MAE Seminar: Self-organization of Defects in Materials Under Irradiation

Abstract: Self-organization of defects in materials can create noble physical properties with potential applications in various technological fields. Sun's group studied the physical mechanism of self-organization of helium gas bubbles in molybdenum under ion implantation, and constructed the formation window of helium gas bubble superlattice in molybdenum. The ion fluence and temperature-dependent formation of gas bubble superlattice in molybdenum was examined via both transmission electron microscopy (TEM) and synchrotron-based small angle X-ray scattering (SAXS). The formation of gas bubble superlattice is linked with specific implantation conditions, including ion fluence and implantation temperature. Both experiments and atomic kinetic Monte Carlo (AKMC) modeling indicate a three-stage formation process of gas bubble superlattice, from random bubbles to planar ordering and then to 3D superlattices, and suggest that the formation of gas bubble superlattice is due to the 1D diffusion of self-interstitial atoms. The window of gas bubble/void superlattice formation was established in terms of irradiation temperatures and helium-atomic parts per million / displacements per atom (He appm/dpa) damage levels. Sun's research advances the understanding of defect self-organization in materials in non-equilibrium states and provides an approach of managing the defect formation and transforming them from a liability into an asset in a controllable way. 

Bio: Dr. Cheng Sun is a staff scientist and principal investigator working in the Advanced Characterization and Post-Irradiation Examination (PIE) division at Idaho National Laboratory. His research areas focus on mechanistic understanding of materials performance under extreme environments, with emphasis on the manufacturing-microstructure-mechanical property relationships of fuels and materials under neutron/ion irradiation. His primary areas of experimental expertise include microstructure characterizations of irradiated materials using electron microscopy and synchrotron X-ray scattering, in-situ small-scale mechanical testing of irradiated fuels and materials, and advanced manufacturing of nuclear fuels and materials. Sun holds a Ph.D. in materials science and engineering from Texas A&M University and has authored or coauthored more than 40 peer-reviewed journal publications. He has led/participated on multiple DOE projects, including Laboratory Directed Research and Development (LDRD), Basic Energy Sciences (BES), Nuclear Energy University Program (NEUP) and Nuclear Energy Enabling Technology (NEET).