题目：Long-Term Defect Evolution in Iron-based Alloys from Self-evolving Atomistic Kinetic Monte Carlo Simulations

报告人：Xu Hai-Xuan，Assistant Professor

             Department of Materials Science and Engineering, 
             The University of Tennessee, Knoxville, TN, USA

时间：2015年7月20日（周一）上午9:30-11:00

地点：李薰楼468房间

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Abstract:

Radiation induced defects in structural materials for nuclear power control the microstructural evolution and changes in material properties, such as radiation-induced hardening and embrittlement and void swelling. Modeling and simulations of corresponding processes and phenomena is extremely challenging, due to the involved length and time scales. For instance, the defect production occurs at femtoseconds while the subsequent interaction and evolution in microstructure could last for decades. To bridge this gap and to computationally model and predict the defect evolution over a long period while maintaining the desired accuracy, an accelerated kinetic Monte Carlo (KMC) approach, self-evolving atomistic KMC (SEAKMC), has been developed for simulating complex defect structures. Application of SEAKMC has led to the discovery of the formation mechanism of <100> loops in BCC iron, which has been mysterious for more than fifty years. The formation of <100> loops involves a distinctly atomistic interaction between two 1⁄2 <111> loops, and does not follow the conventional assumption of dislocation theory, which is Burgers vector conservation between the reactants and the product. The effects of Cr on the <100>-formation mechanism will be revealed. In addition, the long-term defect evolution of interstitial clusters with C15 Laves structure will be addressed and how these defects interact with dislocations will be discussed. These studies provide insights into defect interaction and evolution that may provide a basis to increase the radiation resistance of these materials. In addition, the unique predictive capabilities and the limitations of SEAKMC as well as its potential applications to a wide range of problems will be outlined.

Short Bio:

Dr. Xu earned his bachelor's degree in Metallic Materials Engineering from the Dalian University of Technology (China) in 2005, and his M.S. and Ph.D. in Materials Science and Engineering from the University of Florida in 2008 and 2010, respectively. His dissertation research focuses on point defect interaction and evolution as well as their effects on mechanical properties, ferroelectricity, and transport properties of materials using ab initio and molecular dynamics simulations. In 2010, Dr. Xu joined Center of Defect Physics in Structural Materials, which is an Energy Research Frontier Center at the Oak Ridge National Laboratory, as a postdoctoral researcher where he developed a new kinetic Monte Carlo method extending the time scale of traditional atomistic simulations to investigate long-term defect dynamics in advanced structural alloys. In 2013 Dr. Xu joined the faculty at the University of Tennessee and his recent research interests include defect properties and evolution in advanced alloys, two-dimensional (2D) materials, and complex oxide superlattices.

Dr. Xu has authored or co-authored ~30 technical papers and has presented ~10 invited presentations at national and international conferences.  Dr. Xu also served as reviewer or panelist for U.S National Science Foundation (NSF), U.S. Department of Energy (DOE) Nuclear Energy University Program (NEUP), Swiss National Science Foundation, and more than twenty international journals.