Dr. Liang Qi, Assistant Professor in Materials Science & Engineering Department at University of Michigan will give a seminar titled "Design refractory complex concentrated alloys with enhanced strength, ductility and corrosion resistance" to the interested faculty and students at Discovery Park.

Abstract

Body-centered cubic (bcc) refractory complex concentrated alloys (RCCAs) are of great interest due to their remarkable strength at high temperatures. Optimizing the chemical compositions of these alloys to achieve a combination of high strength, room-temperature ductility, and high-temperature corrosion resistance remains challenging. We first analyzed the electronic structures of defects in BCC refractory alloys. A general linear correlation can be found between two descriptors of local electronic structures at defects in pure metals and the solute-defect interaction energies in binary alloys of refractory metals with transition-metal substitutional solutes. This linear correlation plus a residual-corrected regression model provides quantitative and efficient predictions on the solute-defect interactions in alloys. In addition, with these local/global electronic descriptors and a simple bond-counting model, we developed regression models to accurately and efficiently predict the unstable stacking fault energy (γusf) and surface energy (γsurf) for RCCAs. Using the regression models, we performed a systematic screening of γusf, γsurf, and their ratio in the high-order multicomponent systems to search for alloy candidates that may have enhanced strength-ductile synergies. Then we develop hierarchical screening models to identify promising alloys from a 13-element composition space (Ti-Zr-Hf-V-Nb-Ta-Mo-W-Re-Ru-Al-Cr-Si). Density-functional theory (DFT) calculations are implemented to calculate γusf and γsurf for ∼140 binary, ternary, and quaternary alloys, followed by rapid screening over quaternary alloys using physics-based regression models. The results combined with high-throughput thermodynamics calculations are used to discover promising bcc alloys with high ductility, thermodynamic stability at least at 800 ℃, and thermodynamic capability to passive oxide films. Finally, laser powder bed fusion (L-PBF) processing is applied to two representative RCCAs, which show promising results in both yield strengths and failure tensile strains.

Biography

Dr. Liang Qi joined the Department of Materials Science and Engineering at University of Michigan as an Assistant Professor in Winter 2015 and was promoted to Associate Professor in Sep 2021. He studied Materials Science and Engineering at Tsinghua University in China and got his bachelor’s degree in 2003. He earned his master's degree in Department of Materials Science and Engineering at the Ohio State University in 2007 and his doctoral degree in materials science and engineering at University of Pennsylvania in 2009. From 2009 to 2012, he worked as a postdoctoral research fellow at UPenn and Massachusetts Institute of Technology. Between 2012 and 2014, he worked as an assistant project scientist at University of California, Berkeley. His research fields are investigations of the mechanical and chemical properties of materials by applying theoretical and computational tools, including first-principles calculations, atomistic simulations, multiscale modeling and machine learning. He received the NSF CAREER award in 2019 and 2021 TMS Materials Processing & Manufacturing Division (MPMD) Young Leaders Professional Development Award.