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

报告人:    Prof. T. G. Nieh

Department of Materials Science and Engineering, The University of Tennessee, USA

时间：2015年6月12日(周五)  10: 00         

地点：中科院力学所主楼344会议室

报告摘要：

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.

报告人简介：

T.G. Nieh is a full professor in the Department of Materials Science and Engineering, University of Tennessee, since joining in 2004. He has published over 400 journal articles in structural materials-related area, including complex alloys, metallic glasses, nanocrystalline materials, superplastic materials, lightweight alloys, refractory metal alloys, metal-matrix composites, intermetallics, bioceramics, thin films and multilayers. He is currently also Editor-in-Chief of Intermetallics. Dr. Nieh is the main organizer of a series of international conference on bulk metallic glasses. He received his doctoral degree from Stanford University and worked previously for Lockheed-Martin and Lawrence Livermore National Laboratory.

报告联系人：沈楠  (office@lnm.imech.ac.cn 82543935)