Bluntness measurement of a Berkovich indenter

Abstract

Indenter blunting is inevitable in nanoindentations and results in unexpected contact properties. Both relaxation of the indentation size effects and deepening of the substrate effects under a blunted indenter cause a change of the bathtub-shaped hardness with indentation depth in a soft film on hard substrate. Thus an identification of three-dimensional morphology of an indenter apex is necessary for precise measurements of hardness in thin films. We observed an actual Berkovich indenter using an atomic force microscope (AFM). Through a quantitative analysis on the AFM image, data pairs of contact area versus contact depth were obtained; curvature radius of the apex was estimated by searching a sphere well-fitted to the indenter apex morphology. The estimated curvature radius and blunted height were 1043.9±50.9 nm and 44.4 nm, respectively. By comparing with the result from the modified Kick's law, both blunted heights were comparable each other within a 7 nm difference. This confirms validity of the direct observation method with the AFM.