Dr. Easo George, em. Professor in the Materials Science and Engineering Department, University of Tennessee (UT) and apl. Professor in the Institute for Materials, Ruhr University Bochum, Germany, will give a seminar titled "High-Entropy Alloys: What Have We Learned and What Are Their Prospects?" to the interested faculty and students at Discovery Park.

Abstract

High-entropy alloys (HEAs) have been a ‘hot topic’ in materials science for the last two decades not least because of their potential to become next-generation structural materials. At cryogenic temperatures, they exhibit the highest fracture toughness of any material class, coupled with increasing strength and ductility with decreasing temperature unlike conventional alloys. The key deformation mechanisms responsible for this outstanding combination of mechanical properties will be discussed, along with examples of compositional tuning to optimize desirable deformation mechanisms and suppress undesirable ones. Mechanism-driven approaches for resource conservation by replacing scarce and expensive alloying elements with more abundant ones will be outlined. For applications at ultrahigh temperatures, there is growing interest in refractory HEAs with higher melting points than Ni-based superalloys. However, by comparing their tensile creep behaviors it will be demonstrated that HEAs are not competitive, at least below the melting points of superalloys. At higher temperatures, it remains to be seen whether they offer any advantages relative to conventional refractory alloys. Hurdles that need to be overcome before ultrahigh-temperature HEAs can be realized will be pointed out.

Bio

Easo George is em. Professor in the Materials Science and Engineering Department, University of Tennessee (UT) and apl. Professor in the Institute for Materials, Ruhr University Bochum, Germany. Earlier, he was the UT-ORNL Governor’s Chair for Advanced Alloy Theory and Development, and before that Director of the Center for Interphase Dominated High Performance Materials and Professor of Materials Design at Ruhr University. George earned his PhD from the University of Pennsylvania and BTech from the Indian Institute of Technology Kanpur. His expertise is in physical metallurgy and mechanical behavior and is known for the following principal discoveries and ideas: hierarchy of creep cavity nucleation sites in ferrous alloys (sulfides vs. oxides vs. carbides); mechanism of the surprising brittleness of polycrystalline Ni3Al (atomic H generated by moisture in ordinary ambient air); vacancy mechanism and a theory for the anomalous strength increase with increasing temperature in FeAl; size effects (‘smaller is stronger’) caused by the interaction of dislocation content with specimen volume in micropillars and nanoindentation; disproving the founding entropy hypothesis of HEAs regarding phase stability and mechanical properties and demonstrating that deformation-induced twinning is the main reason why they can avoid the strength-ductility tradeoff.