Deformation studies of initially dislocation-free copper single crystals. I. constant strain-rate tensile tests

Abstract

Copper single crystals which appeared free from dislocations in X-ray topographs were deformed in tension. Very sharp and large yield drops, up to 70% of the upper yield stress, were observed. The lower yield stress was about 20g/mm² for all dislocation-free crystals. Lüders band propagation was observed by X-ray topography at the very beginning of plastic deformation, and this was associated with unstable flow with serrations in the stress-strain curve. The work hardening rates in the easy glide region for the dislocation-free crystals tended to be lower and the extent of the easy glide region longer than the conventional good quality crystals. The extent of shear shortened and the work hardening rate in the easy glide region increased simultaneously upon accidental deformation. No correlation was found between the upper yield stress and any crystal parameter. The magnitude of the upper yield stress was similar to that observed in low dislocation density crystals.