Model and experiments on strain gradient hardening in metallic glass

Hardnesses of polycrystalline metals at shallow indent depth have been observed to increase because of strain gradients. Dislocation-based strain gradient plasticity models were proposed and good agreements were obtained. Metallic glasses have been observed to exhibit shear localization behaviour similar to metals. Nanoindentation have been conducted on Vitreloy metallic glasses in this study to determine the hardness variation as a function of the indent depth. Hardnesses at shallow indent depth were observed to increase significantly and comparison of the dislocation-based strain gradient indentation model indicated disagreement. An alternate strain gradient plasticity indentation model based on cluster theory of yield for glassy metal was developed and good agreement with data was obtained. The implication of the results and analysis on strain gradient behaviour is discussed.