Abstract: An improved fundamental understanding of materials performance at extreme environments far from equilibrium has become a compelling need in many important applications. I will introduce the behaviors of two different materials systems (crystals and glasses) under complex environments. I will demonstrate the seemingly different systems can be understood within the same framework by combining the transition state theory and potential energy landscape (PEL)-based atomistic modeling. In addition, by tuning surrounding environments, it is possible to alter the PEL structure, manipulate the kinetics, and thus control the materials behaviors.

In particular, the first part of this talk concerns the mechanisms of interactions between dislocations and obstacles in nuclear fuel cladding materials, under various temperatures and very wide range of strain rate conditions (from 10-6s-1—107s-1 ), which was never possible to address explicitly before. It is demonstrated that, due to a non-linear coupling behavior between thermal activation and strain rate, dislocation channeling mechanism is dominant at high temperatures and low strain rates; while defects recovery prevails at low temperatures and high strain rates. The boundary differentiating the two mechanisms is further quantified, and the hereby predicted mechanism map is validated against available experiments and simulations. In the second part of the presentation, I will discuss the performance of ZrCu-based metallic glasses at different non-equilibrium meta-stable states. It is demonstrated that deformation modes (localized vs cascade) depend on the density of local minima of the materials underlying PEL: higher density would enable more efficient energy dissipation and yield better ductility. The implications of these examples, as well as the broad impacts on other important problems, are also discussed.

Bio: Dr. Yue Fan is a Eugene P. Wigner Fellow at Oak Ridge National Laboratory, working in the Materials Science and Technology Division. He received his Ph.D. degree from Massachusetts Institute of Technology in 2013. He has received several honors, including “Young Scientist Award for Best Oral Presentation” (by 2010 Nuclear Materials Conference), “Manson Benedict Award” (2013, by MIT), and “Eugene P. Wigner Fellow” (2013, by Oak Ridge National Laboratory). His primary research interest is to provide a substantive knowledge on the microstructural evolution and performance of complex systems via predictive modeling, and thus facilitate the development of new science-based high-performance materials with novel functions and unprecedented strength, durability, and resistance to traditional degradation and failure.