Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : October 07, 2017 - October 09, 2017
Indentation technique is one of the evaluation methods of material on microscopic region. However, size effect of hardness becomes a problem. Geometrically necessary (GN) dislocations are thought as one of the cause of this effect. The purpose of this study is to investigate the cause of size effect of hardness by evaluating density of GN dislocations. This study used Ni single crystal, having the surface crystal orientation of (0 0 1) and (1 1 1). Indentation test was performed to these planes on various indentation depths by indenters with different ridge angles, and measured density of GN dislocations around the impression. The hardness was same, but high GN dislocation area was different by (0 0 1) and (1 1 1). There was high GN dislocation area around the impression on (0 0 1), but high density area of GN dislocation was made below the impression on (1 1 1). Furthermore, the angle of indenter varied the value of size effect on (0 0 1). Smaller angled indenter made high GN dislocation area, so the angle of indenter affected the size effect. By measuring GN dislocation area, it was clarified that hardness had relation to density of GN dislocation on (0 0 1), while not on (1 1 1). Therefore, it is conceivable that the cause of size effect is storing GN dislocations around impression on (0 0 1), and relation of position between high density area and indenter on (1 1 1).
