Model of nanoindentation size effect incorporating the role of elastic deformation

Based on the classical Nix-Gao model of indentation size effect (ISE), a new model incorporating the role of elastic deformation is proposed for modeling ISE at indentation depths below 100nm. We show that, while elastic deformation is generally not associated with the generation of geometrically necessary dislocations (GNDs), neglecting it can lead to severe overestimation of both the nanoindentation hardness and GND density at small indentation depths, particularly below 100 nm, and the reverse ISE is also described. In this sense, elastic deformation can play an essential role in estimating nanoindentation hardness at small indentation depths. It is shown that our model predictions are in good agreement with experimental results on nanoindentation of single Cu and MgO crystals. A similar model applied to ISE in ion-irradiated metallic materials, where the irradiation hardening effect and ISE are successfully separated, enables analysis of irradiation hardening in ion-irradiated metallic materials without the interference of ISE. (C) 2019 Elsevier Ltd. All rights reserved.