Seminar Speaker: Rajiv Mishra, University of North Texas

Deformation Induced Transformation: Revisiting Burgers Triangle with Metastability Engineered Alloys

Abstract

Transformative complex concentrated alloys (CCAs) provide opportunities for tunable performance by manipulating deformation mechanisms. We have studied Fe-Mn-Co-Cr-Si-Cu-V alloys that exhibit a combination of phase transformation and twinning. The Burgers triangle depicts the deformation-induced transformation pathways among FCC, HCP and BCC crystal structures. Early studies were limited to a few elements and dilute alloys that have intrinsic allotropic phases in the temperature-pressure phase stability map. Iron is a particularly interesting element as it has temperature-dependent FCC-BCC transformation and pressure-dependent BCC-HCP transformation. Metastability engineering of Fe-Mn-Co-Cr-Si-Cu-V CCAs shrinks the FCC-HCP-BCC transformation domain in the temperature and pressure ranges that are easily accessible experimentally with conventional mechanical testing methods. These alloys give greater flexibility for tailoring transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). In addition to the TRIP and TWIP effects, there are intriguing observations of c/a ratio evolution in the HCP phase as a function of strain. The tunable nature of these alloys opens up the possibility of designing hierarchical activation of deformation mechanics to explore plasticity-related phenomena. These aspects will be reviewed and the differences from conventional alloys will be highlighted.

Biography

Dr. Rajiv Mishra (Ph.D. in Metallurgy from the University of Sheffield) is a University Distinguished Professor at the University of North Texas. He serves as the Director of the Advanced Materials and Manufacturing Processes Institute (AMMPI) at UNT. He is also the Director of the graduated NSF I/UCRC for Friction Stir Processing and a Fellow of ASM International. He is a past chair of the Structural Materials Division of TMS and served on the TMS Board of Directors (2013-16). He has authored/co-authored 441 papers in peer-reviewed journals and proceedings and is the principal inventor of four U.S. patents. His current Google Scholar h-index is 82 and his papers have been cited more than 35000 times. He has co-authored three books; (1) Friction Stir Welding and Processing, (2) Metallurgy and Design of Alloys with Hierarchical Microstructures, (3) High Entropy Materials: Processing, Properties, and Applications. He has edited or co-edited fifteen TMS conference proceedings. He was an associate editor of Journal of Materials Processing Technology and serves on the editorial board of Materials Science and Engineering A, Science and Technology of Welding and Joining, and Materials Research Letters. He is the founding editor of a short book series on Friction Stir Welding and Processing published by Elsevier and has co-authored seven short books in this series. He is a recipient of TMS-SMD Distinguished Scientist Award in 2020.