16. A.A. Griffith, Philos. Trans. R. Soc. Lond. A221, 163–198 (1921) 17. V.F. Solinov, Glass Ceramics 72(5–6), 191–193 (2015) [Translated from Steklo i Keramika 6, 5–8 (2015)] 18. W. Rudolf, Proceedings on Glass Processing days (1997), pp. 40–43 19. N. Pourmoghaddam, J.H. Nielsen, J. Schneider, Engineered Transparency Conference (2016). https://www.researchgate.net/figure/2-Sketch-of-the-process-line-for-tempering-floatglass_fig2_323308731 20. K. Varshneya Arun, Int. J. App. Glass Sci. 1(2), 131–142 (2010) 21. C. Carrot, A. Bendaoud, C. Pillon, in Handbook of Thermoplastics eds. by O. Olabisi, K. Adewale (2015), p. 122. https://www.routledgehandbooks.com/doi/https://doi.org/10.1201/ b19190-4 22. J.H. Nielsen, Olesen · J F and Stang H. Exp. Mech. 49, 855–870 (2009) 23. L. Hill, How to Choose Between Laminated Versus Tempered Safety Glass (2016). https://info. glass.com/laminated-vs-tempered-glass/ 24. G. Ding, C. Clavero, Modern Technologies for Creating the Thin-film Systems and Coatings (INTECH Open Science, 2017), pp. 409–431. http://dx.doi.org/https://doi.org/10.5772/67085 25. Guardian Sunglass—tech Info. https://www.glaziers27.org 26. Efficient Windows Collaborative: Low -e window technology. https://cdn.ymaws.com/www. rfmaonline.com/resource/resmgr/crfp/windowtechnologieslow-ecoati.pdf 27. J. Rissman, H. Kennan, Case Studies on the Government’s Role in Energy Technology Innovation: Low-Emissivity Windows (American Energy Innovation Council, 2013). http://americ anenergyinnovation.org/wp-content/uploads/2013/03/Case-Low-e-Windows.pdf 28. A basic Guide to Low-E Windows. https://www.slideshare.net/worldsgreatestwindow/a-basicguide-to-low-e-windows 29. “India Energy Efficient Glass Industry Business and Investment Opportunities Data book 2019” by ResearchAndMarket.com (2019). https://www.businesswire.com/news/home/201 90515005332/en/India-Energy-Efficient-Glass-Industry-Business-Investment 30. Singh Sunder reported in “Glass Worldwide” Issue No: 32 (2010) 31. Report on “Sectoral Manual-Glass Industry” prepared by TERI (2012). https://www.teriin.org/ sites/default/files/2018-02/Glass%20Report.pdf 32. https://auto.economictimes.indiatimes.com/news/auto-components/asahi-india-glass-to-startcommercial-production-at-taloja-float-glass-plant/61573323 33. https://in.ambafrance.org/Inauguration-of-Saint-Gobain-World 34. Saint Gobain Research India. https://sgrindia.saint-gobain.com/

The Status of Bulk Metallic Glass and High Entropy Alloys Research S. R. Reddy, P. P. Bhattacharjee, and B. S. Murty

1 Brief History of BMGs BMGs are amorphous alloys having several intriguing and outstanding properties [1– 7]. Pol Duwez (Klement et al. [8]) developed the first metallic glass (MG) by rapid quenching (gun quenching technique) of Au75 Si25 alloy liquid at cooling rates as high as ~106 K/s, thereby suppressing the nucleation of crystalline phases. Although several MGs have since been routinely fabricated by different processing routes [1, 2, 9, 10], they have always been limited by their size due to the necessity of achieving very high cooling rates required for glass formation. Johnson et al. [9–13] have shown the effect of several parameters on the crystal to glass transition in metallic materials. The first BMG with size >1 mm was reported in Pd-Cu-Si ternary alloy by Chen et al. [14] using suction casting with low cooling rates of the order of 103 K/s. Turnbull et al. [15] developed a new criterion to improve the glass-forming ability (GFA) to overcome the barrier to develop glasses in bulk scale. With an increase in the glass transition temperature, the cooling rate required for the glass formation significantly decreases, thereby improving the possibility of making thicker materials. Further, Inoue and Masumoto [5, 16] have systematically investigated to develop multicomponent BMGs with conventional rare-earth elements like La-Al-Ni/Cu-Co at very low cooling rates using the GFA criterion. Johnson et al. [9, 17, 18] further shown insights into the rheological properties of BMGs leading to the advancement in these materials. These efforts have opened the door to a new class of quaternary and quinary BMGs with a wide variety of compositions and advanced properties. The trajectory of research publications on BMGs outlines the progress in this field (Fig. 1). Substantial progress has been made in these materials over

S. R. Reddy · P. P. Bhattacharjee · B. S. Murty (B) Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy, Telangana 502285, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_10

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Fig. 1 Year-wise global publications in the field of BMGs

the past two decades with the unearthing of several unique properties for highperformance applications including micro-electromechanical system (MEMS) and nano-electromechanical systems (NEMS). A brief review of the principles of BMGs is presented, emphasising the important developments in this domain along with the global and Indian contributions.

2 Formation and Structural Foundation for BMGs The transition of liquid metals to solid under favourable conditions promotes the formation of crystalline phases. On the other hand, extreme cooling rates (of the order of 106 K/s) can cause suppression of the nucleation and growth of crystalline phases in the supercooled liquids leading to the formation of amorphous phase. BMGs, on the other hand, form at significantly lower cooling rates, as low as 0.1 K/s. The major contributing factor to the formation of the bulk glassy alloys is the improved glass formatting ability (GFA) [5, 19] of the material. GFA is considered as the ratio between the glass transition (T g ) and the liquidus temperature (T l ). Improved GFA [5] along with effective stabilisation of supercooled liquid metal contributes to ease of BMG formation. The critical parameters associated with the improvement of GFA of BMGs are.

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(a) (b) (c)

235

addition of multiple alloying elements (typically more than three elements) with new local atomic configurations varying the atomic diameter of the constituent elements, i.e. large atomic diameter mismatch large negative mixing enthalpy

Elements with complex crystal structure prefer to inhibit crystallisation and promote glass formation. By suitably choosing the elements of the alloy, the supercooled liquid can be maintained stable for an extended time [1]. This gives an opportunity to understand the development of BMGs [1, 2, 20]. Enhanced stability of liquid melt allows the production of BMGs by various conventional processing routes including water quenching [14], suction casting [21], centrifugal casting [22], and Cu-mould casting [23]. Several other solid-state processing routes such as mechanical alloying (MA) or severe plastic deformation can successfully produce a wide variety of BMGs. The structure of BMGs greatly depends on the atomic packing of the alloying elements. The large atomic size difference promotes higher packing density, which in certain localised regions (icosahedral short-range order) can be even higher than that of the crystalline materials. The BMGs are found to have a homogeneously mixed yet high degree of randomly packed atomic arrangement with unique structure development. Inoue and Takeuchi [1] classified the BMGs into two types, namely, metal–metal-type alloys, and metal–metalloid type alloys. The configurations are different among the three types of BMGs [1]. The metal–metal-type alloys based on Zr, Fe, Cu and Ni consist of short-range icosahedral clusters (Frank-Kasper Clusters and Bernal clusters) providing an additional barrier for nucleation of crystalline phases. The highly dense packed structure retards the large-scale atomic mobility suppressing the crystallisation. In contrast, the metal-metalloid alloys consisting of Zr, Fe, Cu together with B, Si, C, P show a network of trigonal prisms interconnected through glue atoms. The Pd-metalloid (Si, C, P) type BMGs consist of large-sized clustered units of a trigonal prism capped with three half-octahedra for the Pd–Ni–P and a tetragonal dodecahedron for the Pd–Cu–P region. The coexistence of these two large clusters plays a pivotal role in stabilising the supercooled liquid [2, 5].

3 Physical and Mechanical Properties of BMGs BMGs possess excellent physical and mechanical properties including high strength, good corrosion resistance and magnetic properties. The most notable feature of the BMGs is the high strength and hardness at ambient temperatures in comparison to the crystalline materials [1]. These materials suffer from rather limited ductility at room temperatures due to their characteristic inhomogeneous deformation behaviour manifested by the formation of highly localised shear bands (Fig. 2a) [1, 2, 24– 26]. The schematic in Fig. 2b shows the deformation mechanism involving shear transformation zone for strain accommodation through a localised cluster of atoms

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Fig. 2 a Optical micrograph representing the formation of multiple shear bands in Ni50 Pd30 P20 BMG specimen subjected to compression testing [26]; b schematic representing the shear transformation zone in MGs [27]

undergoing intense distortion [27]. Localised heating at the shear bands is found to contribute to the thermal softening, effectively contributing to further local plastic deformation leading to a brittle failure [28, 29]. The localised temperature rise in the shear bands at the time of fracture for different BMG alloys is shown in Fig. 3a [15]. The catastrophic failure of BMGs has been considered to result from the sudden drop in viscosity inside the shear band as a result of local heating. The local temperature rise in shear bands has been observed to be very close to that of the glass transition temperature is typically observed in several BMGs (Fig. 3a). However, BMGs may likely show homogenous deformation behaviour at high temperatures due to the

Fig. 3 a Plot representing the localised temperature rise in the shear bands at the time of fracture for different BMG alloys [28]; b Schematic representation of various modes of deformation with temperature [30]

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Fig. 4 Comparison of tensile strength and hardness for typical BMGs with conventional alloys [5]

viscous flow behaviour [30], as schematically shown in Fig. 3b. Structural relaxation [31] induced by thermal treatments has also been observed in BMGs. Fe-based BMGs can even show high strength in comparison to steels and other crystalline alloys as compared in Fig. 6 [1, 5]. Greer et al. [32, 33] further proposed that the brittleness of MGs is similar to that of crystalline metals which correlates with the ratio (μ/B) of the elastic shear modulus (μ) to the bulk modulus (B) exceeding a critical value leads to brittleness. Madge et al. [33, 34] further showed that presence of oxide particles leads to inferior fracture toughness in several BMGs. However, some of the glassy alloys are profoundly brittle, irrespective of their Poisson’s ratio (ν) due to their complex alloy chemistry. La-based glassy composites [35] dispersed with Ti particles have shown appreciable compressive strength even under cryogenic conditions. The corrosion resistance of structural materials is important for critical applications. BMGs exhibit good corrosion resistance when compared to their crystalline counterparts. Fe-based Fe80−x Crx P13 C7 glassy ribbons exhibit much higher corrosion resistance than the crystalline Fe–Cr alloys [36]. Fe-based BMGs exhibited passive behaviour under extreme environmental conditions, while alloying with P results in further enhancement in corrosion resistance [37]. The addition of alloying elements like Mo, Nb or Ta significantly improves the corrosion resistance of the BMGs. BMGs exhibit good soft magnetic properties due to the absence of non-magnetic elements. However, the magnetic properties can be tailored by suitable heat treatment procedures. Fe-B glasses are generally used in electrical distribution transformer cores. Fe-based and Co-based BMG alloys display the desired amalgamation of low coercivity and high electrical resistivity [2] and are considered for good microformability which is very important for NEMS and MEMS applications.

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4 Advances in Applications Potential structural applications [38, 39] demand high-performance engineering materials with high strength, high elastic limit, and low density. Zr-based BMG materials [40] are extensively used for sporting materials including golf clubs, baseball bats, skis and tennis rackets [2]. BMGs are highly biocompatible and are indispensable in the medical field [41]. They are widely adopted for prosthetic implants and joint replacements due to their high wear and corrosion resistance [42] originating from the absence of grain boundaries. Magnesium-based BMGs that can be used for biodegradable implants signify recent developments in biomedical applications. The soft magnetic materials prepared using BMGs have potential applications in electronic devices. A wide range of applications including the energy storage and conversion activities require good electro-catalectic activity, so that noble metalbased BMGs [43] are promising candidates for the purpose. BMGs possess excellent softening at higher temperatures required for fabricating micro/nano-patterns and devices with high precision. Nano-architectured materials made out of BMGs greatly enhance the use of these materials for sensing, NEMS and MEMS applications [38, 44].

5 Indian Contributions The MG research in India was initiated by Prof. Anantharaman at BHU [3, 7, 45, 46]. The successful preparation of MGs by Ramachandra Rao [3, 47, 48] has been the starting point for MGs in India. The insights into the MGs from the conventional alloying approaches are shown by Ranganathan [4]. Ramachandra Rao et al. [47, 48] have shown the effect of undercooling on the free energy of metallic alloys based on the hole theory of liquids in glass-forming alloys. The initial contributions to MG research from India came from BHU followed by IISc. Ranganathan et al. [49] have extensively contributed to the determination of the glass-forming range (GFR). The actual GFR is found to be smaller than the theoretical predictions (Fig. 5), which is confirmed by MA in the ternary Ti–Ni–Al system [49]. Prolonged milling of the amorphous Ti50 Ni25 A125 powders led to the reappearance of the crystalline peaks. Ramamurthy et al. [50–52] have significantly contributed towards the understanding of the mechanical behaviour of BMGs. They have performed several studies on the embrittlement behaviour of BMGs following low-temperature annealing treatments. A marked loss of the impact toughness as shown in Fig. 6 due to the structural relaxation resulting from the free volume reduction in the materials has been highlighted [50]. Several indentation-based studies [53–55] on the BMGs have greatly contributed towards the understanding of their intriguing plastic deformation characteristics by Prof. Chattopadhyay and co-workers. Jana et al. [54, 56] have studied the subsurface

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Fig. 5 Ternary diagram showing the calculated glass-forming composition range (GFR) in the Ti-Ni–Al system obtained using the Miedema model [49]

Fig. 6 Impact toughness (J) as a function of a annealing time (383 K) and b annealing temperature with a fixed time of 24 h [50]

deformation behaviour of BMGs using bonded interface technique and Vickers hardness. BMGs deform significantly through shear band mechanism under applied load. Ramamurty et al. [55] have systematically studied the plastic deformation behaviour under indentation that revealed inhomogeneous shear-banded regimes around the indentation. The pressure-sensitive plastic flow exhibited by MGs resulted in smaller indentation sizes, whereas annealed materials show the absence of wide plastic zones causing the embrittlement of these materials. They have also pioneered early work on wear [57] and welding behaviour of the BMGs. Mukhopadhyay et al. [58] studied the Nanoindentation behaviour of Cu47 Ti33 Ni6 Sn2 Si1 BMG processed by injection

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casting. The plastic deformation of this glassy material appears to proceed by the shear band formation and propagation in a stepwise manner. Nanocrystallization was observed beneath the indenter suggesting the pressure-induced phase transformation in these materials. Further a hierarchical composite could be synthesised by Park et al. [59] using phase separating systems exhibiting the entire spectrum of microstructural possibilities. The resulting microstructures consist of a novel core–shell and hierarchical structures of spherical glassy droplets, resulting from critical wetting behaviour and limited diffusion (Fig. 7a). Modelling studies (Fig. 7b) by Park et al. [59] further confirm the evolution of the hierarchical microstructure in the glass composites. Narasimhan et al. [60, 61] proposed ductility enhancement strategies in BMG composites based on continuum analyses of tensile loading. Based on the results they have proposed that high hardening elongated dendrites [61] with significant volume fraction would make the BMG composites ductile without any loss of any strength. Gouripriya and Tandaiya [62] recently reported that Shape Memory Alloy (SMA) reinforced BMG matrix composites show improved work hardening behaviour. The synergistic effects of phase transformation and elastic loading of transformed martensite in SMA particle lead to the improved work hardening rate. Jana et al. [56] have performed extensive studies on the deformation morphology in a Zr-based BMG at various annealing temperatures and stress levels. Appreciable plastic deformation through shear banding was found to occur in the as-cast and annealed alloys. Two different types of shear bands were reported [32]. Their occurrence is found to depend upon the extent of crystallisation. The fully crystallised alloy exhibited extensive cracking (Fig. 8). The shear band morphology in the ascast sample is found to agree with the slip line field theory [63]. The negative strain rate sensitivity indicates that the deformation behaviour in this BMG is dominated by shear-band-mediated inhomogeneous plastic flow [64].

Fig. 7 a TEM micrograph obtained from as-melt-spun Ti45 Y11 Al24 Co20 and b phase-field modelling showing the evolution of a hierarchical microstructure [59]

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Fig. 8 Micrographs representing the subsurface deformation zones underneath the Vickers indenter: a and b as-cast alloys exhibiting a semi-circular shear band morphology. c annealed alloy; d fully crystallised alloy showing extensive cracking [56]

Basu et al. [65] have pursued the synthesis of new BMGs by using the thermodynamic principles. Mondal and Murty [66] proposed a new parameter to assess the GFA of liquid and the relation on the thermal stability of the glass. They have incorporated thermodynamic and topological parameters including GFA to identify and produce the BMG forming compositions in different alloy systems. Bhatt et al. [67] have used mechanical alloying (MA) for the synthesis of the BMGs and further studied the mechanical properties of the materials. The milling speed, ball to powder weight ratio have been shown to exert a significant effect on the formation

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of the amorphous phase [67, 68]. The total milling energy had a decisive role than the impact energy of the ball in the formation of the amorphous phase during MA (Fig. 9) [67, 68]. Prediction of glass-forming compositions of different alloy systems using Miedema’s approach [65, 69] has been one of the important contributions of their research work. The best glass-forming compositions have been identified by drawing iso-Gibbs energy change contours (Fig. 10) by representing quinary systems as pseudo-ternary ones. Das et al. [70, 71] developed new BMG composites [72] and evaluated their deformation behaviour and mechanical properties. Addition of 5 at.% Al to the Cu50 Zr50 glass has been found to increase the yield strength significantly from 1272 to 1547 MPa and improved the room temperature deformability from 8 to 18%, as shown in Fig. 11 [70]. The unique work hardening capability originates from the

Fig. 9 Milling maps indicating the energy required for amorphisation in a Zr65 Al7.5 Cu17.5 Ni10 and b Fe56 Co7 Ni7 Zr10 B20 [67]

Fig. 10 a Iso-Gibbs free energy contour map for the Zr–Ti-Ni–Cu–Al system; b The correlation between G and total energy required for amorphization by milling in different Zr and Ti-based alloys [69]

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Fig. 11 TEM high-resolution images of a Cu50 Zr50 with tiny crystallites of glassy phase b Amorphous structure of Cu47.5 Zr47.5 Al5 (inset: SAED patterns); c Corresponding stress–strain curves of Cu50 Zr50 and Cu47.5 Zr47.5 Al5 (inset: true stress– strain curve of Cu47.5 Zr47.5 Al5 ) [70]

atomic-scale inhomogeneity in the composite. This results in a homogenous shear band formation and continuous multiplication during plastic deformation. These interactions of the shear bands result in an increased flowability of the BMGs [70]. Mondal et al. [66, 73] have been involved in the thermodynamics and kinetics of glass formation of the amorphous and nanocrystalline Zr alloys. They have designed a few thermodynamic models to understand the basis for glass formation and understanding the corrosion and oxidation behaviour of these materials. Their recent studies include the development of BMG coatings and their corrosion and wear resistance applications. Madge et al. [74] have developed exceptionally wear-resistant and refractory W-based glassy (W33 Ni32 B3 ) coatings which have the potential to replace TiN coatings. Sharma et al. [75, 76] have extensively worked on the oxidation [75, 77] and corrosion behaviour [76] of Zr-based BMG materials. Effect of ion implantation on the corrosion behaviour of these materials is probed in depth. Further potentiodynamic polarisation studies [78] on Zr46.75 Ti8.25 Cu7.5 Ni10 Be27.5 and Zr65 Cu17.5 Ni10 Al7.5 revealed the effect of constituent alloying elements on the native surface leading to differential corrosion. Manna et al. [79, 80] have extensively worked on the laser surface cladding of Fe-based amorphous layer on steels to improve the wear and corrosion resistance of commercial steels. Although improvement in these properties is observed, these materials have failed to retain amorphous microstructure due to the compositional fluctuations in the coating zone and interface [80]. These coatings with proper control of microstructures can produce materials with improved wear and corrosion properties. Srivastava et al. [81–84] worked on the spray forming process on amorphous

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glassy materials. Spray forming of the glass-forming Al83 Y5 La5 Ni5 Co2 material led to the development of nanocrystalline matrix composites with the presence of significant fraction of amorphous phase. Further investigations show that cooling rate [85] during spray forming along with surface temperature of deposit plays a critical role in the development of BMGs. Vora et al. [86, 87] extensively studied the electrical properties in metallic glasses and BMGs using different theoretical models. They have predicted the presence of superconductive behaviour in the BMGs using pseudopotential-based formulation. Other research groups have also contributed significantly to the application of the BMG for novel structural applications [81]. The research contributions in BMGS from different research groups are summarised in Table 1. The recent publication statistics of the Indian scientific community indicates a strong presence in the global field with 284 odd publications to date (see Fig. 12). Although the growth of publications has apparently subsided possibly reflecting the maturity of knowledge, significant gap areas in understanding the mechanical properties of the materials still exist. Recent developments in this field including additive manufacturing of BMGs and their composites signify the emergence of new research areas with potential for advanced/ breakthrough applications.

6 Brief History of HEAs The conventional alloys are mostly based on one or two-based elements with the alloying elements added in dilute proportions and hence are confined to narrow region of the possible composition space. In contrast to the conventional alloys based on one major element, HEAs have been independently developed by Yeh et al. [90] and Cantor et al. [91] as multicomponent systems (usually ≥5) with equiatomic or near equiatomic concentrations. Despite containing a large number of elements, the HEAs may yet show rather simple solid solution phases FCC [90–93], BCC [93– 95], HCP [93, 96] or FCC + BCC [90, 97–99]. It has been argued that the increased configuration entropy (Smi x = Rlnn, for an equiatomic n component system) can sufficiently reduce the free energy (G mi x ), thereby favouring the formation of solid solution phases over intermetallic phases. Based on the configuration entropy, alloys can be categorised into low, medium and high entropy alloys (Fig. 13a) [100]. Recently, the definition of HEAs has been relaxed to consider non-equiatomic compositions, thereby opening the massive composition space located at the central regions of the hyper-dimensional composition space for developing alloys with unprecedented properties (Fig. 13b). Consequently, alternative nomenclatures such as complex concentrated alloys or compositionally complex alloys have been used in recent literature to effectively highlight these aspects [101, 102]. Of late, the field of HEAs transcends metallic alloys, thereby giving birth to high entropy materials (HEMs) including but not limited to high entropy carbides, nitrides and di-borides [103]. In essence, HEAs and HEMs have emerged as new frontiers in materials

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Table 1 Indian researchers and their research interests in BMGs Area of Research

Research Groups

Theoretical prediction and synthesis of BMGs

S. Ranganathan, IISc Determination of Bangalore glass-forming range, B. S. Murty, IIT new GFA parameters Madras J. Bhatt, VNIT Nagpur B. Majumdar, DMRL Hyderabad K.L. Sahoo, NML Jamshedpur

Main Contribution

Refs. [49, 66]

Mechanical behaviour of BMGs

U. Ramamurty, IISc Banglore J. Das, IIT Kharagpur

Embrittlement behaviour of BMGs due to free volume reduction

Ramamurty et al. [50]

Thermodynamics and B. S. Murty, IIT Kinetics of BMGs Madras K. Mondal, IIT Kanpur

Prediction of glass-forming compositions using Miedema’s approach

[65, 69]

MA of BMGs

J. Bhatt, VNIT Nagpur B. S. Murty, IIT Madras I. Manna, IIT Kharagpur

Development of milling maps during MA, Laser surface cladding of BMG coatings to improve resistance of the substrate to wear and corrosion

[67, 79]

Corrosion and wear behaviour of BMGs

K. Mondal, IIT Kanpur U. K. Mudali, IGCAR Kalpakkam S. K. Mishra, NML Jamshedpur S. K. Sharma, MNIT Jaipur

Development of amorphous Zr55 Ti25 Ni20 alloy with better corrosion resistance, Exceptionally wear-resistant and refractory W-based glassy coatings

[73, 74]

BMG based nanocomposites

J. Das, IIT Kharagpur R. Narasimhan, IISc Bangalore

Development of BMG [61, 70] composites with enhanced work hardening capability, Finite element simulations to develop BMG composites with improved ductility

Crystallisation of BMGs

G. K. Dey, BARC Mumbai N.K. Mukhopadhyay, IIT BHU

Identification of conditions for the formation of nanocrystals

Neogy et al. [88]

(continued)

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Table 1 (continued) Area of Research

Research Groups

Main Contribution

Magnetic behaviour Superconductivity of BMGs

B. Majumdar, DMRL Hyderabad A. Mitra, NML Jamshedpur A. M. Vora, Gujarat University

Nano crystallisation [86, 87, 89] for optimization of magnetic properties in BMGs, Theoretical predictions on the superconductive behaviour of metallic glasses

Refs.

Fig. 12 Year-wise Indian publications in the field of BMGs

Fig. 13 a Classification of HE alloys based on configurational entropy [100]. b Schematic distinguishing conventional and high entropy approaches. The conventional alloys are located at the corners and along the edges, while the HEAs are located at the central regions (indicated by the circled region) of the hyper-dimensional phase diagrams

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Fig. 14 Year-wise global publications in the field of HEAs

research [104–108]. These developments are adequately reflected in the publication trajectory, as summarised in Fig. 14.

7 Core Effects in HEAs There are several/core effects that are less dominant in conventional alloys but are considered to have a significant impact on the microstructure physical and mechanical properties of the HEAs. These key effects, viz., (i) high entropy, (ii) sluggish diffusion, (iii) severe lattice distortion and (iv) cocktail effects [109] are summarised below.

7.1 High Entropy Effect The perceived role of high entropy in stabilising solid solution phases has been first highlighted by Yeh et al. [90]. The early experimental evidence has been presented to argue that high entropy effect can actually extend the solid solubility limit [105] favouring the formation of disordered solid solutions [110]. However, more recent results have indicated that high entropy effect may not sufficient for ensuring solid solution formation. Otto et al. [111] have critically examined the effect of chemical composition on phase stability in the well-known FCC CoCrFeMnNi system [91]. The individual elements are replaced systematically by chemically and structurally similar elements (for, e.g. Cu for Ni, Ti for Co, Mo or V for Cr). It has been observed that a single-phase system cannot prevail in majority of the compositions. Recently,

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single-phase non-equiatomic HEAs have also been reported with promising properties such as high temperature strength and good oxidation resistance [112]. Therefore, not all equiatomic multicomponent systems show simple solid solution phases, and at the same time, non-equiatomic systems can also exist as a single phase [113]. Therefore, the studies pertaining to rules governing the phase formation criteria are to be continued.

7.2 Severe Lattice Distortion Effect Severe lattice distortion in HEAs is contributed by the difference in atomic sizes of the elements. Consequently, the displacement at any given atomic site is affected by that particular site and the local atomic environment (Fig. 15) [92]. In addition, different bonding energy and crystal structure amongst the constituent elements may contribute to lattice distortion. As a result, the overall lattice distortions could be more severe in HEAs as compared to that in the conventional alloys. This was reflected in the reduced intensity of X-ray diffraction peaks [92, 114, 115], increased hardness [92, 115], reduced electrical and thermal conductivity [92, 115]. The severe lattice distortion can further reduce the temperature dependence of the properties such as diffusion and creep resistance [92, 115]. Fig. 15 Two-dimensional matrix of a solid solution HEA with 10 different components. Two vacancies are also shown. The average lattice is shown by the interconnected lines [92]

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7.3 Sluggish Diffusion Effect The sluggish diffusion effect in HEAs is one of the most intensely contested aspects. In the formative years of HEAs, it was considered that the movement of an atom in the HEA matrices would be considerably more difficult than in the matrices of conventional alloys [90]. Interestingly, the diffusion coefficients of different elements at the same homologous temperature (T/Tm ) in the CoCrFeMnNi HEA are much lower as compared to the corresponding values in different FCC alloys [116]. The sluggish diffusion effect in the experimental HEA appears to be manifested by the significantly higher value of Q/Tm of the constituent elements in the HEA as compared to those in the elemental state and in conventional alloys (Fig. 16). Slower diffusion and higher activation energy are thought to originate from the larger fluctuation of lattice potential energy (LPE) between lattice sites in HEAs. The abundant low-LPE sites could effectively act as traps and hinder the diffusion of atoms [116]. Nevertheless, recent investigations have disagreed on the validity of the sluggish diffusion effect [101] by reinterpreting the data reported by Tsai et al. [116]. These results indicate that diffusivity DNi in CoCrFeMn0.5 Ni is comparable to other conventional materials at the same temperature (Fig. 17a). However, the diffusion coefficients appear to be lower in CoCrFeMn0.5 Ni than in selected FCC elements Fig. 16 Melting-point normalised activation energy of diffusion for Cr, Fe, Mn, Co and Ni in different matrices [116]

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Fig. 17 Diffusion coefficients of Ni (DNi ) in FCC elements, stainless steel alloys (compositions in the legend are shown in at.%) and CoCrFeMn0.5 Ni as a function of a inverse absolute temperature, and b inverse absolute temperature normalised by the melting or solidus temperature of the host alloy, Tm. In (b), all DTm values measured in CoCrFeMn0.5 Ni (for Co, Cr, Fe, Mn, and Ni) are shown to fall within the range of DTm values for a broad range of FCC metals and alloys [101]

and conventional alloys, when the activation energies are normalised by the melting point or solidus temperature Tm (Fig. 17b) as already emphasised before (Fig. 16). Therefore, diffusion in HEAs may not be considered significantly sluggish. Further investigations need to be carried out in a wide range of HEAs to better understand and clarify the sluggish diffusion aspect [101].

7.4 Cocktail Effect The concept of ‘multimetallic cocktails’ has been hypothesised by Ranganathan [117]. For metallic alloys, the cocktail effect is qualitatively perceived as a nonlinear synergistic effect on properties obtained after mixing many elements, which might not be obtained from any one element alone. It can be understood from the ‘cocktail effect’ that the exceptional materials properties often result from unexpected synergies. Therefore, the final properties of the HEAs could be affected by the overall contribution of the constituent elements [92, 118]. These synergistic responses which are rather difficult to quantify may be instrumental in achieving intriguing mechanical and physical properties [101].

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8 Phase Formation in HEAs A major issue in developing novel HEAs is understanding the thermodynamic guiding principles for phase formation and stability. Following Hume-Rothery rule, atomic size difference (δ) and enthalpy of mixing (Hmix ) are considered as the key parameters with regard to phase stability [119, 120]. These parameters are given by the following equations:   n n   δ= x i . 1 − ri

i=1

i=1

Hmi x =

n 

x i · ri

mi x 4.H AB .xi .x j

2 (1)

(2)

i=1,i= j

mi x is the enthalpy of mixing where ri is the atomic radius of the ith element and H AB for binary A and B elements in the alloy system. The δ − H mi x plot (Fig. 18a) [121, 122] highlights the phase selection in HEAs, as followed from the Eqs. 1 and 2. The plot shows that solid solutions formation is favoured when the mixing enthalpy is either negative or slightly positive (−12 < small (δ < 6%). The Hmi x < 5 kJ/mol) and atomic size difference (δ) is relatively amorphous phase is favoured when Hmi x < −12 kJ mol and δ is large (δ > 6%). The intermetallic compounds are favoured at intermediate conditions overlapping the solid solution region and amorphous region. Another important criterion to predict the formation of solid solution phases in HEAs is ‘’, which represents the effect of entropy relative to enthalpy. For a multicomponent alloy the mixing enthalpy (H mi x ) is an average of the alloy system, whereas the entropy part (−T.S mi x ) should be sufficiently negative to stabilise the

Fig. 18 Illustrative plots of a δ − H mi x and b  − δ outlining the phase selection and formation in multicomponent alloys [121, 123]

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solid solution phases in the system. Thus, the ratio of the entropy and enthalpy is given by  = Tm · Smi x |Hmi x |.

(3)

where T m (in Kelvin) is the melting temperature of the alloy containing ‘n’ alloying elements measured from the rule of mixture. Based on Eq. 3, higher (> 1) is favourable for the formation of a solid solution phase in the HEAs. The  − δ plot (Fig. 18b) shows the zone of the formation of solid solution phases. The presence of solid solution is preferred when  ≥ 1.1 and δ ≤ 6.6%, which evidently follows a hyperbolic relationship [123] (δ × ln  = constant), as shown by the dotted lines in the plot. Furthermore, an increase in δ(> 6%) or a decrease in (< 1) results in the stabilisation of intermetallic compounds and amorphous phases. Valence electron concentration (VEC) [124] has also been found to be a critical parameter for determining the phase formation in HEAs. Guo et al. [125] first proposed the VEC concept to determine the FCC and BCC phase stability in HEAs, which was later extended to non-equilibrium phases like (e.g. σ phase formation) [126]. The VEC in a multicomponent alloy is given by V EC =

n 

xi .(V EC)i

(4)

i=1

where (V EC)i is the VEC of the ith element. It has been found that single-phase BCC is favoured when V EC ≤ 6.8, while the formation of single-phase FCC is favoured when V EC ≥ 8.0. A two-phase FCC + BCC mixture is favoured in the intermediate region (6.8 ≤ V EC ≤ 8.0).

9 Classification of HEAs The major classification includes single-phase transition metal HEAs, refractory HEAs, eutectic HEAs, metastable HEAs, HE-super alloys, HE-BMGs and others. The present section provides a summary of these HEAs.

9.1 Transition Metal HEAs The transitional metal HEAs are the largest group consisting of Co, Cr, Cu, Fe, Mn, Ni, Ti and V. The first HEA developed is the Cantor alloy (CoCrFeMnNi) with a

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single-phase FCC structure [127]. These HEAs can be further modified by interstitial or substitutional alloying elements to alter their microstructure and mechanical properties. The different subclasses of the transition metal HEAs are summarised below. (a)

(b)

(C)

(d)

Eutectic HEAs: Eutectic HEAs (EHEAs) are a special subgroup of 3d- transition metal HEAs first proposed by Lu et al. [128]. AlCoCrFeNi2.1 consisting of a lamellar arrangement of L12 + B2 remains one of the most widely investigated HEAs. These EHEA can be successfully processed by a wide variety of thermo-mechanical routes to achieve novel heterogeneous microstructures and ultra-high-strength properties. Nobel metal HEAs: HEAs comprising Nobel metals are another subclass of HEA having considerable potential for catalytic applications. Both single (PdPtRhIrCuNi) and dual-phase (AuPdAgPtCuNi) noble metal HEAs have been reported. High Entropy superalloys: These are meant for superior high-temperature strength and creep strength for high-temperature applications. The critical requirements for superalloys are the presence of uniformly distributed γ / (L12 ) particles coherent with the FCC γ matrix and long-term stability of these phases. FCC matrix strengthened by a uniform distribution of nano-sized γ / precipitates (volume fraction ~20–40%) has been reported in Al8 Co17 Cr17 Cu8 Fe17 Ni33 and Al10 Co25 Cr8 Fe15 Ni36 Ti6 HEAs (Daoud et al.) having improved tensile strength in comparison to commercial superalloys, such as Inconel 617 and 800H. Some of the HE-superalloys also show promising oxidation and creep resistance, comparable to conventional superalloys [129]. Metastable HEAs: Metastable HEAs are compositionally tuned to trigger different deformation mechanisms for simultaneous improvement in strength and ductility. The prime example is the Fe50 Mn30 Co10 Cr10 alloy reported by Li et al. [130] using metastability engineering (Fig. 19). The compositional tuning ensures two key effects, namely, interfacial strengthening due to (FCC + HCP) dual phase (DP) microstructure and transformation-induced strengthening.

9.2 Refractory HEAs Refractory HEAs (RHEAs) consisting of high melting refractory elements like Hf, Mo, Nb, Ta, Ti, V and W are primarily developed for high-temperature applications [94]. However, poor oxidation resistance of RHEAs remains a challenge to be overcome for their applications at high temperatures. Although recent studies show that the addition of Al can improve oxidation resistance [131], further developments necessitate compositional adjustments and microstructure control for rendering RHEAs suitable for high-temperature applications.

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Fig. 19 a Tensile behaviour of the TRIP-DP Fe50 Mn30 Co10 Cr10 HEA (Inset shows the X-ray diffraction and microstructure). b Schematic of the deformation structure in the TRIP-DP HEA [130]

9.3 High Entropy Metallic Glasses BMGs and HEAs share certain distinct similarities with respect to compositional complexities. Although both these material classes are characterised by multicomponent nature, BMGs are generally pseudo-binary alloys, unlike HEAs. High entropy BMGs (HE-BMGs) are considered to be those containing five or more elements with equiatomic or near equiatomic proportions [132, 133]. The typical synthesis routes for the conventional BMGs could be successfully extended to synthesise HEBMGs. Pd20 Pt20 Cu20 Ni20 P20 [133] was the first HE-BMG developed by fluxed water quenching which opened a new field of HE-BMGs. HE-BMGs such as TiZrCuNiBe [134] showed higher glass transition temperature (Tg ) and initial recrystallisation temperature (Tr ) than conventional Ti or Zr-based conventional BMGs, indicating high thermal stability of the HE-BMGs [134]. Nevertheless, annealing HE-BMGs such as TiZrCuNiBe resulted in a complete breakdown of the amorphous structure into a multiphase mixture of FCC, BCC and Ni7 Zr2 phases.

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9.4 Light Metal HEAs Lightweight HEAs with possible applications in aerospace and transportation sectors signify a distinct trend in the design and development of novel HEAs [96, 135, 136]. These HEAs primarily contained low-density elements (such as Al, Be, Li, Mg, Sc, Si, Sn, Ti and Zn). Nanocrystalline lightweight HEAs, such as Al20 Li20 Mg10 Sc20 Ti30 prepared by MA showed remarkable strength to weight ratio and significant potential for further development [96].

9.5 Other HEA Classes HEAs based on lanthanides, namely, Dy, Gd, Lu, Tb and Tm alloyed with elements such as Y have also been investigated in recent times. Remarkably, the two HEAs YGdTbDyLu and GdTbDyTmLu revealed the presence of the HCP single phase [137]. The microstructure and properties of the HCP HEAs have not been investigated in-depth. Several new alloys based on high entropy concept like HE-steels [138], HEbronzes [139] are being developed that show superior properties in comparison to conventional alloys.

10 Deformation Behaviour of HEAs A major driving force for the accelerated research witnessed in the area of HEAs is developing materials with superior mechanical properties at temperatures ranging from cryogenic to high temperatures. Therefore, the deformation phenomena of the major classes of HEAs including 3d-transition metal HEAs, refractory HEAs, dual-phase HEAs and others remain as key issues [140].

10.1 Summary of General Observations In general, the yield strength of 3D-transition metal HEAs [140] such as CoCrFeMnNi (indicated as HEA-1) is low compared to HEAs containing bigger atoms such as Al (indicated as HEA-2 in Fig. 20, which may undergo a phase transformation from FCC to dual-phase FCC + BCC or completely BCC with increasing Al addition) and refractory metal HEAs (indicated as HEA-3 in Fig. 20). However, the high-temperature yield strengths of these HEAs are rather unsatisfactory, while selected refractory HEAs show better high-temperature mechanical properties. The deformation behaviour is also affected considerably by the crystal structures of the constituent phases in the HEAs. The FCC HEAs [99] usually show low yield

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Fig. 20 Comparison of the yield strengths as a function of the temperature of three typical types of HEAs with selected conventional alloys [140]

strengths but significant work hardening (Fig. 21a). Increasing Al addition results in the gradual transformation from FCC to FCC + BCC [99] and finally to completely BCC structures with increased yield strength at the cost of ductility (Fig. 21a). On the other hand, refractory BCC HEAs [141] show very high yield strength but low ductility (Fig. 21b). The cryogenic deformation behaviour of FCC HEAs is often featured by the appearance of pronounced serration in the stress–strain curve [142]. The tensile plots of HEAs [143] (Fig. 22) tested at cryogenic temperatures clearly show simultaneous enhancement of strength and ductility.

Fig. 21 Tensile stress–strain behaviour of a Alx CoCrFeMnNi [99] and b refractory HEA HfNbTiZr [141]

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Fig. 22 Temperature effect on the stress–strain behaviour of a CoCrFeNi; b CoFeMnNi and (C) CoCrMnNi HEAs [143]

10.2 Fundamental Deformation Phenomena The relative importance of the two major deformation modes, namely, slip and twinning has been investigated intensely in HEAs using the CoCrFeMnNi and their derivatives with single-phase FCC structures as model systems. The {111} < 110 > has been confirmed to be the primary slip system for FCC HEAs. Presence of both undissociated ½ < 110 > dislocations and stacking faults due to the dissociation of perfect dislocations into 1/6 < 112 > Shockley partials have been confirmed. On the other hand, experimental studies on dislocation configurations in BCC HEAs are rather limited. However, the wavy configuration of the gliding dislocations appears to be affected by the local composition and core structure [144]. The formation of deformation twins in FCC HEAs considerably affects the mechanical behaviour of HEAs. Deformation twin formation is accelerated by low SFE, low temperature, coarser grain size and high strain rates of deformation. For example, CoCrFeMnNi alloy with starting grain size ~4.4 μm shows the formation of nanoscale deformation twins after ~20% elongation at 77 K, while the same alloy with a much coarser starting grain size ~155 μm reveals the activation of secondary twinning systems beyond ~38% elongation [142]. The remarkable effect

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of deformation twins on the mechanical behaviour of single-phase FCC HEAs is also manifested by the exceptional tensile and fracture strength at cryogenic temperatures [145, 146]. Although single-phase BCC HEAs also show the formation of deformation twins [95], the understanding is significantly lacking when compared to their FCC counterparts.

11 High Entropy Materials The concept of designing HEAs has been expanded to include a host of other materials including nitrides, oxides and carbides. These are further expanded to HE composites including cermets and cemented carbides with HEA matrix as the binder phase.

11.1 High Entropy Oxides High entropy oxides (HEOs) have received considerable attention after Rost et al. [147, 148] synthesised the first HEO consisting of MgO, CaO, NiO, CuO and ZnO. The phase analysis showed that full conversion to a rock salt structure occurred between 850 °C and 900 °C without any further change in structure even after annealing at 1000 °C. Further, the structural transformation showed perfect reversibility such that the material equilibrated at 1000 °C transformed back to multiple phases when annealed at 750 °C and again converted to single-phase due to annealing at 1000 °C. EDF analysis revealed uniform spatial distribution for each element (Fig. 23) in the multicomponent oxide [147]. While the synthesis of different HEO materials has gained considerable momentum [149], the novel functional properties of these HEOs such as enhanced exchange coupling in HEOs [150] are only unfolding. The discovery of more such outstanding properties should fuel further research interests in developing and understanding the behaviour of novel HEOs [151].

11.2 High Entropy Nitrides, Carbides and Borides Chen et al. [152] successfully synthesised high entropy nitride (HEN) coatings using DC magnetron sputtering technique. Subsequently, HEN coatings were successfully deposited on different substrates by various techniques including DC magnetron sputtering [153], RF sputtering [154], plasma-based ion implantation and cathodic-arcvapour-deposition [155]. Extremely high hardness of ~48 GPa was obtained for the RF magnetron sputtered (TiVCrZrHf)N HEN coating. In addition to potential use as hard coatings with superior tribological properties, HENs have also gained attention

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Fig. 23 HAADF image of the multicomponent oxide. The EDS maps show uniform distribution of Mg, Co, Ni, Cu and Zn [147]

for other advanced applications including use as a diffusion barrier in interconnects and as a protective coating layer for cutting tools.

11.3 High Entropy Composites High entropy metal matrix composite (HECs) was first reported by Fan et al. [156] consisting of FeCrNiCoAlCu as the HEA matrix and TiC particles. The TiC particles were uniformly dispersed in the HEA matrix, resulting in remarkable improvement in the compressive strength. Subsequently, a significant number of different HEA matrix composites reinforced by particulates of carbides, oxides, silicides or fibres with superior mechanical properties were successfully synthesised. On the contrary, metal matrix composites were also prepared using different HEAs as the reinforcing phases by Chen et al. [157]. They have investigated the effect of nanocrystalline AlCoCrFeNi HEA reinforced in the copper matrix by the powder metallurgy route. Remarkable enhancement in compressive yield strength was observed in the copper matrix due to nanocrystalline AlCoCrFeNi HEA [157] as shown in Fig. 24. He et al. [158] have explored the possibility of developing high entropy-based cemented carbides with enhanced properties. CoCrNiCuMn HEA was used for binding TiN and TiC hard particles using spark plasma sintering (SPS) route. High hardness of ~ 15 GPa and excellent fracture toughness of ~7 MPa m−1/2 were reported.

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Fig. 24 Compression stress–strain curves for the Cu base composite without and with 10 wt. and 20 wt.% AlCoNiCrFe HEA [157]

12 Indian Contributions to the Field of HEA India has played a significant role in the development of HEAs. It is interesting to note that even before Yeh et. al. published their work on HEAs in 2004 [90], Ranganathan in his well-known paper published in 2003 [159] used the term HEAs followed from his personal communication with Yeh. In fact, Ranganathan [159] predicted the massive impact of these new classes of materials. Another glaring example of Indian contribution is reflected in the fact that the first published book internationally on HEA was co-authored by Murty, Ranganathan along with Yeh [92]. Bhattacharjee later joined in co-authoring the second edition of the book [103]. In the recent few years several international reviews [160–169] and book chapters [170–172] specifically focusing on HEAs and their related processing techniques are put forward by the Indian community. Very recently a viewpoint set [173] on the recent advancements and breakthrough ideas in HEAs are published. HEA work in India was pioneered by Murty and his group at IITM by the synthesis and characterisation of HEAs through MA [174, 175]. The possibilities of synthesising nanocrystalline HEA by MA were demonstrated by them for the first time (Fig. 25a). The XRD patterns show the gradual evolution of single-phase nanocrystalline BCC AlFeTiCrZnCu HEA obtained by MA [174]. The TEM micrograph (Fig. 25b) confirms the single-phase nanocrystalline structure of the MA-synthesised HEA. Vaidya et al. [176] also introduced a novel approach of synthesis of HEAs via MA termed as sequential alloying (Fig. 26). Interestingly, the amount of FCC and BCC phases varied in mechanically alloyed AlCoCrFeNi depending on the sequence of alloying element addition. The sequence of FeNi + Co + Cr + Al yielded a solid solution composed of 25 and 75% FCC and BCC, respectively, whereas AlNi + Co + Fe + Cr yielded a single-phase BCC due to the initial stable B2 structure of equiatomic AlNi which could not be destabilised by the addition of Co, Fe and Cr. They have later expanded for phase prediction using thermodynamic and kinetic principles, study of fundamental properties like diffusion, magnetism, their applicability

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Fig. 25 a XRD patterns and b TEM micrograph of equiatomic AlCrCuFeTiZn HEA obtained by MA for 20 h [174]

Fig. 26 Schematics showing a comparison of conventional versus sequential alloying [176]

as high-temperature coating material and their oxidation and corrosion behaviour and has produced several publications in the field. Panigrahi et al. [177] have also initiated studies on the HEAs by powder metallurgy route with the study of sintering mechanisms and have published several articles in the field. Srivastava et al. [178] studied the spray forming of HEA powders to realise its inherent rapid solidification effect and unique microstructural evolution mechanism. This study gives a new direction in understanding their solidification behaviour during layer-by-layer deposition of semi-solid/liquid droplets. An important contribution from Indian community has been in the area of diffusion in HEAs. Although sluggish diffusion has been perceived as a core effect in HEAs, studies by Vaidya et al. [179–181] have indicated that diffusion in HEAs cannot be considered as sluggish a priori. They have conducted diffusion studies in a quaternary CoCrFeNi and a quinary CoCrFeMnNi HEA at different temperatures ranging from 1073 to 1373 K by tracer technique using the 63 Ni isotope. The concentration profile

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Fig. 27 Comparison of Ni tracer diffusivity in low, medium and high entropy alloys plotted against a inverse absolute temperature and b inverse homologous temperature [179]

revealed that bulk and grain boundary diffusion mechanisms are dominant on the surface and at the interiors, respectively. The diffusivity in the quaternary HEA was lower when compared to the quinary HEA at absolute temperatures, whereas diffusion rates were higher when compared in terms of inverse homologous temperatures (Tm /T) (Fig. 27). These results showed that increased configuration entropy alone could not lead to sluggish diffusion [179–181]. On the other hand, the type and the nature of alloying elements play an important role in determining the rate of diffusion [180, 181]. Paul et al. [182, 183] have extensively studied diffusion-controlled growth of the phases and microstructural evolution in complex multicomponent materials. They have developed new experimental methods in multicomponent diffusion based on Onsager formalism. Another area where Indian scientists have significantly contributed is thermomechanical processing (TMP) of HEAs. At the initial stages of HEA research, a majority of the investigations focused on the microstructure and properties of as-cast alloys. Bhattacharjee et al. [184] pioneered the studies on microstructure, texture and properties of HEAs after thermo-mechanical processing by heavy deformation and annealing [98, 184–186]. They clarified for the first time that the quinary CoCrFeMnNi HEA could be heavily cold-rolled [184]. Further, the texture formation in the HEA showed pure metal to alloy/brass type texture transition, indicating the low SFE of the alloy [184, 187] which was later confirmed by other authors. The recrystallisation texture formation in the HEA showed retention of deformation texture components precluding the effects of strong preferential nucleation or growth on texture formation. The characteristic texture formation behaviour distinguished them from other low SFE alloys. The authors also investigated the effect of key parameters including grain size [188], imposed strain [185], temperature [189], alloy combination [190] and deformation paths [191] on microstructure and texture formation in the same HEA. Although first proposed by Lu et al. [128], Bhattacharjee et al. were the first to investigate the effect of thermo-mechanical processing on microstructure and

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properties of AlCoCrFeNi2.1 EHEA [192]. They showed that despite consisting of ordered L12 and B2 phases (Fig. 28), the EHEA could be heavily cold [192], cryo[193] or warm-rolled [194, 195] leading to many interesting phenomena including progressive disordering and nano-crystallisation of the L12 phase. However, the most remarkable results were that the evolution of a novel heterogeneous microstructure (Fig. 29) up on cryo-rolling and recrystallisation, leading to simultaneous enhancement in strength and ductility [193]. This heterogeneous microstructure can be further tuned to achieve extremely high strength (YS ~ 1900 MPa; UTS ~ 2000 MPa) with appreciable ductility (~8%) [196]. Sunkari et al. [197, 198] further studied

Fig. 28 a EBSD and b TEM micrographs of the AlCoCrFeNi2.1 EHEA. The associated SADPs in c and d (obtained from the green and red circles in (b)) confirm the presence of ordered L12 and B2 phases, respectively [192]

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Fig. 29 a Engineering stress–strain plot of the EHEA in different processing conditions; EBSD phase maps of b 90% cryo-rolled + 800 °C/h and c 90% cold-rolled + 800 °C/h EHEA [193]

the effect of TMP on the Laves phase containing HEAs. They have reported simultaneous improvement in mechanical properties guided by heterogeneous precipitation mediated heterogeneous nanostructure development in these materials. Samal et al. [199–201] studied the hot deformation behaviour of several eutectic HEAs. They have established the constitutive relation to understand the high temperature deformability at high temperature. Prediction of high temperature deformation behaviour is made using finite element simulation which is very much useful to understand the hot working capability of these materials for potential structural applications. Sourav et al. [202] established the process-structure–property relationships in hot forged AlxCoCrFeNi. They have proposed a modified rule of mixture to estimate the total strength of dual-phase HEAs. Nanoindentation behaviour of HEAs was studied by Ganji et al. [203, 204] to evaluate the contribution of different strengthening mechanisms on the mechanical properties. They have observed that major contribution in flow stress is due to Taylor hardening arising from dislocations intersection and grain boundary strengthening (GBS) arising from grain boundary-dislocation interactions. Biswas et al. have made important contributions in the areas related to phase stability in HEAs during sintering and solidification processing [163]. Their research includes the study of phase formation under non-equilibrium conditions in HEAs for understanding the phase selection and morphological evolution. An interesting work recently being carried out by them explored the possibility of developing better wear-resistant materials based on HEAs. They investigated the effect of soft dispersoid phases of Pb and Bi on the tribological properties of CuCrFeTiZn100-x Pbx and AlCrFeMnV100−x Bix [205] processed by MA and SPS, respectively. These materials

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Fig. 30 Wear rate as a function of varying load and increasing content of a Pb in CuCrFeTiZn100−x Pbx and b Bi in AlCrFeMnV100−x Bix [205]

are engineered to have soft dispersoids in the hard HEA matrix phase providing better wear resistance. A homogenous dispersion of the soft phase improved the boundary lubrication thereby improving the wear resistance of both materials (see Fig. 30). Abhaya et al. [206, 207] studied the effect of irradiation in HEAs with a potential application for nuclear reactors. The FCC FeCrCoNi remains structurally stable during irradiation and high temperature annealing. The evolution of defects during annealing is found to be dose dependant. Recently Srivastava and co-workers [208] reported the electrochemical water oxidation facilitated by graphene + FeCoNiCuCr HEA composites. These nanoparticles-based composites are prepared by mechanical milling of graphite-metal powders. They have the potential to replace noble metalbased electro catalysts thereby enabling new horizons in energy storage technologies. Aliyu et al. [209] developed high entropy alloy-graphene oxide composite coatings using electrodeposition with improved corrosion resistance. Ray et al. [210, 211] further studied the deformation and fracture behaviour of FCC and BCC HEAs. The deformation mechanism in FCC-based HEAs primarily involves dislocation–dislocation intersection, whereas BCC HEA is predominantly by Peierls–Nabarro barrier. Vikram et al. [212] recently studied the high-temperature mechanical behaviour of the additively manufactured (AM) eutectic high entropy alloys (EHEA) AlCoCrFeNi2.1 . Elemental powders are blended and fed into the system and deposits are prepared using laser engineered net shaping. Thermodynamic modelling of HEAs was performed to study the phase evolution and understanding the elemental partitioning. Guruvidyathri et al. [160, 213] studied the approach-based binary Gibbs energy-composition (G−x) plots to determine the phase evolution in HEAs. The study revealed that elements with smaller demixing tendency and weekly competing intermetallic phases in binary systems do not appear in HEA. Ghazi and Ravi [214] studied the effect of synthesis route on the phase stability using CALPHAD approach. Further Kumar et al. [215] studied the phase evolution in refractory alloys.

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HEAs have also attracted significant attention of several strong research groups at IIT BHU, IIT Kanpur, IIT Madras, University of Hyderabad, IIT Hyderabad, IIT Bombay and IISc Bangalore for understanding important aspects of HEAs including phase stability [216, 217], hot deformation [199, 200], HEAs development, mechanical behaviour [210, 211] and strengthening mechanisms [203, 204], creep and superplasticity [218]. The contributions of the Indian scientists are not only limited to HEAs but also extend to other HEMs. Gandhi et al. and Bhattacharya et al. have been actively pursuing the area of synthesis and properties of high entropy oxides [151, 219]. Recently, research on the development of high entropy materials for functional applications has been initiated [220]. Evidently, different research groups have worked on different aspects of HEAs to develop HEAs with superior properties, as summarised in Table 2 highlighting the major contributions of these research groups. In tune with the global trend, the number of publications in the areas of HEAs and HEMs has also been rapidly increasing in India (Fig. 31). The significant interest witnessed in the areas of HEAs and HEMs has resulted in a dedicated domestic conference series (International Workshop in High Entropy Materials or IWHEM) organised by IIT Madras (2015), IIT Hyderabad and HCU (2017) and recently by IIT Kanpur (2020).

13 Summary and Future Directions BMGs and HEAs constitute two of the most exotic classes of advanced alloys in recent times. These materials have a commonality in the form of their multicomponent nature. However, while the BMGs are not predominantly equiatomic in nature, majority of HEAs are equiatomic. In addition, most of the HEAs studied so far are crystalline in nature, while a few HEA BMGs have also been developed in recent times. BMGs have evolved earlier than HEAs and have been extensively investigated, attracting massive research interests due to their exotic structure and mechanical properties. The subsequent emergence of HEAs has given the impetus to investigate the massive composition space. In essence, both these classes of materials offer immense opportunities for developing novel alloys with advanced properties. The Indian scientists, as highlighted in this brief review, have substantially contributed towards the research and development of these materials. HEAs have a lot of future scope in various applications and a number attempts are being made to identify new applications for these exciting materials. One such development recently is the development of HEAs for biomedical applications [221]. These are called BioHEAs and their composition is tailored such that they will not contain bio-toxic elements. These are based upon equiatomic Ti–Nb–Ta–Zr–Mo HEA. Extensive research is needed to optimise the composition in order to ensure the biocompatibility and integrity of BioHEAs. As HEAs are multicomponent alloy systems, elemental segregation is highly likely during casting, which could lead to a heterogeneous elemental distribution that could adversely influence the applicability of BioHEAs. Additive manufacturing by selective laser melting can be a suitable

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Table 2 Indian Researchers and their Research Interests in HEAs Area of research

Research groups

Main contribution

MA, Powder Metallurgy and sintering mechanisms of HEAs

B. S. Murty, RS Kottada, IIT Madras K. Biswas, IIT Kanpur B. B. Panigrahi, IIT Hyderabad V. C. Srivastava, NML Jamshedpur

Nanocrystalline HEAs [174–176, 178] by MA, HEAs by sequential alloying, Spray forming of HEA powders

Refs.

Thermomechanical Processing of HEAs and Hot Compression of HEAs

P. P. Bhattacharjee, IIT Hyderabad K. Biswas and N. Gurao, IIT Kanpur G. Phanikumar and R.S. Kottada, IIT Madras

Microstructure, texture, and properties of HEAs, Simultaneous enhancement in strength and ductility in EHEA

[184, 193]

Phase stability and K. Biswas, IIT Kanpur mechanical behaviour of N. K. Mukhopadhyay, HEAs IIT BHU P. P. Bhattacharjee, IIT Hyderabad K. Rajulapati, Uni. of Hyderabad K. R. Ravi, IIT Jodhpur

Soft dispersoids in the hard HEA matrix for better wear resistance, Strengthening mechanisms using Nanoindentation, Role of synthesis route on phase evolution

[203, 205, 214]

Diffusion in HEAs

B. S. Murty, IIT Madras Aloke Paul, IISc Bangalore K. Kulkarni, IIT Kanpur

Role of alloying elements on the diffusivities, new experimental methods in multicomponent diffusion based on Onsager formalism

[179, 182, 183]

Creep and Superplasticity of HEAs

A. H. Chokshi, IISc Evidence of Bangalore superplasticity in R. S. Kottada, IIT Madras Cantor alloy using conventional treatments

[218]

High entropy oxides and High Entropy ceramics

A. S. Gandhi, IIT Bombay S. S. Bhattacharya, IIT Madras

Multicomponent rare earth oxide (REO) nanocrystalline high entropy oxides

[151, 219]

High entropy functional materials

B. S. Murty, IIT Madras K. Biswas, IIT Kanpur

Half-huesler based [220] Ti2 NiCoSnSb HEA for thermoelectric applications

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Fig. 31 Year-wise International publications in the field of HEAs by the Indian researchers

method for suppressing elemental segregation. Extensive work needs to be taken up for the development and manufacturing of BioHEAs in India.

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Refractories as Advanced Structural Materials for High Temperature Processing Industries Arup Ghosh, Somnath Sinhamahapatra, and Himansu Sekhar Tripathi

Abbreviations MOR MOE C2 S C3 S C4 AF BN SIALON MgO–C Mag–Al AZS

Modulus of Rupture Modulus of Elasticity Di Calcium Silicate Tri Calcium Silicate Tetra Calcium Alumino ferrite Boron Nitride Silicon Aluminium oxynitride Magnesia Carbon Magnesium Aluminate Spinel Alumina Zirconia Silica

1 Introduction Refractories are used as high temperature materials for structural applications in various industries. These are applied as lining materials in high temperature vessels used in industries such as ferrous and non-ferrous metallurgy, cement, glass and ceramics, and petrochemicals. In India, out of the total refractory consumed, more than 70% of refractories are used in steel, 7% in cement, 5% in non-ferrous metallurgy, 5% in glass and the rest in other industries. Refractory systems mostly comprise different oxides depending on its applications (Table 1). Carbon is also used as oxide– carbon composite refractory in several steelmaking areas. In the present review paper, A. Ghosh (B) · S. Sinhamahapatra · H. S. Tripathi CSIR-Central Glass & Ceramic Research Institute, 196, Raja S. C. Mullick Road, Kolkata – 32, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 D. Bhattacharjee and S. Chakrabarti (eds.), Future Landscape of Structural Materials in India, https://doi.org/10.1007/978-981-16-8523-1_11

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280 Table 1 Refractory compounds for different application areas

A. Ghosh et al. Systems

Applications

SiO2

Glass Coke oven

ZrO2 –Al2 O3 –SiO2

Glass Continuous casting of steel

MgO–CaO

Steel making (Primary, Secondary)

MgO–Al2 O3 –SiO2

Steel ladles

Al2 O3 –SiO2

Iron making, Coke oven batteries, Heat treatment furnaces, Aluminium Whiteware industries

MgO–Cr2 O3

Copper, Steel, Cement

focus will be concentrated on current refractory practice in steel-making and other major application areas along with future scope of development.

2 Refractories for Primary Steelmaking Refractory technology has developed simultaneously with the advancements in iron and steel making technology. The demand for superior quality clean steel has changed the primary and secondary steelmaking technology along with casting process. This necessitated the change in refractory quality/properties for different applications to withstand the severe operating conditions. The stabilisation of steel production made it imperative to improve the lining life of reaction vessels through selection of suitable refractory. MgO and CaO are being used for a long time as refractories for primary steelmaking processes due to the basic environment prevailing in the vessels. However, with the changes adopted from time to time in steelmaking process as well as the operating condition of vessels, the refractory product quality changes. Dolomite (CaO.MgO) refractory was earlier used as fettling material for the hearth of Bessemer converters [1]. Sintered dolomite tends to hydrate in contact with atmospheric moisture due to the presence of the predominant CaO phase. This problem is less pronounced in stabilised dolomite, which is produced by reaction of dolomite with silica or iron oxide materials [2]. The main phases formed due to these reactions are periclase (MgO), tri-calcium silicate (3CaO.SiO2 ) and di-calcium silicate (2CaO.SiO2 ). These bricks were used in sub-hearth of furnaces, side walls and ladles. The introduction of basic oxygen process of steelmaking (LD Converter) made the operating condition more severe with a tapping temperature ranged between 1650° to 1720 °C and slag with CaO:SiO2 :: 3:1. This demanded development of highly dense and corrosion resistant sintered dolomite. This is essential not only to resist hydration but also to hinder the slag infiltration and corrosion against the refractory [3, 4]. The densification of purer varieties of dolomite needs high sintering temperature, due

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to its high refractoriness. High density sintered dolomite (3.20–3.30 g/cm3 ) can be produced either through single step process at 1900 °C in shaft or rotary kiln or by two stage calcination process at 1000 °C and 1600 °C respectively. High density sintered dolomite grains are required to produce dolomite refractory with low rate of wear against basic slag. Originally, the LD converter was lined with pitch/tar bonded dolomite/magnesite refractories [5]. Thereafter, with the invention of high performance MgO–C refractory, the converters were lined only with this refractory. It was established that, in the furnace environment comprising highly basic slag, MgO–C refractory was the best option to increase the lining life. The average lining life of BOF converters improved dramatically from 200–300 heats to 5000–7000 heats with the introduction of MgO–C refractory along with periodical gunning and slag splashing in the lining. The innovation of MgO–C products in steelmaking received lots of R&D attention, the variables being quality of MgO, graphite, metal additives, binders, etc. The enhancement of properties was with respect to hot strength, resistance to oxidation, slag attack, thermal shock resistance, thermal conductivity, modulus of elasticity etc. The addition of different metal powders (Al, Si, Mg, Al–Mg) to MgO–C system showed superior oxidation resistance and increase in hot strength [6]. Metals are added due to their higher affinity to oxygen than that of carbon, at the critical temperature range. Therefore, the carbides and nitrides, formed with the metallic antioxidants, protect the graphite against oxidation. Additionally, the presence of antioxidants improves the high temperature strength in air and under reducing atmospheres. High amount of graphite increases the heat loss due to its high thermal conductivity and causes high carbon pickup by the molten steel as well. In addition to this, release of carbon dioxide during different heat treatment of refractory causes environmental pollution. Researchers are trying to reduce the carbon content of MgO–C refractory for reducing thermal conductivity, without compromising its critical thermo-mechanical and chemical properties. This can be done by making the structure denser, by using carbon black nanoparticles [7]. Research is also going on to develop in-situ carbon nanotube in the matrix through catalytic pyrolysis of organic binder used in the refractory. Properties of MgO–C refractories with and without nano-carbon are given in Table 2 [8]. Incorporation of nano-carbon black improves the physical and thermomechanical properties of MgO–C refractory to that of conventional MgO–C refractory. The homogeneous mixing of nano-carbon can be obtained, if it is dispersed in suitable liquid medium during the mixing process. However, intensive dry mixing process of nano-carbon with finer aggregates is also followed in a suitable counter current mixer. It is also noticed that, for nano-carbon bonded MgO–C refractory, the MOE is much less compared to that of conventional MgO–C refractory. The lower MOE value of nano-carbon bonded MgO–C refractory indicates that the addition of nanocarbon helps reduce the stress generation, which increases its flexibility and thermal shock resistance than conventional MgO–C refractory. The addition of nano-carbon develops submicron size pores.

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Table 2 Properties of MgO–C bricks with and without nano-carbon [8] Properties

10% carbon containing conventional MgO–C refractory

0.9% Nano C + 3% graphite containing MgO–C refractory

Apparent porosity (%)

3.3

5.2

Bulk density (g/cm3 )

3.03

3.05

Cold Crushing Strength (MPa)

37.5

59

Hot MOR at 1400 °C (MPa)

2.3

3.7

Modulus of Elasticity (GPa) [MOE]

76

71

Thermal Conductivity at 1000 °C 9.3 (W/m°K)

6.4

in the matrix, which is responsible for lower MOE value of nano-carbon added bricks compared to graphite added samples. Using nano-carbon improves Hot MOR due to better densification and less oxidation of carbon. Finally, the higher thermal shock resistance is related to the lower residual fracture energy of nano-carbon added bricks. Use of nano-carbon black also reduces total carbon content thus reducing heat loss and thermal stress to the steel shell. It was also reported [9] that, compared to conventional MgO–C bricks (with 20% flake graphite), bricks containing 3 wt.% carbon black (50 nm size) showed similar thermal shock, but lower, thermal conductivity, wear and oxidation rates. Carbon black forms whiskers with antioxidants, fills the pores and increases the toughness. The oxidation of nano-carbon generates small pores, which resist slag infiltration and thereafter wear.

3 Refractories for Secondary Steelmaking After the conventional refining, the final or secondary refining is carried out, which include vacuum degassing by RH to remove hydrogen from steel, VOD, AOD, Ladle Furnace etc. Refractories for secondary refining process must withstand the vacuum condition of the furnace. Magnesia chrome was long being used for this application. However, the latest trend is to use magnesia-carbon and alumina spinel castable [10]. The snorkel portion of RH degasser is lined with bricks in inner wall and alumina spinel monolithic in the outer lining.

3.1 Refractory for Stainless Steel Making (AOD Converter) Stainless steel is manufactured in AOD converters, which operates in the range of 1700° to 1740 °C. The refractory wear is caused by erosion of molten metal, gas turbulence in the vessel and slag of basicity (CaO:SiO2 ) of 1.5 to 2.0. To withstand

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Fig. 1 Refractory lining in AOD converter [12]

these conditions, the refractory should possess high refractoriness under load (RUL), volume stability and thermal shock resistance [11]. Dolomite, a thermodynamically stable material, is suitable for this condition. The zone-wise lining concept is adopted in AOD converter due to different atmospheres prevailing in zones during operations (Fig. 1). Maximum wear occurs in the tuyere and belly area, where fired Magnesiaenriched Dolomite is used due to its better corrosion property. The bottom and top cone area is lined with pitch or resin-bonded or fired dolomite bricks, which has better thermal shock resistance. The properties of the refractory in different zones are listed in Table 3.

3.2 Refractory for Secondary Steel Ladles Conventionally ladles were lined with alumina-silicate bricks. With the introduction of secondary refining concept, it was lined with zircon (ZrSiO4 ) bricks. The stringent operating conditions in secondary metallurgy require continuous improvement and innovations in the refractory linings to economically enhance the lining life. The

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Table 3 Typical properties of dolomite bricks for AOD converter [11] Properties

Tuyere area

Belly portion

Top cone

MgO content (%)

63.2

62.5

57.2

42.1

CaO content (%)

34.8

35.7

40.8

55.7

Apparent porosity (%)

14.0

14.0

14.5

14.0

2.90

2.90

2.88

2.85

Bulk density (g/cm3 ) Cold crushing strength

(kg/cm2 )

Refractoriness under load (ta °C)

600

680

610

600

>1700

>1700

>1700

>1700

refining process to produce ultra-low carbon steel consists of different steps like deoxidising, de-gassing, de-sulphurisation and de-carburisation (Fig. 2). The factors, which degrade the refractory performance, are thermal shock, abrasion, slag corrosion and oxidation, as shown in Fig. 3 [13]. For oxide cleanliness in steel, the refractory materials should have low oxygen potential against aluminium dissolved in steel to avoid re-oxidation. Silica-based high alumina materials like andalusite (Al2 O3 .SiO2 ), bauxite and magnesite-chrome and zircon are susceptible to reduction by aluminium and hence, are not suitable. Best result, as defined by low level of oxidation, is obtained with dolomite, magnesia and alumina. Due to higher carbon level in MgO–C bricks, the carbon pickup in steel is higher. As a result, for producing low carbon clean steel, MgO–C bricks are not used in the metal zone and bottom. Moreover, due to the higher conductivity of carbon in Fig. 2 Secondary steel refining ladle [13]

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Fig. 3 Factors responsible for refractory wear in ladles [13]

Table 4 Properties of ladle refractories [15] Properties

MgO–C bricks

Al2 O3 –MgO–C bricks

Al2 O3 –MgAl2 O4 Refractories Fired bricks

Castable

Carbon content (%)

10–15

5–8

–

–

Thermal conductivity, (W/m°K)

10

6.4

3.5

3.5

Bulk density (g/cm3 )

2.9

3.25

3.0–3.2

2.9–3.0

MgO–C bricks (10–15% C), the temperature loss is 10–15 °C higher compared to Al2 O3 –MgO–C brick (5– 8% C) and Al2 O3 -Spinel brick / castables [14]. Typical properties of these bricks are given in Table 4. On the other hand, alumina-magnesia refractory, by nature, differs significantly from alumina-spinel refractory. Alumina magnesia brick expands up to 1400 °C due to mag-al spinel formation, thus making the structure dense, which hinders slag penetration. Therefore, this brick is less prone to wear and structural spalling than alumina-spinel refractory [7].

4 Refractories for Continuous Casting High quality continuous casting refractories are essential for manufacturing low carbon steel. Figure 4 describes the continuous casting of steel and the refractories used in this system [16]. The slide gate refractories include the plate and the nozzle, which control the flow rate of molten steel. Its life depends on the kind of steel, casting time, temperature and throughput. Normally, resin-bonded Al2 O3 –C or ZrO2 –C refractories are used in this system. Ladle shroud is connected in the slide gate. It is used for pouring the molten steel to tundish, preventing any exposure to

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Fig. 4 Refractories components used in the continuous casting of steel [16]

air. Alumina-graphite compositions are mainly used for this purpose. The submerged entry nozzle (SEN) and stopper are connected between tundish and mould, which are also made of metal-bonded alumina carbon material. The refractories for nozzles need to control the oxidation of steel. Air enters through the joints between the nozzle and the slide gate and deteriorates the steel quality. Therefore, a nozzle design is made to pass argon (Ar) in acounter-current flow, sealing the refractory from air contact (Fig. 5). In the functional refractory components like slide gate plate, SEN, shroud, the carbon pickup from refractory is a problem. Non-oxide materials like Si3 N4 , SiAlON, BN etc. possess excellent thermo-mechanical properties, non-wetting characteristics, corrosion property and better oxidation resistance compared to carbon. Some preliminary comparative evaluation on Al2 O3 –C and Al2 O3 –SiAlON/AlON products are given in Table 5, which reveals the superior properties of oxide-non-oxide system. Therefore, oxide-non-oxide refractory is a potential futuristic refractory material for functional application.

5 Refractories for Non-Ferrous (Copper and Lead) Industry Refractories for copper and lead smelting furnaces are subjected to severe atmosphere of fayalitic (2FeO.SiO2 ) slag, which is acidic, low viscous and low melting [17]. Temperature in the shaft area for copper is 1250 °C and below 1200 °C for lead. Magnesia chromite bricks are the standard products for lining in the contact areas of

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Fig. 5 SEN equipped with gas bubbling system for sealing the refractories [16]

Table 5 Properties of oxide–carbon and oxide-non-oxide refractories

Properties

Al2 O3 –C

Al2 O3 –SiAlON/AlON

Al2 O3 content (%)

80–85

72–78

Carbon (%)

7–8

4–5

Crushing strength (MPa) 150

170

Hot MOR at 1400 °C (MPa)

18–23

18–23

Residual strength after thermal shock, (Water cooled 5 times) ( %)

30–40

45–55

slag and molten metal in the furnaces in these industries. Corrosion is the main cause of wear in this furnace due to acidic character of slag and its low viscosity. Chromite (Mg, Fe) (Cr, Al, Fe)2 O4 contained in the refractory reacts with the metallic melt and slag to form complex spinel, where Zn, Ni and Cu are absorbed in the chromite lattice. Mainly three types of magnesia chromite bricks are available, viz. silicate bonded, direct bonded and fused/re-bonded [18]. Silicate-bonded bricks possess poor thermo mechanical properties and low corrosion resistance, so are not suitable in the slag/molten metal zone (Table 6). Direct bonded bricks have good thermal shock resistance and moderate corrosion resistance, whereas re-bonded/fused products are excellent in corrosion resistance due to larger crystallite size of MgO and Chromite (Table 7). Chrome-based refractory contains chromium in hexavalent state, which forms soluble and toxic di-chromates of potassium and sodium. Therefore, extensive

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Table 6 Comparative properties of different Magnesite Chrome bricks Properties

Silicate bonded

Direct bonded

Re-bonded/Fused

Corrosion resistance

Poor

Good

Excellent

Hot abrasion resistance

Poor

Good

Excellent

Thermal shock resistance

Excellent

Moderate

Poor

Cost

Low

Moderate

High

Table 7 Typical properties Magnesia Chrome bricks [19] MgO

Cr2 O3

SiO2

BD, g/cm3

A.P., %

CCS, MPa

Hot MOR at 1400 °C, MPa

62.8

15.8

1.6

3.09

17.0

35

4.5

research is going on to develop chrome-free refractory, which can resist fayalitic slag corrosion. Some products based on MgO–MgAl2 O4 and MgO–ZrSiO4 have been developed, but these bricks are not at all comparable with Mag-Chrome with respect to non-ferrous slag corrosion.

6 Refractories for Cement Kilns Portland cement is mainly produced in rotary kilns, the main raw materials being limestone, clay, silica sand and iron-containing materials. The blended materials are sintered around 1450 °C to generate cement clinker. Cement rotary kilns have normally 5 zones, (i) preheating, (ii) decomposition, (iii) transition, (iv) burning, and (v) cooling, out of which the transition and burning zones are the most vulnerable for the refractory [20]. The temperature and processing functions of each zone are illustrated in Table 8. The operating factors affecting refractory performance are abrasion from kiln feed, chemical reaction, thermal gradients and mechanical stress. Low elastic modulus is another requirement due to kiln rotation. During the rotation of kiln the bricks are subjected to compressive stress of raw materials load when the lining is in down Table 8 Temperature and process functions of different zones of a cement rotary kiln Different zones

Operating Temp (°C)

Physico-chemical processes

Preheating

Cold FEG (a smaller number is considered as superior in the comparison of resolution). In the SEM equipped with FEG source, a resolution of ~1 nm can be obtained for a standard sample under optimum condition, whereas the resolution is worse (~10 nm) in case of the electron emitters involving thermionic emission. In recent years, the subnanometre resolution has been also achieved in the SEMs having FEG sources using optimum imaging conditions, including beam alignment, astigmatism correction,

Fig. 1 Optical microscope image of microstructure of MoSi2 processed by a reaction hot pressing of elemental Mo and Si powders, and b hot pressing of commercially available MoSi2 powders; recorded using plane-polarized illumination [11]. The arrow in (b) shows dispersed SiO2 particles (present as impurity) with high reflectivity, appearing bright in plane- polarized light. Reprinted by permission from Springer Nature

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small working distance, optimum objective aperture and contamination-free conductive sample. Recently, SEMs with facilities for beam-deceleration and charge neutralization have come up to minimize charging during the observation of non-conductive samples. In the transmission electron microscope (TEM) operated in conventional mode using an objective aperture, the obtained images exhibit contrast due to the variations in the amplitude of transmitted or diffracted electron waves after they pass through the electron transparent part of a 3 mm diameter thin foil sample [1, 3, 4]. Additionally, high resolution TEM involving phase contrast imaging is used to examine various structural defects, grain boundaries and interfaces with details finer than 0.2 nm. During the last decade, the image resolution has been significantly improved further to ≤ 0.1 nm by adopting advanced technology for correction of the spherical aberration of the objective lens, which has facilitated the observation of the structure of complex materials at atomic resolution, particularly 2D materials (graphene, MoS2 , etc.) much beyond the limit possible through other techniques. The TEM specimen holders are designed to carry out in-situ dynamic experiments involving heating, cooling and straining of specimens along with limited tilting, capturing of still and video images with selected area electron diffraction patterns. The experiments involve in-situ dynamic study of the microstructural variations with change in temperature or tensile straining, so that it is possible to examine the mechanisms phase transformations or plastic deformation, respectively [12–14]. Preparation of the thin foils for observation in the TEM has been always considered challenging by the researchers, particularly the materials with heterogeneous microstructures, which undergo differential thinning. In the last two decades, a dual-beam focused ion-beam (FIB) microscope has been developed, where 1 μm thick lamellae are cut from Pt-coated selected locations of bulk samples by milling with Ga ions, which are subsequently lifted out by using suitable automated micromanipulator, mounted on the grid (3 mm diameter half ring), and then thinned to electron transparency for observation using a TEM. In this manner, site-specific sample preparation is carried out from a heterogeneous sample, or a layered thin film or coating [1]. The secondary electron image (Fig. 2) of the cross-section of a Ptcoated typical lamella prepared by FIB shows an interfacial layer of pyrolytic carbon (Py C) in the C-fibre-SiC composite [15]. The C-fibre is coated with Py C to weaken the interface to promote interfacial debonding, leading to an increase in the crack path tortuosity along with a typical damage tolerant behaviour. High resolution imaging and diffraction in TEM along with in-situ experiments and advanced sample preparation facilities have facilitated the in-depth understanding of the structure of materials, internal interfaces as well as mechanisms of phase transformation and deformation or functional behaviour at multiple length scales (atomic, nano- and micro-). The major limitations are the artefacts caused by sample preparation, effect of surface, and very small area of observation. The area being observed may not represent the bulk. However, for the samples wellcharacterized by XRD and SEM, the use of TEM provides a vista to obtain a deeper understanding of the structural details, as mentioned above.

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Fig. 2 Secondary electron image of a Pt-coated TEM lamella prepared by FIB to examine the fibre-matrix interface containing a layer of pyrolytic carbon (Py C) in a carbon fibre-SiC composite processed chemical vapour infiltration [15]

2.3 Measurement of Grain/Crystallite Size, as Well as Volume Fraction and Distribution of Phases Considering a strong influence on the mechanical behaviour of materials, it is often necessary to make an accurate assessment of the grain size. It is possible to resolve and measure by optical microscopy an average grain size of ≥5 μm, whereas FEGSEM or TEM can be used for examining the details of much finer sub-micrometer size grains. For powders, thin films and bulk materials having grain sizes in the nanocrystalline regime (≤100 nm), the broadening of XRD peaks is analysed by using various approaches including the Scherer formula, Williamson–Hall relation and Warren–Averbach method as well as their modified versions [2, 16–19]. Besides the grain size, micro-strain can also be estimated by analysing peak broadening using Williamson–Hall analysis [17]. For such analyses, it is necessary to subtract the contribution of instrumental broadening from the full-width half maximum (FWHM) of the XRD peaks. Since the size of the smallest coherently diffracting domain is measured by XRD analyses, the results are affected by the presence of twin boundaries, dislocations and stacking faults, which are known to contribute to peak widening. Therefore, it is found necessary to verify the obtained results through dark-field TEM examination [20–23]. It has been noticed that the agreement between the results of XRD analyses and TEM is greater if the grain size distribution is narrow. In multiphase alloys, it is necessary to determine the volume fractions of the constituent phases in multiphase alloys and that of reinforcements in the composites. The measurement of volume fractions is carried out by image analysis of the microstructures observed or recorded in the optical microscope or SEM by two methods: (i) calculation of area fractions of the constituent phases by considering the grey scale varying with contrast; and (ii) point counting. In nanocomposite thin films or multiphase intermetallic alloys having phases in the microstructure, which cannot be differentiated on the basis of contrast during observation in optical or

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SEM, Rietveld analysis of the XRD peaks from the constituent phases is used to determine the phase volume fractions [20, 24]. The results of the Rietveld analysis are considered as acceptable, provided the goodness of fit values calculated using a statistical model (chi-squared) are found to lie between 1 and 2. This method however has limitations, because the XRD peaks are well-distinguishable only if the volume fraction is reasonably high (≥ 5 vol%), and there could be overlapping between the XRD peaks from various phases. In some of the recent studies, the distribution of dispersed phase or particles has been quantified by the multi-scalar analysis of area fractions in multiple SEM backscattered electron images of microstructures to determine the homogeneous length scales, which is reported to be inversely proportional to the uniformity of distribution [25–28]. The homogeneous length scale (LH ) is defined as the length such that any area greater than LH 2 can be considered to have a ‘homogeneous’ distribution of particles. For analysis, a MATLAB- based computer programme was used, where the SEM images (converted into binary images) were used as inputs.

2.4 Observation of Dislocations, Stacking Faults and Twins It has been possible to estimate the density of dislocations, stacking faults and twins in nanocrystalline samples by analysing XRD peaks using the modified Warren– Averbach analysis [19]. However, direct observation of the aforementioned line and surface defects is possible and can be routinely carried out by a TEM. Furthermore, the Burgers vector of perfect or partial dislocations, the line direction as well as the slip plane are accurately determined by bright-field and dark-field imaging in the TEM. For this purpose, the invisibility criterion involving electron diffraction and dark-field TEM is used to determine the Burgers vector. The dislocation substructure formed in pure metals, alloys and metallic matrices of composites during thermomechanical processing, or deformation by creep, fatigue or wear has been widely reported in the literature. The formation of dislocation networks in metals, alloys and intermetallics with varied crystal structures has been similarly analysed to understand the dislocation reactions and strengthening mechanisms. The addition of various alloying elements is a well-accepted strategy for enhancing the ductility of the brittle intermetallics by the alteration of crystal structure, antiphase boundary energy or stacking fault energy. An increase in the ductility often involves the activation of fresh slip systems, which is confirmed by extensive TEM studies. In a similar way, the presence of superlattice intrinsic stacking faults and antiphase boundaries has been investigated by TEM. Often, the weak-beam-based high resolution dark-field TEM imaging is employed for estimating the location and width of dislocation core [29, 30]. The weak-beam dark-field technique has been also effectively used to reveal the misfit dislocations and localized strain contrast at the low angle grain boundaries or semi-coherent interphase interfaces [31].

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2.5 Analysis of Preferred Orientation and Imaging of Orientation Distribution Thermomechanical processing of metals and alloys is often carried out to obtain a refined microstructure along with preferred crystallographic orientations (texture) as well as local lattice misorientations (micro-texture), which need to be quantified to examine their effect on mechanical properties and environmental degradation. The preferred crystallographic orientation is also found in directionally solidified single crystals or eutectic alloys. Such crystallographic textures lead to anisotropic mechanical properties, including elastic modulus, hardness and yield strength, as well as fatigue and creep resistance. The crystallographic texture is routinely evaluated by using X-ray diffractometers equipped with a texture goniometer. The orientation of grains with respect to the electron beam direction and relative misorientation between selected grains as well as the parts of a single grain (i.e. the subgrains) is determined in a TEM by analysing the Kikuchi line patterns. One disadvantage of the method used for the evaluation of grain orientation by the analysis of Kikuchi patterns in a TEM is that only a small area of the specimen can be observed, and specimen preparation artefacts can affect the results. Further, because of the requirement of inelastic scattering, the Kikuchi patterns are generated only at slightly thicker regions of the specimen. In spite of such limitations, quantification of the Kikuchi patterns obtained through the TEM has been used to examine local lattice misorientations [32]. In recent years, the precession electron diffraction (also referred to as nano-beam diffraction, NBD) has evolved as a reliable technique to map orientations on a nanometric scale [33]. Similar to the phenomenon observed in the TEM, the Kikuchi patterns are generated by diffraction of the backscattered electrons in the SEM. This technique is known as the electron backscattered diffraction (EBSD) and is employed for the imaging of orientation distributions of grains or within a grain [34]. Besides identifying the angles of misorientation between the sub-grains, the EBSD has been often used to identify various constituent phases in the SEM-obtained microstructures [35], map the strain distribution [36], as well as to distinguish the special boundaries of low energy based on the coincidence site lattice [37]. While it is well-established that the mechanical properties of an alloy are strongly influenced by the prior micro-texture, it may also be noted that the misorientation distribution evolves and may change significantly during deformation. The EBSD technique has been used extensively to examine the grain misorientation distribution evolving after deformation by creep, fatigue or wear or to identify the preferred cleavage planes in the process of fracture [38–41]. In recent years, the transmission Kikuchi diffraction (TKD) has emerged as a standard technique, where a thin electron transparent sample (transparent at an acceleration voltage of 30 kV in SEM) is subjected to EBSD analyses. Compared to the conventional EBSD, the interaction volume is reduced as a thin sample is used, and therefore the lateral resolution is reduced to