Issues to consider using nano indentation on shallow ion beam irradiated materials

Ion beam irradiation is a widely used method to cause radiation damage in materials in order to study materials degradation under radiation in a laboratory setting. Nanoindentation has become an often used tool to measure the mechanical property changes due to ion beam irradiation. While the combination of ion beam irradiation and nanoindentation is a powerful tool, difficulties arise and need to be discussed in detail. This work intends to draw attention to the potential issues one might face if nanoindentation is used to evaluate radiation induced hardening, especially if compared to other mechanical tests such as yield strength from tensile tests on irradiated materials and others. In this work we focus on issues associated with size and dose effects associated with quasi static nanoindentation on shallow irradiated Cu [1 0 0] single crystal material. It is shown that on 1 μm deep irradiated material it is not possible to correlate a single dose to a specific hardness value, rather a dose range has to be considered. However, deeper indents will always sample contributions of the unirradiated material. Moreover, the correlation between the indentation hardness and macroscopic properties is not straight forward.