Abstract
Indentation technique is used as one of the evaluation methods of material on microscopic region. But this method shows the shallower the indenter presses, the harder the result of a measurement. This is called as size effect of hardness. The strain gradient theory is studied on this problem. In this study, observation by EBSD(Electron Back Scatter Diffraction) were done around several sized indentations and crystal orientations were measured. The direction of expanse of the plastic region was different and it was found that the slip direction affects it. And it was found that the relative plastic region size to the maximum indentation depth decreased when the maximum indentation depth became extremely small and when the tip of indenter was dull. Provided that the strain near the indentation is same, the strain gradient increase if the plastic deformation region decrease. So, many GN dislocations, which prevent atoms from moving, occur and material becomes harder.
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