Abstracts Book

Preface

High entropy alloys (HEAs) are multicomponent equiatomic or near equiatomic alloys. They have high configurational entropy due to which they tend to form solid solutions with simple crystal structures. Prof. S. Ranganathan is the first to mention about these alloys in open literature in his paper on “Multimetallic cocktails” published in 2003. Prof. J.W. Yeh has been working on these alloys since 1995, but the first journal publication from his group on these exciting alloys appeared in 2004. Interestingly, Prof. B. Cantor has also been independently working on these alloys since 1981, but published his work in a journal only in 2004. In the last decade there have been a lot of reports in this field including a recent book of Elsevier by B.S. Murty, J.W. Yeh and S. Ranganathan.

There are a number of fundamental issues that need to be understood in these materials, such as phase selection, lattice distortion, microstructure, thermal stability, deformation behavior, diffusion, thermodynamic properties, processing challenges, etc. Though there is increasing number of reports indicating some interesting properties of these materials, a complete evaluation of the wide spectrum of properties of these materials is essential before their potential for various applications can be established.

Globally there is an initiative to start a consortium for understanding these materials in the form of Centre for Complex Concentrated Alloys (C3A). In India, there are only a few groups working in this area. Capabilities exist in the country in the areas of first principle calculations, MD simulations, thermodynamics, phase field modeling, synthesis, processing, characterization, property evaluation and component development. There is a need to bring to these people together in order for the country to make significant contributions in this field.

This workshop has been successful in bringing together scientists with expertise ranging from first principle calculations to processing and applications, so that they look at the issues that need to be addressed and the direction that should be taken in the coming decade in order to not only arrive at a better fundamental understanding but also develop a few possible applications of these alloys. This is the first meeting on HEAs in India.

We are grateful to all the participants who have come enthusiastically from long distances to participate in this workshop. Our special thanks to overseas participants, Prof. J.W. Yeh, Prof. Chris Berndt, Prof. Rajiv Mishra and Dr. Dan Miracle for the value they gave to this workshop. We are grateful to Prof. Brian Cantor for taking his precious time out and giving a video message for the participants of the workshop.

We are grateful to Boeing for being the main sponsor for this workshop. We are also thankful to Department of Science and Technology, Defence Research & Development Organisation, Government of India, GE, Anton Paar and Hysitron for their wholehearted support to the event.

We are confident that this workshop will be an enriching experience to every participant.

M Kamaraj, BS Murty, Ravi Sankar Kottada KC Hari Kumar, Srinivasa Rao Bakshi

National Workshop on High Entropy Alloys: Prospects and Challenges

Organised by Department of Metallurgical and Materials Engineering, IIT Madras in association with Boeing

March 28-29, 2015, IC&SR Auditorium, IIT Madras

Programme

March 28, 2015

08.30 Registration 09.00 Inaugural Session  Welcome: KC Hari Kumar, HOD In-charge, Dept. of MME, IITM  Welcome Remarks: Bala K Bharadvaj, Boeing India  Introduction to the workshop: BS Murty, IIT Madras  Presidential Remarks: S Ranganathan, IISc Bangalore  Inaugural Address: JW Yeh, NTHU Taiwan Physical metallurgy of high-entropy alloys  Video Message by Brian Cantor, Bradford University, UK.  Vote of Thanks: Ravi Sankar Kottada, IIT Madras 10.00 Session 1: Basics Chair: R Krishnan, Bangalore 10.00 S Ranganathan, IISc Bangalore Solid Solutions - their limits and extensions 10.15 D Miracle, US Air Force Base, USA Accelerated discovery and development of multi-principle element alloys via ICME 10.30 Rajiv Mishra, University of North Texas, USA Some observations on unique aspects of mechanical behavior of high entropy alloys 10.45 Tea Break 11.15 Session 2: Basics II Chair: Rajiv Mishra, University of North Texas, USA 11.15 BS Murty, IIT Madras Excitement and challenges in the field of high entropy alloys 11.30 Chris Berndt, Swinburne Uni., Australia Thermal spray routes towards achieving high entropy alloy phase structures 11.45 KC Harikumar, IIT Madras Challenges in thermodynamic modelling of multicomponent systems 12.00 Lunch 13.00 Session 3: Synthesis & Processing Chair: NK Mukhopadhyay, IITBHU, Varanasi 13.00 A Subramanian, IIT Kanpur Orientational high entropy alloys

13.15 SR Bakshi, IIT Madras Effect of thermo-mechanical processing on NiTiCuFe multicomponent alloys 13.30 Pinaki Bhattacharjee, IIT Hyderabad Thermo-mechanical processing of FCC CoCrFeMnNi high entropy alloy 13.45 Discussion on Session Topics Moderator: AH Chokshi, IISc Bangalore 16.15 Tea Break 16.45 Poster Session 18.00 Departure for Dinner Venue

March 29, 2015

09.00 Session 4: Characterization, Properties & Applications Chair: Chris Berndt, Swinburne Uni., Australia 09.00 R Krishnan, Bangalore HEAs for AUSC plants, radiation environment and gas turbine engines 09.15 James D Cotton, Boeing Research & Technology, Seattle, USA High entropy alloys: potential for airframe applications 09.30 KG Pradeep, RWTH Aachen, Germany High entropy alloys to massive solid solution alloys: trend in complex alloy design 09.45 Joysurya Basu, IGCAR, Kalpakkam Analytical microscopy for understanding structure and chemistry of multicomponent alloys 10.00 R Koteswara Rao, Univ. of Hyderabad Structural details, phase stability and mechanical properties of microcrystalline and nanocrystalline Ti-Ni-Cr-Co-Fe high entropy alloy 10.15 S Abhaya, IGCAR Kalpakkam High entropy alloys: Probing defects using positrons 10.30 Tea Break 11.00 Session 5: Characterization, Properties & Applications Chair: VS Raja, IIT Bombay 11.00 Ravi Sankar Kottada, IIT Madras Thermal stability and mechanical behaviour of high entropy alloys (HEA) synthesized by mechanical alloying and spark plasma sintering 11.15 Vinod Kumar, MNIT Jaipur Synthesis and characterization of light weight high entropy alloys 11.30 K Biswas, IIT Kanpur High entropy alloys: pertinent issues on processing and stability 11.45 K Siva Prasad, NIT Trichy Studies on CNT reinforced nanocrystalline AlCrCuFeNiZn high entropy alloy composite 12.00 Lunch 13.00 Session 6: Modelling & Simulation Chair: Umesh Waghmare, JNCASR, Bangalore 13.00 G Phanikumar, IIT Madras Challenges in extending IRF concept in the solidification of multicomponent alloys 13.15 Sankara Subramanian, DMRL, Hyderabad Challenges in the atomistic modeling of multicomponent alloys

13.30 Abhik Chowdhury, IISc Bangalore Microstructure evolution in multi-phase, multi-component alloys 13.45 Jatin Bhatt, VNIT Nagpur Thermodynamic modeling for predicting metallic glass formation in high entropy alloys 14.00 Tea Break 14.30 Discussion on Session Topics Chair: KC Hari Kumar, IIT Madras 16.00 Way Forward & Conclusion Chair: S Ranganathan, IISc Bangalore

Poster Session

S.No Name 1. Ameey Anupam, IIT Madras Microstructural characterization of plasma sprayed high entropy alloy coatings 2. S Praveen, IIT Madras Phase evolution, densification, and compressive properties of high entropy alloys 3. R Lavanya, IIT Madras Alloying and phase evolution in refractory CrMoNbTiW high entropy alloy 4. Satish Idury, VNIT Nagpur Design of high entropy metallic glass compositions from invariant reactions predicted by CALPHAD methods through PHSS parameter 5. Anoop K, IIT Madras Carbide formation during synthesis of Co-Cu-Fe-Mn-Ni-W multicomponent alloys by mechanical alloying and spark plasma sintering route 6. Nandhini Singh, IIT BHU Synthesis and characterization of FeAlZnCrCuMgSi and FeAlZnCrCuMgMn high entropy alloys by mechanical alloying 7. Vikas Shivam, IIT BHU Synthesis and characterization of Fe-Al-Zn-Cr-Cu-Mg and Fe-Al-Zn-Cr-Cu-Mg-Co high entropy alloys by high energy ball milling 8. Tazuddin, IIT Kanpur An ICME approach for development of ductile single phase high entropy alloy 9. Tarak Nath Maity, IIT Kanpur Phase separation in mechanically alloyed high entropy alloys 10. Rahul Mane, IIT Hyderabad Powder metallurgy of high entropy alloys 11. GD Sathiaraj, IIT Hyderabad Effect of starting grain size on thermos-mechanical processing response of CoCrFeMnNi high entropy alloy 12. ER Reddy, IIT Hyderabad Microstructure and texture evolution during hot deformation of equiatomic high entropy CoCrFeMnNi alloy 13. G Ramya Sree, University of Hyderabad Understanding structural evolution and associated mechanical behaviour in a Nanocrystalline AlCrCuCoFeNi high entropy alloy system

14. Akanksha Dwivedi, University of Hyderabad Synthesis and mechanical properties of Ti-V-Cr-Zn-Nb multi-component high entropy alloy 15. Abhijit, University of Hyderabad Structural stability of nanocrystalline multi-component Ti-Ni-Cr-Co-Fe alloy 16. Anand Shekar R, IIT Madras Effect of thermo-mechanical processing on the microstructure and mechanical properties of Ti-Al-Ni-Cr-Co based high-entropy alloys 17. Rameshwari Naorem, IIT Kanpur Symmetry considerations for computation of orientational entropy in Jahn-Teller active systems 18. K Guruvidyathri, K.C. Hari Kumar and B.S. Murty, IIT Madras Phase prediction in multicomponent systems through CALPHAD method: A case study on Co-Cr-Fe-Ni System 19. S Ranganathana, S Kashyap1, C Chattopadhyay2, A Takeuchi3, Y Yokoyama3, BS Murty2, 1IISc Bangalore, 2IIT Madras and 3Tohoku University, Japan Amorphisation by destabilisation of binary crystalline intermetallic compound with equiatomic multicomponent substitution 20. Chinmoy Chattopadhyay and BS Murty, IIT Madras Kinetic model for prediction of phase formation in high entropy alloys 21. K Praveen Kumar1 M Gopi Krishna2 J Babu Rao3 NRMR Bhargava3 1R.V.R. & J.C. College of Engineering, Guntur, 2ANU College of Engineering &Technology, Guntur, 3College of Engg., Andhra University, Visakhapatnam Microstructural and mechanical behaviour of 2024 Aluminium - high entropy alloy composites

Oral Presentation Abstracts

Physical Metallurgy of High-Entropy Alloys

Jien-Wei Yeh Department of Materials Science and Engineering National Tsing Hua University, Hongkong

Two definitions of High-Entropy Alloys (HEAs), based on composition and entropy, are reviewed to clarify misunderstandings. Four core effects, i.e. high entropy, sluggish diffusion, severe lattice distortion, and cocktail effects, are mentioned to show the uniqueness of HEAs. Then, current state of Physical Metallurgy is discussed. Physical metallurgy is a branch of materials science, which focuses on the relationship between composition, processing, crystal structure and microstructure, and physical and mechanical properties. The progress of physical metallurgy is over one hundred years and the underlying principles were thought to be mature. However, this was based on the observations on conventional alloys. As phase formation of HEAs is entirely different from that of conventional alloys, physical metallurgy principles may need to be modified for HEAs.

Development of new HEAs was mainly concerned with the trials of different compositions and processing, and the analyses of their properties and microstructure in the first decade after the birth of HEAs in 2004. Now it is time to investigate physical metallurgy of HEAs for an in- deep understanding HEAs, not only satisfying scientists’ curiosity but also helpful in designing and controlling HEAs.

Every aspect of physical metallurgy needs to be re-checked in the world of HEAs and the bridges from conventional alloys to HEAs need to be built in order to get a better understanding of alloys. In this presentation, thermodynamics, kinetics, structure and properties of HEAs are briefly discussed relating with the four core effects of HEAs. Among these, severe lattice distortion effect is particularly emphasized since it exerts direct and indirect influences on many aspects of microstructure and properties. Because a constituent phase in HEAs is ordinarily not based on one major element and its matrix can be regarded as a whole-solute matrix, every lattice site in the matrix has atomic-scale lattice distortion. In such a distorted lattice, point defects, line defects, and planar defects are different from those in conventional matrices in terms of atomic configuration, defect energy, and dynamic behavior. As a result, mechanical properties relating with Young’s modulus, solid solution hardening, serration behavior, work hardening, grain size strengthening, twinning-induced strain hardening, ductility, creep, and fatigue initiation and propagation are influenced by such distortion. In addition, physical properties relating with lattice constant, diffusion, X-ray diffraction, melting temperature, electron mobility, electrical conductivity, thermal conductivity, magnetism, temperature coefficient, and damping capacity also have different trends in HEAs. Most importantly, this presentation points out that lots of future works are required to build suitable mechanisms and theories correlating composition, microstructure and properties for HEAs. Only these understandings would make it possible to complete the physical metallurgy of the alloys world.

Solid Solutions - Their Limits and Extensions

S Ranganathan Department of Materials Engineering Indian Institute of Science, Bangalore 560012

The first alloys encountered by mankind were native alloys like electrum and tumbago. These were followed by the serendipitous discovery of alloys of copper with arsenic in 3000 BCE. These were all solid solutions. It is interesting to note that at the beginning of the third millennium CE studies of high-entropy alloys have brought solid solutions once again to centre study.

The scientific understanding of the formation of solid solutions was first given by Hume- Rothery in his classic 1926 paper. In phase formation he pointed out that size, electronegativity and valence played important roles and identified factors responsible for the formation of solid solutions. In addition, he stated that for forming a continuous series of solid solutions the metals must have the same crystal structure.

David Pettifor in 1984 took the next major step of adding a fourth factor of bond orbitals. He gave each element a Mendellev Number and constructed Pettifor Maps. This has been a powerful device first applied by him to explain the formation of crystalline intermetallics. This was extended to quasicrystals by Jeevan, Ranganathan and Inoue and to glasses by Takeuchi, Inoue, Murty and Ranganathan.

In this presentation, we extend a preliminary study by Biswas and Ranganathan to equiatomic multicomponent high-entropy alloys. It is possible that the cocktail effect is responsible for extending solid solutions beyond that in lower order systems, often overriding the requirement of the same crystal structure. Future lines of investigation will be pointed out.

Accelerated Discovery and Development of Multi-Principle Element Alloys via ICME

D.B. Miracle, O.N. Senkov, J. D. Miller and C. Woodward Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Ohio 45433, USA

Multi-principle element (MPE) alloys (also called high entropy alloys) have 5 or more elements at roughly equivalent concentrations. The vast number of new alloy systems created by this approach gives dramatic new opportunities for discovery and development. However, the immense number of alloy systems also represents the most significant technical barrier. A palette of 40 metal elements offers over 10^10 MPE alloy systems, so that fundamentally new methods are needed to design and evaluate alloy systems rapidly, systematically and effectively. A 3-stage approach is described to rapidly screen and evaluate vast numbers of MPEs for aerospace applications. CALPHAD methods that calculate phase equilibria are integrated with high-throughput experiments on materials libraries with controlled composition and microstructure gradients. Much of this evaluation can be done now, but key components are missing. This ICME methodology will be described, current results will be presented, and required future efforts will be outlined.

Some Observations on Unique Aspects of Mechanical Behaviour of High Entropy Alloys

Rajiv S. Mishra, Nilesh Kumar, Mageshwari Komarasamy Center for Friction Stir Processing, Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203, USA

High entropy alloys are highly concentrated solid solution alloys that exhibit exceptional mechanical properties. In this presentation, the underlying fundamental deformation science will be highlighted. Three distinct areas of focus will be, (a) strain rate dependence, (b) role of nanotwinning, and (c) grain size dependence. A comparison with conventional alloys helps in delineating the micromechanisms. Some thoughts for future research directions will be shared.

Excitement and Challenges in the Field of High Entropy Alloys

B.S. Murty Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras, Chennai- 600 036

High entropy alloys (HEAs) are a new class of multicomponent equiatomic (or near equiatomic) alloys, which form simple solid solutions due to their high configurational entropy. The formation of nanocrystalline HEAs has made them more interesting due to their fundamental and technological importance. The simple structures, high thermal stability of the structures, exceptional mechanical properties, both at ambient and high temperatures, low diffusivities, good corrosion and oxidation resistance are all quite exciting to the scientists in the field.

The challenges in the field include prediction of phases that can form for a given combination of elements and the influence of the processing route on phase formation. A number of thermodynamic and topological parameters are being proposed by many to predict phase formation. The efficacy of these parameters in predicting the phase formation in a variety of HEAs needs to be established. As of now there appears to be no single parameter, which can be universally applied to a wide range of HEAs. It is also important to know the conditions a given HEA forms an amorphous solid solution instead of a crystalline one. It is also challenging to understand whether the phases formed are truly entropy stabilized or kinetically stabilized due to low diffusivities in these multicomponent systems. It is also important to note that all multicomponent equiatomic alloys do not lead to the formation of single phase solid solution or for that matter mixture of solid solutions. In a few cases, they have shown the formation of intermetallic phases and in some cases phase separation of certain elements with high positive enthalpy of mixing with other elements in the alloy. It is important to understand the decomposition behaviour that occurs on a nanoscale in a number of HEAs.

Thermal Spray Routes towards Achieving High Entropy Alloy Phase Structures

Christopher C. Berndt*, Andrew S.M. Ang and Mitchell L. Sesso Swinburne University of Technology, H66, P.O. Box 218, Hawthorn, Victoria 3122, Australia *Adjunct Professor, Dept. of Materials Science and Engineering, Stony Brook University, Stony Brook, NY11794, USA

AmeeyAnupam, S. Praveen, Ravi Sankar Kottada, B.S. Murty Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India

High Entropy Alloys (HEAs) are known for their high temperature microstructural stability, enhanced oxidation and wear resistance properties. HEAs have been deposited as a surface coating in this work by thermal spray methods. Our original aim was to investigate HEAs as an alternative bond coat material for a thermal barrier coating system. Therefore, nanostructured HEAs that were based on AlCoCrFeNi and MnCoCrFeNi were prepared by ball milling and then plasma sprayed. Splat studies were assessed to optimize the appropriate thermal spray parameters and spray deposits were prepared. Subsequently, the microstructure and mechanical properties of two HEAs coatings of different composition were characterized and compared to conventional plasma sprayed NiCrAlY bond coats.

Much has been learned concerning the microstructural and phase stabilities of the so-formed HEA coatings. The presentation in this workshop will focus on our current state-of-the-art knowledge as well as future directions where we seek to fill in the gaps concerning the technology and science.

Challenges in Thermodynamic Modelling of Multicomponent Systems

K.C. Hari Kumar Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras, Chennai- 600 036

Calphad provides a very efficient framework for computing phase stability related information concerning multicomponent materials. Several Gibbs energy databases and computational thermodynamic tools are available for this purpose. Most of the commercial databases are “principal element centric”, therefore not suitable for dealing with phase stability of equiatomic multicomponent alloys, although there is increasing evidence that there is nothing unusual about these alloys from a thermodynamic point of view. In this talk I will outline the challenges in constructing Gibbs energy databases for dealing with multi-principal element alloys.

Orientational High Entropy Alloys

Anandh Subramaniam Materials Science and Engineering Indian Institute of Technology Kanpur, Kanpur-208016

In high entropy alloys (HEA) the configurational entropy, due to the presence of multiple elements, stabilizes a disordered solid solution (DSS) in preference to the possible formation of compounds. In the current work, we identify cluster compounds (of the type AM4X8) as orientational analogues of HEA. In cluster compounds, the role played by ions in the NaCl + – 5+ structure (Na & Cl ) is played by two kinds of clusters in the compound (cubane: (Mo4S4) 5– & tetrahedron: (GaS4) ). In cluster compounds orientational disorder increases the entropy and plays the role analogous to positional disorder in HEA. In the specific example of the GaMo4S8 compound, at temperatures greater than 50K, the entropic benefit more than makes up for the strain energy cost and stabilizes the disordered phase in preference to an orientationally ordered compound (of lower symmetry).

Microstructure and Mechanical, Corrosion and Oxidation Properties of NiTiCuFe Multi-Component Alloy

Anand Sekhar R1, Niraj Nayan2, G Phanikumar1, Bakshi S R1 1Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Madras, Chennai – 600036 2Vikram Sarabhai Space Centre, Thumba, Thiruvananthapuram, Kerala-695022

Alloying can make drastic changes in mechanical and chemical properties. In conventional alloys, addition of other elements is usually restricted to only small amounts. High Entropy Alloys having generally more than five elements in equiatomic compositions show an enormous increase in configurational entropy making it thermally stable even at high temperatures. NiTiCuFe high entropy alloy was prepared using a medium frequency induction melting furnace. Thermodynamic criteria show that this composition can form single phase. Thermo-mechanical processing studies were carried out using Gleeble®3800 to understand the effect of high temperature deformation on the microstructure and mechanical properties of NiTiCuFe HEA. Samples were subjected to deformation at 800, 900 and 1000 °C. Results show good compressive strength up to 1000°C. Room temperature compressive test conducted on the samples shows good compressive strength. The phase evolution after thermo-mechanical processing was studied using XRD. As cast structure showed a mixture of BCC and FCC phase. Thermo-mechanical processing favours the formation of three phases Cu-Ni FCC phase, Fe2Ti Laves phase (C14) and Ni3Ti intermetallic (D024). Microstructural characterization using SEM and TEM confirms the presence of three phases. Effect of phase evolution on the mechanical properties was studied using nano-indentation with a Berkovich indenter. Elastic modulus and hardness of the phases were measured from load the displacement curves. Results explain the contribution of each phase on the mechanical property. Microhardness was also measured on the samples before and after compression. Results shows good hardness values for all the samples. Corrosion behaviour of the alloy was studied using 3.5 wt.% NaCl in distilled water. Results show good corrosion resistance comparable with that of stainless steel.. Oxidation study was also conducted on the samples at 800, 900, 1000 and 1100oC. Results indicate good oxidation resistance up to temperatures of 900oC.

Thermo-Mechanical Processing of FCC CoCrFeMnNi High Entropy Alloy

P.P. Bhattacharjee* Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Hyderabad Ordnance Factory Estate Yeddumailaram 502205

The thermo-mechanical processing behavior of equiatomic FCC CoCrFeMnNi high entropy alloy (HEA) was studied with particular emphasis on the microstructure and texture formation. For this purpose, the alloy was cold-rolled to 90% reduction in thickness and isochronally annealed for one hour at temperatures ranging from 700°C to 1000°C. The deformation texture of the heavily cold-rolled material revealed the presence of a strong brass component ({110}<112>), typical of low stacking fault energy materials. Near ultrafine microstructure was observed after annealing at low temperatures. The annealing texture was characterized by the presence of α-fiber, retained deformation texture components, brass recrystallization component ({236}<385>) and several other different components. However, the volume fraction of different components was not significantly affected by the annealing temperature. The observed microstructural and textural changes were compared and contrasted with other model low SFE alloys to highlight the unique behaviour of the HEA.

HEAs for AUSC plants, Radiation Environment and Gas Turbine Engines

R. Krishnan Ex. BARC & DRDO

High entropy alloys with their significantly enhanced physical and mechanical properties have revolutionised the materials world. Most of these alloys have solidified either in the FCC or the BCC structure, or with one of them as the major phase. It has also been shown that FCC alloys are soft and ductile, while their BCC counterparts are hard but brittle. When one looks for applications in specific areas, one needs to judiciously design the alloy to meet the intended requirements.

This presentation deals with the selection of possible HEAs in three areas, namely advanced ultra-super critical (AUSC) coal powered stations, radiation environment and aero gas turbine engines. With regards to the AUSC boiler tubes, the chosen HEA should have better fireside corrosion and steam side oxidation resistance than the materials already chosen such as Incoloy 740 or Haynes 282. Ductile FCC HEA would meet the requirement, provided it also has the requisite high temperature (> 8500C) mechanical properties. Evaluating the data so far available on HEAs, the suggestions for AUSC applications are: 1. Oxide Dispersion Strengthened low stacking fault energy FCC alloy such as FeCrCoMnNi with Y2O3 dispersions 2. High strength FeCoCrNi2Al alloy with minor additions of Mo, Ti or Si either singly or in combination 3. FCC HEA matrix with B2 dispersions such as AlCoNiFeTi0.4 & AL0.3CoCrFeNi.

As for as radiation environment is concerned, a BCC structure is better as compared to a FCC because the former can accommodate radiation induced point defects more easily. Presently zirconium base alloys are used in thermal reactors, while ferritic steels are used in fast reactors as fuel clads, but these do not have adequate long time radiation resistance to withstand increased fuel burn-up. BCC high entropy alloys with adequate ductility may be a better choice. Component elements in the HEA should decrease the SFE of the alloy such that the material deforms by nano twinning. Nano crystalline structures also assist in this process. The suggestion made with respect to fast breeder reactor fuel clad (may also be suitable for GEN IV reactors) is a combination of FeAlCrMoSiTi, not necessarily in equal atomic proportions, such that one ends up in a low SFE BCC alloy with adequate ductility and strength.

With regards to high pressure gas turbine engine rotors, the main requirement is high temperature capability, with adequate creep resistance. While HEAs possess good mechanical properties, creep resistance is obtained essentially by microstructural control. In this context, multiphase alloys with a disordered (ordered) matrix and ordered (disordered) epitaxial dispersoid may be beneficial. Thus an HEA from NbFeAlCrTiNiMo is worth trying. The microstructure of HEAs like MoNbTaVW should be made multiphase with suitable alloying additions, to make it ductile, while retaining its high temperature strength.

In the ultimate analysis, focus should be on treating HEAs as the base and making minor additions to it to get the desired microstructure and mechanical properties.

High Entropy Alloys: Potential for Airframe Applications

James D Cotton1, Om Prakash2 1Boeing Research & Technology, Seattle, WA, USA 2 Boeing Research & technology India Centre, Bangalore

“High Entropy Alloys” are often characterized as alloys consisting of roughly equal concentrations of at least five metallic elements and are claimed to favor close-packed, disordered structures due to high configurational entropy. Such crystal structures, e.g. face- centered cubic (FCC), hexagonal close-packed (HCP) and body-centered cubic (BCC), are advantageous in that they should offer multiple active slip systems usually observed in ductile metals and alloys. This opens the door to a large number of rich chemistries which would otherwise contain such unacceptably large volume fractions of intermetallic compounds as to not be useful in structural applications.

Despite some thermodynamic arguments for entropic stabilization of simple, disordered phases, the high entropy alloys studied to date typically consist of combinations of elements of known extensive solid solubility. For example, most investigated chemistries are based on a cast CoCrFeNiX type base chemistry, where X = Al, Cu, Mo or Ti. Isolated research in other systems, such as TaNbHfZrTi, has also been conducted. In both systems, FCC and/or BCC crystal structures have been observed to predominate. This raises the question of the effective ability of configurational entropy to extend the useful solid solubility range of the disordered phases. Whether or not entropy plays a significant role in phase selection, the richness of the alloy design space and the breadth of possible microstructures is fascinating, such that the problem becomes more one of deciding on an alloy development direction. This leads to some high-level questions. For example, what is the goal of a high entropy alloy development effort? Can any of the alloys discovered to date compete both economically and technically with those already available, and those in development? What is theoretically achievable in rich, multicomponent compositions? In this paper, Boeing work will be reviewed that has evaluated the potential for low density airframe alloys, as well as a combinatorics-based model for predicting complex alloy behavior in which over 600,000 possible equiatomic compositions containing up to six components were evaluated. Commentary will be offered on potential directions for future work.

High Entropy Alloys to Massive Solid Solution Alloys: Trend in Complex Alloy Design

K. G. Pradeep1,2 1Materials Chemistry, RWTH Aachen University, Kopernikusstr.10, 52074, Aachen, Germany 2Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-str.1, 40237, Düsseldorf, Germany

High entropy alloys (HEA) from its inception has attracted lot of attention due to developing single phase solid solutions from multi-principal constituents. The interest therefore lies in discovering and exploring the physical and mechanical properties arising from multicomponent solid solution strengthening. However, the HEA design as of today is very much empirical and hence only a limited number of single phase solid solution forming systems has been identified. In spite of the fact that the stability of identified single phase solid solutions is still under question, the enormous efforts being employed in this field have provided limited dividends. In order to overcome such deficiencies, the use of nonequiatomic HEA design has been suggested which consistently delivers single phase solid solutions over a wide range of compositions. Even though, the configurational entropy of non-equiatomic HEAs is much lower than their equi-atomic counterparts, the as formed single phase solid solutions are highly stable and exhibit outstanding mechanical properties. Hence, these new class of non- equiatomic multi-component alloys could be termed as massive solid solution alloys owing to their outstanding properties arising out of pure solid solution strengthening. The use of quantum mechanically guided high throughput technology employed for the synthesis of non- equiatomic HEAs will be presented and their outstanding mechanical properties will be discussed.

Analytical Microscopy for Understanding Structure and Chemistry of Multicomponent Alloys

Joysurya Basu Physical Metallurgy Group Indira Gandhi Center for Atomic Research, Kalpakkam-603102, Tamil Nadu, India

Analytical transmission electron microscopy provides an excellent opportunity to study structure and chemistry of multicomponent alloys which is the key to microstructural engineering and optimization of properties. Pertaining to the complex chemistry and variable processing conditions, multicomponent alloys are often held up at local thermodynamic minima. Detailed atomic resolution microscopy not only helps in understanding the phase and the microstructure evolution, but may provide insight into the underlying mechanisms operative along the evolution path. In the present talk, precipitation of carbide phases and their conversion into oxy-carbides at a later stage in Fe-Co-Ni-Cr alloy as studied by STEM-EELS would be discussed. Additionally, crystal nucleation in Zr-Cu-Ni-Al alloy and its relation to polyhedral structures in the liquid phase as studied by quatitative high resolution electron microscopy would be discussed in detail. In course of this presentation, an attempt would be made to explain the fact that analytical electron microscopy not only helps in understanding the phases and microstructures, it does help in understanding the operative underlying mechanisms.

Structure, Phase Stability and Mechanical Properties of Microcrystalline and Nanocrystalline Ti-Ni-Cr-Co-Fe High Entropy Alloy

Abhijit1, P. Sai Karthik2, Ravi C. Gundakaram2, G. Madhusudhan Reddy3 and Koteswararao V. Rajulapati1* 1 School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046, India. 2International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005 3Defence Metallurgical Research Laboratory, Hyderabad 500058

High Entropy Alloys (HEA) are alloys having at least five principal elements and all the principal elements are mixed in equiatomic ratios. HEAs usually form simple solid solutions with fcc and/or bcc structures with no intermetallic compounds and hence have emerged as a new type of advanced metallic materials. HEAs possess some excellent mechanical properties and have great potential to be used as high temperature materials, coating materials requiring high hardness and high wear resistance and corrosion resistance materials with high strength. A multi-component TiNiCrCoFe high entropy alloy is synthesized using vacuum arc melting. Structural details are probed using optical microscopy, XRD, SEM and TEM. Mechanical characterization was done using Vickers microindentation and nanoindentation. Subsequently the as-cast HEA is milled for 30 hours to attain nanocrystalline structure. The nanocrystalline TiNiCrCoFe HEA is then sintered using Spark Plasma Sintering (SPS) at 0.5TM and 0.6TM, and characterized using SEM, XRD and TEM, and also tested for various mechanical properties. The results of both micro-crystalline and nano-crystalline Ti-Ni-Cr-Co-Fe HEA are compared and discussed in detail.

High Entropy Alloys: Probing Defects using Positrons

S. Abhaya Materials Science Group Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102

High entropy alloys (HEAs) are multicomponent equiatomic or near equiatomic alloys which form solid solutions with simple crystal structures owing to their high configurational entropy. Yeh et al. pointed out that the configurational entropy of a binary alloy is maximum when the elements are in equiatomic proportions and that the configurational entropy increases with increasing number of elements in a system. Furthermore, the low diffusivity of the atoms in these multicomponent alloys restricts the formation of the number of phases. Because of the unique equiatomic/near equiatomic composition, the HEAs are bestowed with high strength/hardness, high thermal stability and good corrosion and oxidation resistance.

Defects play an important role in deciding the phase, microstructure and mechanical properties of the high entropy alloys. So, with controlled thermomechanical treatment, one can alter the nature of the defects present thereby changing the so called unique properties of the high entropy alloy. Hence defect characterization becomes an important aspect of HEA. Positron annihilation spectroscopy is an excellent non-destructive defect characterization tool.

This talk will give a flavour of how positron annihilation spectroscopy is useful in understanding a) defect recovery and crystallization in arc melted FeCrCoNi alloy using positron lifetime and b) implantation induced defect evolution and defect annealing in 1.5 MeV Ni implanted FeCrCoNi for two different doses using variable low energy positron beam.

Thermal Stability and Mechanical Behaviour of High Entropy Alloys synthesized by Mechanical Alloying and Spark Plasma Sintering

Ravi Sankar Kottada Indian Institute of Technology Madras, Chennai

The alloy designing of High Entropy Alloys (HEAs) is distinctively different from conventional alloys. This new class of alloys usually consists of more than four elements mixed in equi-atomic proportion, but form a few phases with simple FCC or BCC structures. Most of these HEAs possess very high strength, outstanding thermal stability and excellent strength retention at higher temperatures. Thus, the research in the area of HEAs has been progressing at a rapid pace. In the present study, CoCrFeNi high entropy alloy was synthesized by mechanical alloying and subsequently sintered in a spark plasma-sintering (SPS) unit. Phase evolution during mechanical alloying and phase changes after SPS were studied using XRD and SEM. Thermal stability of the microstructure is studied in the temperature range of 700 – 900C for durations of more than 500 h, which shows that these alloys are extremely stable at temperatures greater than 0.5 Tm. Room temperature as well as high temperature mechanical properties were studied under constant strain rate and under constant stress conditions. This alloy exhibits very high compressive strength of ~2 GPa with plastic strain of 20%. Detailed post-deformation microstructural characterization was done using XRD, SEM and TEM.

Synthesis and Characterization of Light Weight High Entropy Alloy

Jaibeer Singh1, Ornov Maulik1, Vinod Kumar1,2, * 1Department of Metallurgical and Materials Engineering, MNIT Jaipur - 302017 2Adjunct Faculty, Materials Research Centre, MNIT Jaipur - 302017

An AlMgFeCuCrNi based high entropy alloy was synthesized by mechanical alloying followed by conventional sintering. Phase analysis at room temperature was investigated using X-Ray diffraction and SEM. It has been found that two solid-solution phases with body-centered cubic (BCC) and face-centered cubic (FCC) crystal structures form in this alloy. Effect of sintering temperatures, such as 800°C, 850°C and 900°C, on phase evolution and hardness was studied in detail.

High entropy alloys: Pertinent Issues on Processing and Stability

Krishanu Biswas Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur - 208016

Recently, the multicomponent HEAs have attracted a great deal of attention from both academic as well as engineering world because of their ability to form FCC/BCC/HCP solid solutions, unique microstructures and appealing properties. However, the HEA phase formation and stability need to be properly investigated and a proper direction is needed to make them useful for potential applications.

The selection of alloying elements and their composition play crucial role in phase selection. Most importantly, formation of a single phase (FCC or BCC or HCP) is the critical issue that needs to be researched upon. In the present investigation, we shall discuss about ICME approach to select elements and their composition so that a single phase can be obtained in cast alloys. The alloys systems obtained by ICME have further been investigated experimentally to check whether the computational approach can effectively be utilized.

In addition, stability of HEA phases is also a critical issue if we can use them in future applications. In this context, we shall highlight microstructural evolution as well as stability of these novel alloys in this presentation. The specimens are prepared using both casting as well as mechanical alloying followed by spark plasma sintering. The microstructural development of the as processed and heated specimens of different alloy systems, CuZnTiFeCr,CuNi TiFeCoCu and AlCuZnCoNi, AlCuCrNiFe will be dealt with. The microstructural evolution will be discussed with detailed thermodynamical and diffusional calculations. The study will show novel sinter aging technique to improve the hardness of these alloys, making and stabilizing nanocrystalline grains of the HEA phases in the microstructure as well as compositional control of the different HEAs required having good stability at high temperatures.

Studies on CNT Reinforced Nanocrystalline AlCrCuFeNiZn High Entropy Alloy Composite

N.T.B.N. Koundinya and K. Sivaprasad Advanced Materials Processing Laboratory, Department of Metallurgical & Materials Engineering, National Institute of Technology, Tiruchirappalli - 620015, Tamil Nadu, India

Elemental powders were milled for 30 h to form a solid solution of AlCrCuFeNiZn high entropy alloy. To evaluate the effect of CNTs as reinforcement phase, CNTs were added in different fractions in the last one hour of milling. The crystallite size reduced significantly during initial stages of milling. The final crystallite size after 30 h of milling is around 15 nm. Powders were hot compacted at 800C for 2 h under a compaction pressure of 500 MPa. Relatively less densification was achieved (90-95%) because of large strain associated with powders. The sintered samples exhibited separation of phases from single phase BCC to one BCC (13%) and two FCC phases (38%-48% each). The hardness of the sintered alloy was ~ 6.3 GPa and with increasing reinforcement the hardness reduced to 5.6GPa. This is attributed to less densification associated with reinforcement. Indentation based fracture toughness was evaluated on these samples. CNT reinforced samples clearly evidenced an enhanced fracture toughness value, which is attributed to bridging of crack faces by CNTs. Hence, it can be summarized that CNTs as reinforcement phase can enhance fracture toughness even in brittle HEA samples.

Challenges in Extending IRF Concept in the Solidification of Multicomponent Alloys

Gandham Phanikumar Indian Institute of Technology Madras, Chennai

An in-depth understanding of the microstructure evolution can provide regimes of microstructure stability for any newly discovered multi-component alloy. This will help in limiting the uncertainties before the alloy is deployed in demanding applications. Predictive capability in determining the microstructure evolution during solidification of alloys is possible using either computer simulation or analytical calculations. Usage of phase-field simulations coupled with thermodynamic and mobility databases are emerging as a popular technique to predict microstructure evolution in technical / multi-component alloys. The analytical approach to the same would involve coupling a morphological stability criterion and the solution of diffusion field to arrive at the interface temperature of a given phase in a given morphology. Interface response functions (IRF) embed the relationship between the interface temperature on the local composition, gradients and relevant thermo-physical parameters. This method of IRFs has been used earlier to successfully determine complete microstructure maps for alloy systems such as Al-Cu and Al-Ni. In this talk, the challenges in extending this concept to the solidification of multi-component alloys will be discussed. This involves different physical properties that are required for the calculations, verification of the validity of underlying assumptions in the theory and a set of controlled experimental studies.

Challenges in the Atomistic Modelling of Multicomponent Alloys

R. Sankarasubramanian Defence Metallurgical Research Laboratory, Kanchanbagh P.O., Hyderabad – 500059

Integrating microstructrual modelling & simulation with experiments has become an essential part of development of new materials. Material microstructure often spans several decades of lengthscale (say, for example, in the case of nickel base superalloys, from a few atoms (~10- 10m) to a few centimeters (~10-2m)). Simulation of such microstructures requires multiscale modelling, of which, atomistic modelling is an important constituent. Density functional theory (DFT) based first-principles calculations, molecular dynamics and Monte Carlo simulations are widely used atomistic modeling techniques. While each of the techniques has its own merit, there are many challenges while addressing engineering alloys. For example, DFT technique is best suited for ordered compounds but has to be used with care while studying disordered alloys. Molecular dynamics and Monte Carlo simulations require accurate description of interatomic interactions, which are generally not available for multicomponent alloys. In this presentation, some of the key challenges in the atomistic modelling of multicomponent alloys are discussed and possible solutions to overcome the challenges are highlighted.

Microstructure Evolution in Multi-Phase, Multi-Component Alloys

Abhik Choudhury Department of Materials Engineering Indian Institute of Science, Bangalore 560012

Microstructures are important building-blocks for new materials because; several physical properties can be related to the patterns at the microscale. An important processing route in the design of microstructures is through solidification, wherein, the self-organization of the different phases and their morphologies can be engineered by altering one or many of the several processing parameters (velocity, thermal gradients, convective currents etc.), as well as the material constituents (alloy compositions, elements etc.). To perform this in a systematic manner however, will require a good understanding of process→structure and parameter→structure correlationships. In this regard, thermodynamically consistent phase- field models describing microstructural evolution as a function of the process and material parameters are useful.

In this talk I will present microstructural evolution, in binary and ternary alloys, encompassing single-phase dendritic as well as multi-phase eutectic structures. In the context of microstructural design of materials, while binary alloys provide a certain range of attainable microstructures, these possibilities increase with the addition of each single element, thereby the sample space for the engineering of different microstructures and therefore the achievable properties from a given set of material constituents, becomes larger. I will utilize phase field modelling as a tool for establishing process→structure and parameter→structure correlationships in binary and ternary alloys, thus highlighting the utility of the phase field method both in the context of ICME, as well as modelling of microstructures in high-entropy alloys.

Thermodynamic Modelling for Predicting Metallic Glass Formation in High Entropy Alloys

K.S.N. Satish Idury1, B.S. Murty2 and Jatin Bhatt1* 1Department of Metallurgical and Materials Engineering, V.N.I.T Nagpur 2Department of Metallurgical and Materials Engineering, IIT Madras

Metallic glasses (MGs) are potential structural and functional materials on account of their disordered configuration of atoms. Since the discovery of glass formation in metallic system in 1960s, a lot of research in this field culminated into discovery of glass forming alloys that contain elements spanning the entire periodic table. However only certain alloy compositions are known to be good glass formers that can be easily processed and find industrial applications. To augment the industrial applicability of MGs, there exists a need to develop MGs that can be processed through conventional casting techniques and form glass phase in bulk form. In order to meet this challenge of novel glassy alloy development, new perspectives of composition design for BMGs need to be explored. Designing MGs through high entropy alloy (HEA) philosophy is a promising pathway that can radically cut down alloy development time and also might result in MGs with excellent glass forming ability. However, given the number of permutations possible for HEAs to be the order of astronomical number proportions by just considering the conventional metallic elements; there exists a need to find an innovative thermodynamic basis for predicting glass formation apriori. In this paper, PHSS parameter which is developed on the basis of Inoue’s criteria for MG formation is used to distinctly categorize solid solution forming HEAs from MG forming alloys. The efficacy of this parameter is demonstrated for various alloy systems to predict novel MG forming compositions in high entropy regime. To conclude, the capability of the PHSS model and the scope for further research in this direction are discussed.

Poster Presentation Abstracts

Microstructural Characterization of Plasma Sprayed High Entropy Alloy Coatings

Ameey Anupam1, S. Praveen1, A.S.M. Ang2, M.L. Sesso, R.S. Kottada1, B.S. Murty1 and C.C. Berndt2,3 1 Indian Institute of Technology Madras, Chennai, India 2 Swinburne University of Technology, Melbourne, Australia 3 Stony Brook University, Stony Brook, USA

Five-component High Entropy Alloy (HEA) AlCoCrFeNi powders were prepared by 10 hours of Mechanical Alloying (MA), and subsequenlty coated on mild steel substrate via Atmospheric Plasma Spraying (APS). XRD of the MA powder showed predominantly BCC phase with minor FCC phases. These phases transformed to major FCC and minor BCC phases together with oxides upon coating. The coating microstructure studied by XRD, SEM, EPMA and TEM shows formation of 4-component NiCoCrFe-HEA, NiCo phases along with alumina, Al-Cr rich oxides, and mixed oxides. Al, Cr and Fe get preferentially oxidized upon exposure to plasma temperatures of >10,000 K forming various oxides, while NiCoCrFe and NiCo are retained inside the particle. This corroborates transformation of Al-stabilized BCC phase in powders to Al-depleted FCC phase in the coating. This work is geared towards exploring the use of HEA coatings as potential substitutes for current bond coats (MCrAlY, M - Ni, Co) in Thermal Barrier Coating (TBC) systems.

Phase Evolution, Densification, and Compressive Properties of High Entropy Alloys

S. Praveen*, B.S. Murty and Ravi Sankar Kottada Indian Institute of Technology Madras, Chennai

High Entropy alloys that are made up of multi-component (more than four) elements mixed in equi-atomic proportions, have shown extraordinary properties such as strength retention and stability of microstructure at high homologous temperatures. In the present study, mechanical alloying and spark plasma sintering was chosen as a processing route to synthesize dense pellets of various compositions comprising of Al, Co, Cr, Cu, Fe, and Ni. Each of these individual elements has their significant influence on phase evolution and densification. For example, Ni containing alloys tend to form a FCC phase whereas Al containing alloys tend to form a BCC phase, immiscible nature of Cu with most of the elements makes Cu to segregate as a Cu rich FCC phase. Similarly, Cr containing alloys get densified better than other alloys. From the phase evolution and densification studies, CoCrFeNi was chosen as a promising candidate for thermal stability studies, compression testing at room temperature and high temperature, and compression creep. The dense CoCrFeNi alloy did exhibit excellent thermal stability even after annealing at 700oC for 600h by retaining its microstructure, grain size, and hardness. XRD, SEM, TEM and 3DAP characterisation techniques have been utilized at different stages starting from mechanical alloying till mechanical property studies to understand the phase evolution, densification behaviour, and compressive properties.

Alloying and Phase Evolution in Refractory CrMoNbTiW High Entropy Alloy

Lavanya.R1, Ravi Sankar Kottada1, B.S. Murty1 and S.V.S. Narayana Murty2 1Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036 2Advanced Metallography Section, Vikram Sarabhai Space Centre, ISRO, Trivandrum, 695022

Ever since the advent of high entropy alloys (HEAs) in 2004, most of the work on these alloys is focused on involving transition metals such as Fe, Co, Ni and other elements in this series. Recently, the same concept of high entropy emerging from equi-atomic compositions has been extended to elements whose melting point is in the range of 1500 – 3000 C. These alloys are termed as refractory high entropy alloys (R-HEA).

In the present study, primary focus is on understanding the phase evolution in CrMoNbTiW R- HEA. Mechanical alloying of the elemental powders of this alloy resulted in formation of a single BCC phase. Mechanically alloyed powders were sintered in commercial spark plasma sintering to obtain dense pellets. XRD, SEM and TEM were extensively utilized to do detailed microstructural characterization of the powders and sintered pellets. Hardness measurements and preliminary compression tests were carried out on the sintered pellets. Phase evolution and preliminary mechanical properties are compared with R-HEAs obtained through casting route.

Design of High Entropy Metallic glass Compositions from Invariant Reactions Predicted by CALPHAD Methods through PHSS Parameter

K.S.N. Satish Idury1, B.S. Murty2 and Jatin Bhatt1* 1Department of Metallurgical and Materials Engineering, V.N.I.T Nagpur 2Department of Metallurgical and Materials Engineering, IIT Madras

High Entropy alloys (HEAs) currently garner huge interest in materials research domain in view of their exceptional properties [1]. The greatest advantage that can be derived from designing metallic alloys through this perspective is the simplification of alloy design in addition to realization of four core effects (high entropy effect, sluggish diffusion, lattice distortion and cocktail effect) inherent to alloys with equi/near equi atomic concentrations [2]. Simplification of alloy design can be of great boon to metallic glass (MG) research community to explore glass formation in highly untapped regions in compositional space of multi component alloys. Currently, capturing the window of mixing enthalpy (∆Hmix) and topological strain (δ parameter, ΔSσ /kB) of alloys in high entropy regime is the popular method to distinguish between MG forming and solid solution forming HEAs [3, 4].

However, while predicting MG formation through the optimized window of thermodynamic and topological parameters, caution need to be exercised. This work emphasizes that careful consideration of glass formation in the sub binary, ternary and quaternary systems of a multi component alloy can provide a reliable guideline to design high entropy MG formers. This fact is demonstrated by substituting Be Hf and Al to quaternary eutectic regions of Zr-Ti-Cu-Ni alloys and evaluating their propensity for glass formation at equi atomic concentrations. By analyzing their thermodynamic driving force through novel PHSS parameter [5] which is designed based on Inoue’s criteria for glass formation, these alloy systems are ranked based on PHSS parametric ranges. Zr-Ti-Cu-Ni-Be system is demonstrated to be the alloy system with excellent glass forming ability (GFA) in comparison to Zr-Ti-Cu-Ni-Al and Zr-Ti-Cu-Ni-Hf. The origin of excellent GFA for Zr-Ti-Cu-Ni-Be system is attributed to ternary equi atomic Zr- Ti-Be [6] alloy which enables glass formation in multitude of higher order alloy systems. It is opined that though many deep eutectic regions exist in higher order alloy systems, only certain compositional regions among these deep eutectics have superior GFA and enable optimum glass formation in high entropy regimes. This work proves that phase stability data of ternary phase diagrams is of immense help to predict GFA in high entropy alloys. To conclude, this work also advocates that more work need to be undertaken to assess whether invariant reactions predicted for multi component alloys through CALPHAD methods can provide positive direction to the development of high entropy metallic glasses.

References: 1. B.S. Murty, J.W. Yeh, S. Ranganathan, High Entropy Alloys, BH, 2014 2. Y. Zhang, T.T. Zuo, Zhi Tang, M.C. Gao, K.A. Dahmen, P.K. Liaw, Z.P. Lu, Progress in Materials Science, 61 (2014), pp.1-93 3. S. Guo, Q.Hu, Chun Ng, C.T. Liu, Intermetallics 41 (2013), pp.96-103 4. A. Takeuchi, K. Amiya, T. Wada, K. Yubuta, W. Zhang, A. Makino, Mater. Trans. 55 (2014) pp. 165-170 5. B.R. Rao, M.Srinivas, A.K. Shah, A.S. Gandhi, B.S. Murty, Intermetallics, 35 (2013), pp. 73-81 6. A. Wiest, G. Duan, M.D. Demetriou, L.A. Wiest, A. Peck, G. Kaltenboeck, B. Wiest, W.L. Johnson, Acta Mater 56 (2008), pp.2625-2630

Carbide Formation during Synthesis of Co-Cu-Fe-Mn-Ni -W Multicomponent Alloys by Mechanical Alloying and Spark plasma Sintering Route

Anoop K., Pramod S.L. and Srinivasa R, Bakshi Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036

High entropy alloys (HEA) having four or more elements in equi-atomic proportions and having simple crystal structures are attracting researchers due to their promising properties like high temperature stability and good mechanical properties. In the present study, the alloys FeCoMnW, FeCoMnCuW, FeCoMnNiW and FeCoMnNiCuW were synthesized by high energy ball milling of elemental powders followed by Spark Plasma Sintering (SPS). The compositions were selected to produce promising tool materials. XRD analysis of the 20 hr milled powders indicated formation of two phases (1BCC and 1FCC) and WC contamination in the powders. SEM EDS showed excellent homogeneity of the composition in the powders. XRD analysis of the sintered samples showed presence of WC and (Fe,Mn)3W3C and peaks corresponding to the matrix. SEM analysis showed presence of blocky carbide particles in multi-component matrix. CHN analysis of milled powder showed about 2 wt.% carbon in the milled powders which was formed due to dissociation of Toluene. The carbon was found to be sufficient to generate high amount of carbides in the sintered samples. The carbide morphology changed with composition. Hardness of samples was studies.

Synthesis and Characterization of FeAlZnCrCuMgSi and FeAlZnCrCuMgMn High Entropy Alloys by Mechanical Alloying

Nandini Singh* and N.K. Mukhopadhyay Department of Metallurgical Engineering, IIT BHU, Varanasi-221005

Traditional trend has been to design alloy by taking one base metal with minor addition of other constituent elements. Incorporation of more multiprincipal elements often leads to the formation of intermetallics or other complex structures which are brittle and difficult to process. However this paradigm of design has been proved to be false with the advent of High entropy alloys(HEAs). HEAs being defined as Multi-component alloys containing atleast five principal elements with concentration between 5at% and 35at% are potential applicants for high temperature structural materials and bear improved hardness, oxidation resistance and corrosion resistance. In present work FeAlZnCrCuMgSi and FeAlZnCrCuMgMn HEAs were synthesized by Mechanical alloying for 50hrs using PM400(Restch®). Purpose of present work was to study the effect of addition of metalloid Si with DC structure and Mn metal with almost same size and electronegativity to earlier synthesized FeAlZnCrCuMg HEA. Phase was determined by XRD and TEM. Both the alloys consist of single solid solution BCC phase. Crystallite size and lattice strain as determined after 50 hrs of milling for FeAlZnCrCuMgSi alloy were 38nm and 0.66% respectively. For same duration of milling for FeAlZnCrCuMgMn alloy, crystallite size and lattice strain were 51nm and 0.71% respectively. SEM was used for compositional analysis and powder size determination at different times of milling. Hardness of sintered powder alloys FeAlZnCrCuMgSi and FeAlZnCrCuMgMn obtained after 50hrs milling came out to be 623HV and 426HV respectively. Efforts will be made to understand the structural evolution, stability and the mechanical properties of the milled HEAs.

Synthesis and Characterization of Fe-Al-Zn-Cr-Cu-Mg and Fe-Al-Zn-Cr- Cu-Mg-Co High Entropy Alloys by High Energy Ball Milling

Vikas Shivam*, Santhosh K. Alla, R.K Mandal and N.K. Mukhopadhyay Department of Metallurgical Engineering, Indian Institute of Technology (BHU), Varanasi-221005

The design of conventional multicomponent alloy systems includes one major element along with the additions other elements and seldom has it required more than three principal metallic elements. Generally, this type of multicomponent alloys always display formation of solid solution along with intermetallic compounds and complex microstructural forms. But, high entropy alloys (HEAs) are the multicomponent alloys having at least five principal metallic elements without the formation of intermetallic compounds. These HEAs possess excellent properties like higher hardness, strength as well as improved wear, oxidation, good corrosion resistance and other functional properties. The purpose of present work is to design and develop new high entropy alloy avoiding HCP structure. With this consideration, Fe-Al-Zn- Cr-Cu-Mg and Fe-Al-Zn-Cr-Cu-Mg-Co high entropy alloys were selected for mechanical alloying. Alloys were synthesized by high energy ball milling using P-5 Planetary ball mill PM400 (Retch) up to 45 hours. Structural characterization has been carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In both the cases, body-centered cubic (bcc) structure with lattice parameter of 2.88 Å was observed. Microhardness of FeAlZnCrCuMg high entropy alloy sintered at 900 °C was 910 HV. All FeAl, FeAlZn, FeAlZnCr, FeAlZnCrCu, FeAlZnCrCuMg five systems are forming BCC structure and FeAlZnCrCuMgCo also forming nearly single phase BCC structure. It should be noted that, all systems are having BCC structure elements like Fe and Cr are stronger elements which are more open structure with high melting point. This may be the reason that formation of BCC structure in these systems. Finally, even though, constituents of two alloys are having different crystal structure and large difference in the atomic radii, showing formation of single phase. Attempts will be made to discuss the results on the structure and stability of the phases during milling.

An ICME approach for Development of Ductile Single Phase High Entropy Alloy

Tazuddin, N. P. Gurao, Krishanu Biswas* Department of Materials Science and Engineering, Indian Institute of Technology Kanpur Kanpur-208016

High Entropy Alloy (HEA) is a new class of material with tunable properties that have excellent potential to be used in high temperature, aerospace, automotive and biomedical applications. The HEAs derive their exceptional properties like excellent strength, oxidation resistance, wear and corrosion resistance due to their higher configurational entropy (≥1.61R) compared to conventional multi element alloys. These properties along with ductility are expected to be enhanced in single phase high entropy alloys. However, till date only few single phase HEAs with five or more elements have been found and only one study on secondary processing of these alloys by cold rolling has been reported. Integrated computational materials engineering (ICME) approach is very effective in terms of cost and time to develop and optimize new alloys. In the present investigation, we apply CALPHAD (CALculation of PHAse Diagrams) approach to unearth a single phase FCC HEA composition of equiatomic MnCuCoFeNi HEA. The cast alloy after homogenization could be subjected to cold rolling to 90% thickness reduction and showed a single component Brass {110}<1-12> texture which is characteristic of low stacking fault energy FCC material. There was an increase in hardness with rolling and the hardness more than doubled after 90% rolling reduction (163±8.5 to 399±5.96 VHN) like conventional FCC materials deforming by dislocation activity. The formation of characteristic Brass component can be attributed to extensive planar slip in the low SFE HEA. The deformation texture remained unaltered with decrease in hardness (399±5.96 to 191±2.61 VHN) after annealing to temperature as high as 900 °C (0.75 Tm) for one hour. It is expected that ductile MnCuCoFeNi HEA can have excellent creep and oxidation resistance and can be used for engineering applications at high temperature.

Phase Separation in Mechanically Alloyed High Entropy Alloys (HEAs)

Taraknath Maity, Sutanuka Mohanty and Krishanu Biswas Department of Materials Science and Engineering, Indian Institute of Technology Kanpur 208016

The multi-component high entropy alloys (HEAs) are defined as solid solution alloys containing equal to or more than five principal elements in equal or near equal atomic percentage [1]. In the earlier investigation, it has been explored that multi principal elements in alloys leads to the formation of intermetallic phases, complex microstructure and poor mechanical properties. However, the HEAs are found to be consisting of FCC and/or BCC phases and HCP phase [2]. Therefore these alloys are drawing the attention in both scientific and technological community as they exhibit interesting fundamental physics and technological promises [2]. In the literature, most of the HEAs are reported to be multiphase rather than single-phase solid solutions. Phase separations have been observed in HEAs e.g. in AlCoNiCuZn [2], AlCoCrFeNi [3]. The microstructure of as cast AlCoCrFeNi HEAs shows clearly distinguishable dendrites and interdendrites that has been investigated using transmission electron microscopy and atom probe tomography indicating the formation of Cr-Fe rich precipitate into Al-Ni rich matrix. AlCoNiCuZn HEA revealed the formation of ordered LI2 structure within the grains of FCC HEA [2].

The present investigation is, therefore, focused on the phase separation in equiatomic multi component TiFeNiCoCu and AlCoCrFeNi HEAs, prepared by mechanical alloying under protective argon atmosphere followed by consolidation using spark plasma sintering (SPS) at different sintering temperatures. Both the as milled powder and sintered specimens are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) for phase identification. The detailed XRD of TiFeNiCoCu HEA (fig.1a) indicate the presence of a single phase , FCC (α) solid solution in 15 hours ball milled powder and after consolidation of the powder using SPS at different temperatures indicate the presence of one major FCC1 (β) phase and another minor FCC2 (γ) phase. SEM micrograph of sintered sample shows spinodally decomposed microstructure consisting of FCC (Cu)SS and FCC (Co)SS phases. The detailed XRD of AlCoCrFeNi HEA (fig.1b) indicates the presence of a single phase, FCC (γ) solid solution in the 25 hours ball milled powder. However the sintering of the as-milled powder at 900 ºC and 1000 ºC revealed the formation of σ (Fe-Cr) phase in an Al-Ni rich matrix with ordered FCC (LI2) structure. The hardness studies show significant increase from 1.54 to 8.1 GPa as the sintering temperature increases from 800 ºC to 1000 ºC because of the formation of σ (Fe-Cr) phase.

Fig.1a X-ray diffraction patterns of TiFeCoNiCu HEAs pellets sintered at different sintering temperatures. The pattern at the bottom is from 15 hours ball milled sample.

Fig.1b X-ray diffraction patterns of AlCoCrFeNi HEAs pellets sintered at different sintering temperatures. The pattern at the bottom is from 25 hours ball milled powder

References:

1. Yong Zhang, Ting Ting Zuo, Zhi Tang, Michael C. Gao, Karin A. Dahmen, Peter K. Liaw, Zhao Ping Lu, Prog. Mater. Sci. 61 (2014) 1–93 2. Sutanuka Mohanty, N.P Gurao, Krishanu Biswas, Mater. Sci. Eng..A, 617 (2014) 211-218 3. A. Manzoni, H. Daoud, R. Volkl, U. Glatzel, N. Wanderka, Ultramicroscopy 132 (2013) 212–215.

Powder Metallurgy of High Entropy Alloys

Rahul Mane, Ashif Equbal, Y. Rajkumar, Bharat B. Panigrahi* Department of Materials Science and Metallurgical Engineering Indian Institute of Technology Hyderabad, Yeddumailaram, 502205

High entropy alloys are relatively new class of alloy, having minimum five principal components with high configurational entropy. The mixing of the elements are done usually in equiatomic ratio. However, some non-equiatomic elements in small fractions may be added to alter the properties of the alloy. These alloys exhibit unique combination of properties such as, high strength combined with relatively high ductility, high oxidation and corrosion resistance, etc. This material has potential to replace many of the existing super-alloys and high temperature materials in various engineering and strategic applications. Induction melting or arc-melting and castings have been the conventional route to produce bulk material. Since manufacturing through powder metallurgy (PM) has several advantages for many applications; it is the need of the hour to investigate the potential of these alloys for PM processing route. So far, the mechanical alloying of elemental powders has been there for producing high entropy alloy powders. However, there have been many issues in mechanical alloying route and subsequent sintering stages; which need to be understood. Some of the objectives of the present study are: synthesis and optimization of alloying conditions, study the sintering bahviour and their phase evolution during sintering. Initially the work was started with the preparation of FeCrCoMnNi alloy and has been extended to the other alloys systems. A planetary ball mill with tungsten carbide milling system has been used in this study to synthesise the powder. Sintering studies have been carried out in under inert atmosphere and vacuum.

Effect of Starting Grain size on Thermos-Mechanical Processing Response of CoCrFeMnNi High Entropy Alloy

G.D. Sathiaraj, P.P. Bhattacharjee* Department of Materials Science and Metallurgical Engineering Indian Institute of Technology Hyderabad Ordnance Factory Estate, Yeddumailaram, 502205

The effect of initial grain size on the formation of microstructure and texture in heavily cold rolled equiatomic CoCrFeMnNi high entropy alloy (HEA) was investigated. For this purpose two alloys with average grain size ̴7 µm (fine grained starting material or FGSM) and 200 µm (coarse grained starting material or CGSM) were cold-rolled to 95% reduction in thickness and isochronally annealed for one hour over a wide temperature range. The FGSM showed finer grain size as compared to CGSM after annealing at high temperatures. In contrast, the starting grain sizes did not show any pronounced effect on texture formation. The mechanism of texture evolution could be explained based on the absence of preferential nucleation and growth in the experimental HEA.

Microstructure and Texture Evolution during Hot Deformation of Equiatomic High Entropy CoCrFeMnNi Alloy

E.R. Reddy, P.P. Bhattacharjee* Department of Materials and Metallurgical Engineering Indian Institute of Technology Hyderabad ODF Estate, Yeddumailaram 502205

High Entropy Alloys (HEAs) are multicomponent equiatomic or near equiatomic alloys which exhibit many novel properties. The present work attempts to investigate the evolution of microstructure and texture during hot deformation of CoCrFeMnNi alloy. Hot deformation of this material is carried out to 60% reduction by uniaxial compression over a wide range of temperature (700°C-1000°C) and strain rate (0.001/s-1/s). The evolution of microstructure and texture are investigated using Electron Backscatter Diffraction (EBSD). The present results show that hot deformation can lead to the formation of near ultrafine microstructure and characteristic texture in HEAs.

Understanding Structural Evolution and Associated Mechanical Behaviour in a Nanocrystalline AlCrCuCoFeNi High Entropy Alloy System

G. Ramya Sree1, Ravi C. Gundakaram2 and Koteswararao V. Rajulapati1* 1School of Engineering Sciences and Technology University of Hyderabad, Hyderabad 500046 2International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005.

Nanocrystalline AlCrCuCoFeNi High Entropy Alloy (HEA) was synthesized by mechanical alloying of Al, Cu, Cr, Co, Fe and Ni elemental powders in equal atomic ratios for 60 hours where the ball to powder weight ratio was 5:1. Alloy after milling period showed a plate like structure with thickness of about 1 µm. Structural characterization was done using XRD, SEM and TEM. The crystallite size gradually decreased and reached a saturated size of 9 nm with milling time (measured using TEM analysis). As the milling time increased all the elemental peaks disappeared and formed a single solid solution with FCC crystal structure. Spark Plasma Sintering (SPS) is being used to make bulk components out of the milled powders. Mechanical behavior has been investigated using microindentation and nanoindentation. In the end structure-property correlations will be discussed and challenges will be outlined.

Synthesis and Mechanical Properties of Ti-V-Cr-Zn-Nb Multi-Component High Entropy Alloy

Akanksha Dwivedi1, Ravi C. Gundakaram2 and Koteswararao V. Rajulapati1,* 1School of Engineering Sciences and Technology University of Hyderabad, Hyderabad-500046 2International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005

Traditional alloys are based on one or two major principal elements. High entropy alloys are equiatomic multicomponent alloys, wherein configurational entropy increases and hence single phase solid solution is obtained. These alloys can be potentially used in different application that demand high temperature strength, oxidation resistance, corrosion resistance and wear resistance. The present study describes the synthesis and characterization of a novel nanocrystalline equiatomic Ti-V-Cr-Zn-Nb high entropy alloy by mechanical alloying and spark plasma sintering. The prepared high entropy alloy was characterized for its structural, morphological, compositional and thermal properties by using XRD, SEM, EDS, DSC and TEM. The effects of milling duration on phase and structure evolution were investigated. Average crystallite size was measured by TEM. The 60 hours ball milled powder was found to exhibit the lattice parameter and average crystallite size as 4.203A° and 7.0 nm respectively. The prepared alloy was observed to be solid solution having FCC crystal structure by XRD. The obtained powders are consolidated into bulk components using spark plasma sintering and the mechanical properties are being evaluated using Vickers microindentation and depth sensing nanoindentation. In the end structure-property correlations will be established in this novel alloy system.

Structural Stability of Nanocrystalline Multi-Component Ti-Ni-Cr-Co-Fe Alloy

Abhijit1, Muvva D. Prasad2 and Koteswararao V. Rajulapati1* 1 School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046 2Centre for Nanotechnology, University of Hyderabad, Hyderabad 500046

In the present work, a new HEA system was synthesized, characterized and analyzed. Ti-Ni- Cr-Co-Fe alloy was prepared from the powders of individual elements in equiatomic ratio through vacuum arc melting route. As-cast alloy possessed heterogeneous microstructural details. In order to break this heterogeneity, the sample was subjected to ball milling. Mechanical alloying of this cast sample was carried out using SPEX 8000D high energy ball mill and it resulted in homogeneous single solid solution. The milled powder samples were sintered using spark plasma sintering at 0.5TM and 0.6TM (where TM is the theoretical melting point of this alloy, 1885.6 K). These sintered samples were then characterized using XRD, SEM-EDS for compositional analysis and TEM. In this poster, the final structural details will be presented and stability issues/challenges will be outlined.

Effect of Thermo-Mechanical Processing on the Microstructure and Mechanical Properties of Ti-Al-Ni-Cr-Co based High-Entropy Alloys

Anand Sekhar R1, Niraj Nayan2, G Phanikumar1, Bakshi S R1, 1Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Madras, Chennai – 600036 2Vikram Sarabhai Space Centre, Thumba, Thiruvananthapuram - 695022

The objective of this work was to synthesize TiAlNiCr and TiAlNiCrCo multicomponent alloys and study their microstructure and mechanical properties. The alloy powders were prepared by ball milling of elemental powders and consolidated by Spark Plasma Sintering (SPS). These alloy compositions show two BCC phases after 8 hours of milling. Thermo- mechanical processing studies were carried out using Gleeble®3800 to understand the effect of high temperature deformation on the microstructure and mechanical properties of these HEAs. Samples were subjected to compression tests at 600, 700, 800, 900 and 1000 °C. Room temperature compressive test were also conducted on the samples. The phase evolution after the compression tests were studied using XRD. Microstructural characterization was done using Optical microscope and SEM. Effect of phase evolution on the mechanical properties was studied using nano-indentation with a Berkovich indenter. Elastic modulus and hardness of the phases were measured from load the displacement curves. Results explain the contribution of each phase on the mechanical property. Microhardness was also measured on the samples before and after compression.

Symmetry Considerations for Computation of Orientational Entropy in Jahn-Teller active systems

Rameshwari Naorem, Anandh Subramaniam Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur-208016

In Orientational High Entropy Alloys (OHEA) the entropic benefit more than makes up for the strain energy cost and stabilizes the disordered phase in preference to an orientationally ordered compound (of lower symmetry). In one class of OHEA reported, the degeneracy of multiple orientations of the distorted polyhedron gives rise to the entropy in the disordered state, which arises due to Jahn-Teller effect. For crystal structures with ocathedrally and tetrahedrally coordinated metal ions (d-orbital bonding), which display Jahn-Teller distortion, the number of orientational variants can be computed using crystallographic equivalence. In the current work the configurational entropy benefit due to the orientational degeneracy is calculated for systems, wherein Jahn-Teller distortion (due to removal of eg degeneracy for octahedral coordination and t2 degeneracy for tetrahedral coordination) leads to a lowering of the symmetry of the coordination polyhedron. A subset of these Jahn-Teller active crystals are orientational high entropy systems.

Keywords: Orientational High Entropy Alloys, Orientational Disorder, Jahn-Teller Distortion.

Phase Prediction in Multi-principal Element Systems through CALPHAD Method: A case study on Co-Cr-Fe-Ni System

K. Guruvidyathri, B.S. Murty and K.C. Hari Kumar Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras, Chennai 600036

The name high entropy alloys was first used about a decade ago [1] for equiatomic/near equiatomic multicomponent alloys. The high configurational entropy resulting from such compositions was believed to stabilize simple solid solutions in their microstructure [2,3]. Quantities such as Gibbs energy, enthalpy of mixing, atomic size mismatch, valence electron concentration, electronegativity difference, etc. are also have been used explain their formation [4,5]. Moreover, kinetic factors are also expected to play a role in deciding the long-time stability of these phases at elevated phases.

In order to develop better understanding on phase formation in such alloys, phase prediction by computational materials thermodynamics has been attempted in this study. CALPHAD (CALculaion of PHAse Diagram) technique for phase prediction has proven to be successful in the last few decades [6]. The challenge in applying this technique for equiatomic/ near equiatomic multicomponent alloys is in developing a database that works for wider range of compositions [7].

For Co-Cr-Fe-Ni system such a database is made and the vertical sections of phase diagrams are computed. Experimentally, a single phase FCC solid solution is observed in this system for equiatomic composition at room temperature [8,9]. Interestingly, the predicted vertical sections show that single phase FCC is possible only at high temperature range. About 600°C and below more than one phase is seen. Long term heat treatments for about 15 days at 600°C have been carried out to see whether it results in more than one phase as predicted by CALPHAD. This is expected to bring insight into the reason behind the stability of single phase FCC in this system.

References:

1. J.W. Yeh, S.K. Chen, J.Y. Gan, T.S. Chin, T.T. Shun, C.H. Tsau and S.Y. Chang, Adv. Eng. Mater., 6 (2004) 299–303. 2. S. Praveen, B.S. Murty and Ravi S. Kottada, Mater. Sci. Eng. A, 534 (2012) 83– 89. 3. F. Otto, Y. Yang, H. Bei and E.P. George Acta Mater., 61 (2013) 2628–2638. 4. Y. Zhang, Y. J. Zhou, J. P. Lin, G. L. Chen and P. K. Liaw, Adv. Eng. Mater., 10 (2008), 534- 538. 5. A. K. Singh and A. Subramaniam, J. Alloys Compd., 587 (2014), 113-119. 6. N. Saunders and A. P. Miodownik, CALPHAD (Calculation of Phase Diagrams): A Comprehensive Guide, Pergamon (1998). 7. F. Zhang, C. Zhang, S. L. Chen, J. Zhu, W. S. Cao and U. R. Kattner, CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry, 45 (2014), 1–10. 8. S. Guo, C. Ng, Z. Wang and C. T. Liu, J. Alloys Compd., 583 (2014), 410-413. 9. A. Durga, K.C. Hari Kumar and B.S. Murty, Trans Ind. Inst. Metals, 65 (2012) 375-380.

Amorphisation by destabilisation of binary crystalline intermetallic compound with equiatomic multicomponent substitution

S. Ranganathana, S. Kashyapa, C. Chattopadhyayb, A. Takeuchic, Y. Yokoyamac, B.S. Murtyb aDepartment of Materials Engineering, Indian Institute of Science, Bangalore - 560012 bDepartment of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai - 600036 cInstitute of Materials Research, Tohoku University, Sendai, Japan

The present work investigates the effects of equiatomic substitution of two or more elements in place of each element in stable binary intermetallic compounds. Thus, highly stable, binary intermetallic compounds Ni2Ti (alloy 1), NiTi (alloy 2) and NiTi2 (alloy 3) were chosen and Ni and Ti were substituted with Ni-Cu and Ti-Zr-Hf, respectively, in equiatomic proportions. Electric arc furnace melting and thereafter melt spinning were utilised to form amorphous alloys. The XRD, DSC and TEM studies revealed that the alloys formed complete amorphous structure. Very interestingly, the crystallisation studies of the three alloys show that alloy 1 and 2 show considerably high temperature of crystallisation (above 750 K) and high activation energy of crystallisation (435 and 452 kJ/mol for alloy 1 and 386 and 347 kJ/mol for alloy 2), which invariably indicate that the amorphous structure is highly stable in these alloys.

Kinetic Model for Prediction of Phase Formation in High Entropy Alloys

C. Chattopadhyay and B.S. Murty* Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras, Chennai -600036, India.

A completely predictive theoretical model has been proposed which is principally based on kinetic parameter, viscosity, along with several thermodynamic and structural properties of the final alloy based on the constituting elements. In order to predict the phase formation among amorphous, BCC, FCC or HCP phases, TTT diagrams of four experimentally examined alloys, ZrTiCuNiBe, AlCoCrFeNi, CoCrFeMnNi and AlCuMgMnZn, were generated with the help of the viscosity data. The prediction of amorphous, BCC and FCC phase in these alloys matches excellently with the experimental findings. The present approach acts as an efficient guide for the cooling rate that should be adopted for obtaining a particular phase in a given multicomponent equiatomic elemental combination, via the critical cooling rate Rc obtained through the predicted TTT diagrams.

Microstructural and mechanical behaviour of 2024 aluminium - high entropy alloy composites

K Praveen Kumar1 M Gopi Krishna2 J Babu Rao3 NRMR Bhargava3 1Dept. of Mechanical Engineering, R.V.R. & J.C. College of Engineering, Guntur-522019 2Dept. of Mechanical Engineering, ANU College of Engineering &Technology, Guntur- 522510 3Dept. of Metallurgical Engineering, College of Engg., Andhra University, Visakhapatnam- 530003

Work has been carried out to produce composites with high strength and good ductility by maximizing a uniform and smooth interface for effective transfer of load and minimizing reinforcement agglomerations / cracking / pull outs. High strength, high entropy alloy (ternary) in particulate (HEAp) form was used as reinforcement in 2024 aluminium. AA 2024-HEAp composite was prepared through stir cast route by dispersing an average particle size of 125 μm as reinforcement with various weight fractions varying between 5 and 15%. Subsequently, billets were hot extruded to 14 mm Ø rods. All the extrudates were thoroughly homogenized with industrial furnace at 1000C for 24 hours. The mechanical behaviour of alloy and composites was studied in terms of resistivity, hardness, and tensile studies. An increment of 62% in hardness has been observed. Increased reinforcement contents enhance the mechanical properties such as yield strength, tensile strength and Young’s modulus.

Keywords: Metal Matrix Composites, Stir-casting, Composite Metallic Materials, High Entropy alloy.

List of Participants for the Workshop

S.No Name Institute E-mail ID 1. JW Yeh National Tsing Hua [email protected] University, Taiwan 2. D Miracle US Air Force Base, USA [email protected] 3. Rajiv Mishra University of North [email protected] Texas, USA 4. Chris Berndt Swinburne University, [email protected] Australia 5. James D Cotton Boeing Research & [email protected] Technology, USA 6. John Lembo Boeing Research & [email protected] Technology, USA 7. Natalia Boeing research & Natalia.m.mitropolskaya@boein Mitropolskaya Technology, Russia g.com 8. Mahender Reddy Boeing Research & [email protected] Technology, USA 9. Sera Wang Boeing Research & [email protected] Technology, USA 10. KG Pradeep RWTH Aachen, [email protected] Germany 11. R Krishnan Bangalore [email protected] 12. Umesh Waghmare JNCASR, Bangalore [email protected] 13. Meha Bhogra JNCASR, Bangalore [email protected] 14. S Ranganathan IISc Bangalore [email protected] 15. K Chattopadhyay IISc Bangalore [email protected].ernet.in 16. AH Chokshi IISc Bangalore [email protected] 17. Abhik Chowdhury IISc Bangalore [email protected] 18. Vijay Sethuraman IISc Bangalore [email protected] 19. Sanjay Kasyap IISc Bangalore [email protected] 20. M Surendra Kumar IISc Bangalore [email protected] 21. Shalini Roy IISc Bangalore [email protected] 22. Praful Pandey IISc Bangalore [email protected] 23. VS Raja IIT Bombay [email protected] 24. Prita Pant IIT Bombay [email protected] 25. Gururajan IIT Bombay [email protected] 26. Pinaki Bhattacharjee IIT Hyderabad [email protected] 27. BB Panigrahi IIT Hyderabad [email protected] 28. Saswata IIT Hyderabad [email protected] Bhattacharya 29. Rahul Mane IIT Hyderabad [email protected] 30. GD Sathiaraj IIT Hyderabad [email protected] 31. E Rajeshwar Reddy IIT Hyderabad [email protected] 32. Y Rajkumar IIT Hyderabad [email protected] 33. K Biswas IIT Kanpur [email protected] 34. Anand Subramanian IIT Kanpur [email protected] 35. Nilesh Gurao IIT Kanpur [email protected]

36. Kaustubh Kulkarni IIT Kanpur [email protected] 37. K Mondal IIT Kanpur [email protected] 38. Tazuddin IIT Kanpur [email protected] 39. Tarak Nath Maity IIT Kanpur [email protected] 40. Rameshwari IIT Kanpur [email protected] Naorem 41. Surekha Yadav IIT Kanpur [email protected] 42. Rahul Mitra IIT Kharagpur [email protected] 43. BS Murty IIT Madras [email protected] 44. KC Harikumar IIT Madras [email protected] 45. Srinivas Rao Bakshi IIT Madras [email protected] 46. Ravi Sankar Kottada IIT Madras [email protected] 47. G Phanikumar IIT Madras [email protected] 48. VS Sarma IIT Madras [email protected] 49. Anand Kanjarla IIT Madras [email protected] 50. Uday Chakkingal IIT Madras [email protected] 51. V Srinivas IIT Madras [email protected] 52. S Varalakshmi IIT Madras [email protected] 53. Chinmoy IIT Madras [email protected] Chattopadhyay 54. S Praveen IIT Madras [email protected] 55. K Guruvidyathri IIT Madras [email protected] 56. Ameey Anupam IIT Madras [email protected] 57. R Lavanya IIT Madras [email protected] 58. Anoop K IIT Madras [email protected] 59. Anand Shekar R IIT Madras [email protected] 60. Adil Shaik IIT Madras [email protected] 61. Raghavendra IIT Madras [email protected] Kulkarni 62. R Anil Prasad IIT Madras [email protected] 63. NK Mukhopadhyay IIT BHU, Varanasi [email protected] 64. Nandhini Singh IIT BHU, Varanasi [email protected] 65. Vikas Shivam IIT BHU, Varanasi [email protected] 66. K Siva Prasad NIT Trichy [email protected] 67. Kumaran NIT Trichy [email protected] 68. Vinod Kumar MNIT Jaipur [email protected] 69. Ornov Maulik MNIT Jaipur [email protected] 70. Jatin Bhatt VNIT Nagpur [email protected] 71. Satish Idury VNIT Nagpur [email protected] 72. R Koteswara Rao University of Hyderabad [email protected] 73. G Ramya Sree University of Hyderabad [email protected] 74. Akanksha Dwivedi University of Hyderabad [email protected] 75. Abhijit University of Hyderabad [email protected] 76. J Babu Rao Andhra Univ., Vizag [email protected] 77. KR Ravi PSG Tech [email protected] 78. J Nagalakshmi RGUKT, Basara [email protected] 79. Mohan Murali RGUKT, Nuzvid [email protected] Krishna m

80. K Praveen Kumar R.V.R & J.C College of [email protected] Engg. Guntur 81. S Kumar ARCI, Hyderabad [email protected] 82. Amit Srivastava BARC, Mumbai [email protected] 83. Sankara DMRL, Hyderabad [email protected] Subramanian 84. Bhaskar Majumdar DMRL, Hyderabad [email protected] 85. R Ramakrishnan DMRL, Hyderabad [email protected] 86. Joysurya Basu IGCAR, Kalpakkam [email protected] 87. S Abhaya IGCAR Kalpakkam [email protected] 88. Jayaraj IGCAR Kalpakkam [email protected] 89. M Vijayalakshmi IGCAR, Kalpakkam [email protected] 90. S Raju IGCAR, Kalpakkam [email protected] 91. A Sasikumaran IGCAR Kalpakkam [email protected] 92. Chiranjit Poddar IGCAR Kalpakkam [email protected] 93. R Mythili IGCAR Kalpakkam [email protected] 94. Alphy George IGCAR Kalpakkam [email protected] 95. Chanchal Gosh IGCAR Kalpakkam [email protected] 96. Raj IGCAR Kalpakkam [email protected] Narayan Hajra 97. K Sridhar NMRL, Ambarnath [email protected] 98. S Gowtam NMRL, Ambarnath [email protected] 99. Vivek Srivastava NMRL, Ambarnath [email protected] 100. Somnath TIFR, Mumbai [email protected] Bhattacharya 101. Amit Salvi TRDDC, Pune [email protected] 102. Govind VSSC, Trivandrum [email protected] 103. Bala K Bharadvaj Boeing India, Bangalore [email protected] 104. Om Prakash Boeing India, Bangalore [email protected] 105. K Anand GE, Bangalore [email protected] 106. Sanjay Vaidya Hysitron, Bangalore [email protected] 107. Hemant Gourkar Anton Par hemant.gourkar@anton- paar.com 108. Verghese Mammen Anton Par verghese.mammen@anton- paar.com

Organising Committee

Chairman Prof M Kamaraj Convener Prof BS Murty Co-Convener Dr Ravi Sankar Kottada Members Prof KC Hari Kumar Dr Srinivasa Rao Bakshi Dr Chinmoy Chattopadhyay Mr Guruvidyarthi Ms Ameey Anupam Ms R Lavanya Mr Adil Shaik Mr Anil Prasad Mr K Anoop Mr R Anand Shekar