简介: |
Micronanoscale refers to the size regime ranged from 10 nm to 10,000 nm. Compared with the relative mature knowledge system in the macro regime (>10,000nm) and quantum regime (<10nm), the knowledge system for the materials properties at this size regime are still under developing and therefore represent a“rich ore” for both science and technology. In this talk, I will first give a brief review on the most recent developments of the state-of-the-art in situ transmission electron microscope deformation techniques and then proceed to report our applications of these techniques on micronanoscaled materials. We found that single-crystal pillars fabricated through focused ion beam always contain high density of defects. However, if the sample size is small enough, then both face-centered-cubic metals and body-centered-cubic metal pillars can experience ‘‘mechanical annealing,’’ i.e., a phenomena referring to the reduction of dislocation density in the deforming volume, when dislocation generation is outweighed by dislocation annihilation through the free surface. We also found that when the sample size was reduced below 1 micrometer or so, stress saturation and deformation mechanism transition occurred in a hexagonal-close-packed Ti alloy. Unlike crystalline materials, metallic glasses do not allow the presence and movement of dislocations or deformation twinning. However, we demonstrated the metallic glasses also follow the well-established tenet for crystalline materials: i.e., smaller is stronger and can reach its theoretical elastic limit under appropriate testing conditions. In addition, for the tested size regime, we found that high-energy electron beam has no obvious effect on the mechanical properties of materials with metallic bond. However, for materials with covalent bond and ionic bond, significant electron beam effects have been confirmed.
报告人简历:
Prof. Zhi-Wei Shan is the “Chang Jiang Professor” at Xi’an Jiaotong University, China. He received his B.S. in Materials Science and Engineering from Jilin University, China in 1996, his M.S. degree from Institute of Metal Research (IMR), Chinese Academy of Sciences (CAS) in 1999, and his Ph.D. in the Department of Mechanical Engineering from University of Pittsburgh in 2005 and then conducted postdoctoral research at National Center for Electron Microscopy (NCEM), Lawrence Berkeley National Laboratory in the emerging field of quantitative deformation tests inside TEM. In 2006, he joined Hysitron, Inc. which is known as the world leader for nanomechanical test instruments. Dr. Shan is currently the deputy dean of School of Materials Science and Engineering, Xi’an Jiaotong University. His research interests focus on applying and developing unique quantitative in situ electron microscopy techniques and revealing the novel properties of advanced nanostructural materials. He has published 40+ papers in peer reviewed journals, including Science, Nature, PNAS, Nature Materials, Physical Review Letters et al. |
