Date(s) - 09/30/2021
1:55 pm - 2:55 pm
Yongfeng Zhang, Ph.D.
Engineering Physics Department
University of Wisconsin – Madison
Dr. Yongfeng Zhang is currently an assistant professor in the Engineering Physics Department, University of Wisconsin-Madison (UWM). Before joining UWM in August 2019, he served as a staff scientist at Idaho National Laboratory, INL, where he led the Computational Microstructure Science group in the then Fuel Modelling and Simulation Department. His research interest focuses on multiscale modeling and simulation of materials aging and degradation in extreme environments such as in nuclear reactors. The topic areas include irradiation-induced damage production and evolution, defect self-organization and composition redistribution, and mechanical deformation. He is also interested in developing mechanistic models for predicting material behavior in a nuclear reactor environment, to help develop advanced nuclear fuels and materials. He has served as the PI and co-PI of multiple DOE projects from the Office of Nuclear Energy, and the Office of Science and National Nuclear Security Administration. His research outcome has led to over 80 peer-reviewed journal publications.
Irradiation by energetic particles is commonly known to produce damage (e.g., disorder) in crystalline solids. Surprisingly, irradiation has also been observed to induce ordering, including domains of aligned dislocation loops and void and gas-bubble superlattices.
This talk focuses on the formation mechanisms of nanoscale void and gas-bubble superlattices in metal and alloys under irradiation. Using rate-theory-based instability analysis and mesoscale simulations, we show that the superlattices nucleate as vacancy concentration waves that develop when the uniform concentration field becomes unstable, with the crystal structure governed by anisotropic interstitial diffusion. The superlattice properties, such as lattice constant, degree of ordering, and critical dose of formation, are dependent on irradiation condition parameters including temperature and dose rate. Interestingly, temperature and dose rate are found correlated with each other, with an equivalency between shifts in temperature and dose rate. These findings shed new light on the myth of superlattice self-organization under irradiation and provide theoretical guidance for tuning superlattice properties.