报告题目(中文)：利用纳米压痕技术研究晶体材料的初始塑性和位错形核
报告题目(英文)：Studying incipient plasticity and dislocation nucleation in crystalline solids using nanoindentation techniques

报告时间：2014-05-05 10:00

报告地点：延长校区材料所3楼会议室

报告人单位：田纳西大学材料科学与工程系

报告内容简介：We recently performed nanoindentation tests on single-crystal Mo and Ni, and a coarse-grained, high entropy FeCoCrMnNi alloy to investigate the nature of the onset of yielding. In the case of single crystals, the critical shear stress for the first pop‐in was ~1/7 of the shear modulus in both crystals. The dependence of pop‐in probability on load was understood in terms of a thermally activated dislocation nucleation process. A comparison of the activation energies suggests nucleation of full dislocations in BCC-Mo and partial dislocations in FCC‐Ni. In the case of high‐entropy FCC‐FeCoCrMnNi alloy, we found that the maximum shear stress required to initiate plasticity was within 1/15 to 1/10 of the shear modulus and relatively insensitive to grain orientation. The stress was strongly dependent upon the temperature, indicating a thermally activated process. Using a statistical model developed by Schuh et al, both the activation volume and activation energy were measured and further compared with existing dislocation nucleation models. It appeared that a mechanism consisting of a heterogeneous dislocation nucleation process with vacancy‐like defects (~3 atoms) as the rate-limiting nuclei was dominant.

报告人简介(中文)：T.G. Nieh教授田纳西大学材料科学与工程系 教育经历斯坦福大学获得材料科学与工程博士学位华盛顿大学获得物理学硕士台湾国立成功大学获得物理学学士 工作经历 1980-1992，洛克希德导弹与航天公司（现在为洛克希德－马丁公司），实验室资深研究员 1992-2004，劳伦斯利弗莫尔国家实验室，资深研究员 2004年8月-今，田纳西大学材料与工程系，教授 PUBLICATIONS Nieh教授与他人合作，在材料和材料相关的领域发表了超过400篇的学术论文。他撰写的教材《金属和陶瓷的超塑性》在剑桥大学出版社出版。他的主要研究领域为材料的力学性能，包括了高熵合金、金属玻璃、纳米晶材料、超塑性和超塑成形、轻金属铝和镁合金、金属基复合材料、金属间化合物、超高温合金、生物陶瓷、薄膜和纳米层片材料。 社会兼职美国TMS和ASM会员自2003年以来，成为ISI高引用材料科学家，引用次数超过10,000，H指数55 现在担任Intermetallic是杂志的主编 2009-2013担任Materials Letters杂志的主编多个专业协会的委员会成员块体非晶合金国际研讨会的组织者
报告人简介(英文)：Professor T.G. Nieh Department of Materials Science and Engineering, University of Tennessee EDUCATION PhD in Materials Science and Engineering, Stanford University. MS in Physics, University of Washington in Seattle. BS in Physics, National Cheng–Kung University in Taiwan. PROFESSIONAL EXPERIENCE Lockheed Missiles and Space Co. (now Lockheed-Martin), 1980-1992, as Senior Member of the lab. Lawrence Livermore National Laboratory, 1992-2004, as Senior Fellow Professor, Materials Science and Engineering, University of Tennessee, from August 2004-present. PUBLICATIONS Dr. Nieh has co–authored over 400 technical papers in a broad range of materials and material–related fields. He wrote a textbook "Superplasticity in Metals and Ceramics" published by Cambridge University Press. His main interest is the mechanical behavior of materials, include high-entropy alloys, metallic glasses, nanocrystalline materials, superplasticity and superplastic forming, lightweight aluminum and magnesium alloys, metal-matrix composites, intermetallics, ultrahigh temperature alloys, bioceramics, thin films and nanolaminates. SYNERGISTIC ACTIVITIES Society Fellow, TMS and ASM ISI Highly-cited Materials Scientist, since 2003. Citation no. over 10,000, H-index 55. Editor-in-Chief, Journal of Intermetallics, now. Editor, Materials Letters, since 2009-2013. Committee members of several professional societies Organizer of International Conferences on Bulk Metallic Glasses series