Indentation size effect: Reality or artefact?

The purpose of this investigation was to study the load dependence of the microhardness, typically in the range 5-500 gf. This well known phenomena is called the indentation size effect (ISE) and was investigated for two sets of specimens: titanium and aluminium alloys. Variation of the hardness with applied load was first compared with various existing models and the surface profile, near the indent, was measured by confocal microscopy. The formation of pile-ups near the indentation print led to the correction of the indent diagonal which is found to fit well with our experimental data as well as with other results in the literature. For the materials investigated, the ISE effect is an artefact, i.e. the variation of hardness with the applied load is only a consequence of the variation of the contact surface between the specimen and the indenter.