Nano Mechanical Characterization and Physical Modeling of Plastic Deformation Chapter 1: Dislocation-Grain Boundary Interaction as a Strengthening Factor

Abstract

Mechanical behaviors of metallic materials in a small scale are characterized and physically modeled based on experimental measurements and computational simulation. Local plasticity in the vicinity of a grain boundary is considered in terms of an interaction between dislocation and grain boundary. It is shown experimentally that nanoindentation technique can detect a resistance to dislocation slip transfer by a grain boundary with a geometrical or a chemical factor. Molecular dynamic simulation revealed that the geometrical effect depends on not only a misorientation but also a combination with a dislocation character. TEM in-situ straining has a great potential to measure directly a critical stress upon slip transfer as well as a dislocation reaction at a grain boundary. Another potential reaction of a dislocation absorption at a grain boundary was discussed based on both the experimental results by TEM in-situ observation and the atomistic simulation in bcc metals.

Fig. 1　SPM images of the sample surface including the GB and the indent mark. (a), (b) Gradient images of the sample surface for Σ9{221} and Σ9{114}, respectively. (c), (d) Cross-sectional profiles along the yellow line on the SPM image. The distance d between the triangle center and the GB can be measured as approximately 1 µm on (a) and (b). The length l of the side of the triangle can be measured as shown in (a). A characteristic difference in the shape of the piling up around the indent mark in (c) Σ9{221} and (d) Σ9{114} is shown by orange arrows¹³⁾.