Special Seminar

October 12, 2023

11:00 a.m. ET

Mehl Room, Wean 2325

Design and thermomechanical processing of microstructurally flexible TRIP HEAs and refractory element based CCAs

The advent of high entropy alloys (HEAs) nearly two decades ago generated tremendous interest among researchers worldwide. Further, the opportunity to play around with the composition in the non-equiatomic space and develop various complex concentrated alloys (CCAs), has kept researchers intrigued in recent years. The present study explores the microstructure-processing-property relationships in two types of multi-principal element alloys (MPEAs).

The first part of the study focuses on transformative HEAs exhibiting unique “flexible microstructures”, resulting from the combined effect of alloy chemistry and friction stir processing (FSP). A series of Fe-Mn-Co-Cr-Si- based alloys were systematically designed, encompassing single phase fcc or dual-phase fcc-hcp microstructures in the as-cast state. 

Further microstructural tailoring was performed by the synergistic application of strain, strain rate and temperature during FSP. The extent of transformation induced plasticity (TRIP) is intricately associated with the fcc to hcp epsilon martensitic transformation during FSP or subsequent tensile deformation. In a few cases, conventional rolling and annealing treatments were also carried out to study other mechanisms such as precipitation and twinning. A comprehensive investigation of various alloys outlined the importance of activating multiple deformation mechanisms including TRIP, pyramidal <c+a> slip and deformation twinning in the hcp phase, to achieve high work hardening characteristics underlying a high strength-ductility combination.

The second type of alloys include refractory metal based CCAs. Fe-Cr-Mo-Nb-Ti and Fe-Cr-Mo-Nb-Ti-Zr based alloys were fabricated through vacuum arc melting and heat treatment used to tailor a microstructure consisting of bcc solid solution and Laves phases. The objective is to develop novel biomedical alloys with low density, high strength and corrosion resistance, while maintaining compatible elastic modulus and biocompatibility. Ongoing research work is focused on balancing strength and elastic modulus through alloy design, fine-tuning the microstructure by thermomechanical processing to retain sufficient ductility and exploring microstructure dependence of corrosion behavior and biocompatibility.

Dr. Subhasis Sinha, Department of Metallurgical Engineering, Indian Institute of Technology (BHU) Varanasi

Dr. Sinha completed his BE in 2007 and was the recipient of Sankar Das Memorial Silver Medal in his undergraduate studies at the Department of Metallurgical and Material Engineering, Jadavpur University, Kolkata. Subsequently, he obtained ME in Materials Engineering at IISc Bangalore in 2009 and MS in Materials Science at Carnegie Mellon University, Pittsburgh, USA in 2013 and also worked as a researcher at Tata Steel R&D, Jamshedpur during 2009-2011. He completed his PhD at the Department of Materials Science and Engineering, IIT Kanpur in 2017 and his doctoral thesis was on “Effect of twinning on tensile and cyclic deformation behaviour of hexagonal close packed titanium”. Then, he worked as a postdoc for 2 years at the Department of Materials Science and Engineering, University of North Texas, Denton, USA, in the field of friction stir processing of transformative high entropy alloys and copper based immiscible alloys. He joined the Department of Metallurgical Engineering, IIT (BHU) Varanasi as an Assistant Professor in September 2019. He has co-authored 40 publications, 1 patent and delivered 13 oral presentations at various international conferences. He was the recipient of the ASM-IIM Visiting Lectureship Award 2022 (Below 40 Years category), with which he is currently visiting the United States.

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