报告题目： Structure and properties of micronanoscaled materials

报 告 人： 单志伟，Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano) & Hysitron Applied Research Centre in China (HARCC), State Key Laboratory for Mechanical Behaviour of Materials, Xi’an Jiaotong University, Xi’an, China

报告时间：2013年12月11日(周三) 上午10：00 – 11：30

报告地点：清华—富士康纳米科技研究中心四楼报告厅

报告摘要：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.