主讲人：T.G. Nieh

题目：Using nanoindentation method to probe the mechanical behavior of materials in small volume

地点：材料馆101教室

主办单位： 材料科学与工程学院

开始时间：2015-6-10，10：00

持续时间：1小时

Abstract：

In this presentation, I will first briefly review nanoindentation method and what the technique can be usefully applied to explore material properties, especially in the nanometer length scale. I will, then, use the study of incipient yielding in materials as an example. In this case, we have conducted instrumented nanoindentation on metallic materials with different crystalline structures, including body-centered cubic Mo and Cr, and face-centered cubic Ni and FeCoCrMnNi high-entropy alloy to characterize the nature of incipient plasticity. Experiments were carried out over a wide range of loading rate and at high temperatures. The shear stress required to initiate plasticity was found to be within 1/15 to 1/10 of the shear modulus and relatively insensitive to crystalline structure. We also observed that the onset of yielding was dependent upon the material volume the indenter tip was sampling. As a result, the physical mechanism responsible for the incipient yielding changes with the sampling volume. Using statistical methods, we were able to extract the activation volume and activation energy for the yielding process and further compared with model predictions. Incipient yielding can be triggered by either homogeneous or heterogeneous dislocation nucleation depending upon the initial material microstructure.

Dr. T.G. Nieh is currently a professor in Department of Materials Science and Engineering at The University of Tennessee. From 1980 to 1992, he worked at Lockheed Missiles and Space Co. (now Lockheed-Martin Corporation) as a Senior Fellow of Research Laboratory. He subsequently worked at Lawrence Livermore National Laboratory as a Senior Research Fellow until he joined UT in 2004.

Nieh is a world leader in superplasticity and superplastic forming. He is also widely recognized for his work in several material science disciplines, including bulk metallic glasses, nanocrystalline materials, lightweight alloys, metal-matrix composites, intermetallics, refractory metals, bioceramics, and nanolaminates. He published over 400 papers and a textbook on “Superplasticity of metals and ceramics’ and is one of the ISI highly-cited material scientists. He is now serving as Editor-in-Chief of Intermetallics and Editor of Materials Letters, etc..

Nieh received the Ph.D. degree in Materials Science and Engineering in 1980 from Stanford University, the M.S. degree in Physics in 1976 from University of Washington, Seattle, and the B.S. degree in Physics in 1973 from National Cheng-Kung University in Taiwan.

Research Areas

Metallic glasses (amorphous alloys); Nanostructured materials; High temperature materials

Selected Awards and Honors

2004 Fellow of TMS (The Materials, Minerals, and Metallurgical Society)

1992 Fellow of ASM International (American Society of Materials)

Professional Activities

Board member of International Advisory Board on Superplasticity, and has served in a number of national review/advisory panels on materials science

Consulting Professor of Harbin Institute of Technology, China; Consulting Professor of University of Science and Technology-Beijing, China; Adjunct Professor of Cheng-Kung University, Taiwan

Advisory Board, Department of Physics and Materials, Hong Kong City University