Influence of local microstructure on the dislocation transference and micro-mechanical response in metastable fcc alloy

摘要

This work underscores the effect of local microstructural configuration on the dislocation movement and micro-mechanical behaviour in fine/ultra-fine-grained (< 2 mu m), cold-rolled, and annealed 301L austenitic stainless steel by site-specific nanoindentation experiments. Indentation loading, holding, and unloading behaviour have been studied separately for five different microstructural categories. Hardness and modulus vary proportionally from one indentation to another. It has been observed that a large density of high-angle boundaries most competently restricts the dislocation motion (strain hardening) resulting in high hardness. However, the back stress generated by the dislocation pile-up aids recovery during holding/unloading. Contrarily, the coarse grain reveals lower hardness attributed to easy dislocation transmission and a lesser elastic recovery during holding/unloading owing to an insufficient back stress in the absence of a favourable dislocation pile-up. The observation is against the general expectation considering the grain size dependence of the formation of pile-ups in ductile materials subjected to large-scale deformation. Interestingly, low-angle boundaries interact more with the dislocations and form such a defect structure that the strain locally reaches the critical value for the formation of deformation-induced martensite following Kurdjumov-Sachs orientation relationship with the parent austenite.