An improved approach to decouple the indentation size effect from nanoindentation hardness of ion-irradiated samples

Ion irradiation combined with nanoindentation has been widely used to evaluate the irradiation-hardening effect of materials. Depth-dependent hardening resulting from the non-flat damage profile in heavy-ion irradiation, coupled with the indentation size effect (ISE) in nanoindentations, would further increase the complexity of the extraction of irradiation hardening. In this paper, a simple and reliable approach to decouple the indentation size effect from nanoindentation hardness was proposed based on the modified Nix-Gao model with an extended plastic zone. A hardness dependency was introduced in the indentation characteristic length as well as in the plastic zone size, so that their values will smoothly alter with increasing indentation depths and naturally reduce to the values of the unirradiated material when the indentation depth is well beyond the irradiation zone. The indentation size effect in the measured nano-hardness of ion-irradiated samples can be effectively separated out using the proposed method.