Model for the characterization of indentation size effect by quantitative analysis of surface roughness

Abstract

An increase in hardness with decreasing indentation depth, the well-known indentation size effect (ISE), has been observed in numerous nanoindentation experiments. This increase is believed to be an intrinsic material response associated with the geometrically necessary dislocations induced by indentation. In addition, however, there are extrinsic ISE factors such as tip bluntness, surface roughness, oxide layer, work-hardened layer, chemical contamination, etc. In particular, specimen surface roughness is an inevitable extrinsic factor in the ISE. This issue is critical in the ISE characterization of nano/micromaterials where the indentation depth is limited, and must be considered in order to achieve precise ISE characteristic values using nanoindentation. An ISE model taking into account surface roughness was developed by dividing the indentation energy into the energy to flatten a rough surface corresponding to the contact area and the energy to deform a flat surface. The energy to deform the flat surface was related to the ISE model by considering the rounded tip effect; thus, both tip blunting and surface roughness effects were taken into account.