Journal of Nanomedicine & Nanotechnology

Advanced nano-mechanical characterization for better performance in structural materials

19^th International Conference on Nanotechnology and Expo

November 13-14, 2017 | Atlanta, USA

Takahito Ohmura

National Institute for Materials Science, Japan

Keynote: J Nanomed Nanotechnol

Abstract:

Nano-mechanical characterization including nanoindentation and TEM in-situ straining is a novel approach for understanding mechanisms of deformation behaviors and dominat factors of mechanical properties. This paper describes experimental works and discusses a fundamental relationship between the dislocation motion and mechanical behavior of BCC iron in nano scale. Local plasticity initiation was investigated through pop-in behavior on a load-displacement curve of nanoindentation for Fe-Si alloy. Dislocation structures underneath the indenter were observed with TEM. No dislocation exists in the case of below pop-in load while high density and multi-character dislocations are emitted right after pop-in phenomenon. These results demonstrate that micro-yielding corresponds to not only an initiation of a glide motion of preexisting dislocation but drastic nucleation/multiplication in a dislocation free region. Stress-strain curves and TEM images of dislocation structures of IF steel were obtained by TEM in-situ compression. An obvious strain softening occurs after yielding and screw dislocation density gradually increases simultaneously. The relation between dislocation density and the flow stress can be understood based on the Johnston-Gilman model. The measured stress exponent value is close to seven, which is much smaller than that in case of edge dislocation with higher mobility than screw one.

Biography :

Takahito Ohmura has completed his PhD from University of Tokyo in 1996. He is Deputy Director of Research Center for Structural Materials, National Institute for Materials Science (NIMS) and Professor of Cause of Advanced Nanomaterials Science and Engineering, Kyushu University. His research interests include: Mechanical characterization of metallic materials in nano-scale; study on a relationship between local mechanical behavior and lattice defects such as dislocation and understanding the strengthening mechanisms of macro-scale mechanical properties.