Topic: Atomic Transport in Crystalline Alloys in Extreme Environments

Speaker: Dr. Shen J Dillon
           Associate Professor
           Department of Materials Science and Engineering
           University of Illinois Urbana-Champaign

Abstract：

Conventional materials tend to fail in extreme environments where combinations of high strain, strain rates, particle fluxes, temperatures, and corrosive environments exist and where non-equilibrium processes may dominate.  Such environments are often inherent to next-generation systems for generating, converting, storing, and utilizing clean energy efficiently.  Materials engineered to survive in such environments often exploit nanostructuring, which is usually generated under highly non-equilibrium conditions.    Unfortunately, understanding and controlling atomic motions and microstructural evolution under highly non-equilibrium conditions remains an ongoing challenge for materials scientists.  This talk specifically focuses on developing an improved understanding of the nature of atomic motions during severe plastic deformation and draws some comparisons to other highly non-equilibrium systems such as those irradiated by particle fluxes.

Severe plastic deformation increasingly finds applications in the production of nanostructured materials with novel properties for applications in energy storage materials, energy conversion materials, or structural materials.  Different alloy chemistries respond to this processing in diverse manners and the fundamental processes controlling the microstructural and chemical evolution remain poorly understood.  Severe plastic deformation of crystalline alloys results from the summation of a large number of dislocation transport events, many of which include dislocation transport in and across interfaces.  When these events occur in sufficiently large numbers, the nature of the thermochemical interactions between solute, dislocations, and the interfaces can dominate the microstructural evolution and the final phase distribution in the sample, even at cryogenic temperatures.  We utilize model experiments to show how such interactions lead to the self-organization of complex nanostructures. At high temperatures competing thermodynamic relaxations occur via vacancy motion.  Here, we investigate the role of non-equilibrium vacancies in this process and use model experiments to quantify their concentration and production rate under shearing.  Overall, the results provide new insights into how to process novel nanostructured materials and the crucial role of non-equilibrium processes in dominating the materials response.

Brief Introduction

Shen J. Dillon is an Associate Professor in the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign. He received his B.S. and Ph.D in Materials Science and Engineering from Lehigh University in 2007.  He worked as a Research Associate at Carnegie Mellon University and a Visiting Research Scientist at the Massachusetts Institute of Technology.  He joined the faculty at the University of Illinois at Urbana-Champaign in 2009.  He is the author of over 60 journal articles.  He was a recipient of the 2011 Department of Energy Early Career Award, the 2013 National Science Foundation CAREER Award, and the 2015 American Ceramic Society’s Robert L. Coble Award for Young Scholars.