Indentation size effect, geometrically necessary dislocations and pile-up effects in hardness testing of irradiated nickel

摘要: Abstract The indentation size effect response, based on dislocation density, of commercially pure Ni irradiated at 120°C with 6MeV protons to 0.1dpa, was compared non-irradiated Ni. Irradiation-induced defects were characterised by TEM. Nano-scale and micro-scale tests carried out. Nix-Gao (NG) model applied determine the increase in bulk yield strength arising from irradiation induced defects, which agreed well predicted Bacon-Kocks-Scattergood (BKS) obstacle hardening model, using a superposition SFT, glissile perfect loops sessile Frank loops. A bi-linear trend observed NG both material, indicating transition deformation mechanisms for indents ‘nano-scale’ regime. extent minimized if pile-up measured accounted for. It is shown that, this care must be taken when interpreting measurements hardness due are made depths shallower than 500nm. experimentally strain gradient plasticity modelling independent SEM/EBSD analysis that there higher density geometrically necessary dislocations (GNDs) present volume under an indent material analogous material; results more confined plastic material. proposed inhibit acting as obstacles motion indenter tip being localised. result larger difference between nanoindentation testing. GND can correcting pile-up.