Nanoindentation size effect on type 316 stainless steel

Nanoindentation size effect was investigated under very low loads on type 316 stainless steel. Nanoindeniation measurements were carried out on the samples surfaces with a Berkovich, pyramidal diamond indenter applying loans in the range of 25 - 1000muN. Simultaneously, AFM images of the sample surface were recorded before and after indentation process. For type 316 stainless steel, the indentation size effect was found. The results were discussed in the terms of the model of geometrically necessary dislocations proposed to interpret, the indentation size effect. It can be seen that the square of the nanohardness, H-2, vs the inverse of indentation depth, 1/h, is linearly dependent on the indented depth in the range of 25-150nm, which, is a good qualitative agreement with the predictions of the model. However, for shallow indents, the slope of the line severely changes. Some possible mechanisms for this change were proposed.