Deformation of copper single crystals to large strains at 4.2 K - I. Mechanical response and electrical resistivity

The deformation of Cu single crystals at 4.2 K was studied by simultaneous measurements of mechanical and electrical properties. The aim was to extend the study of low-temperature deformation to higher strains than are usually employed; thus most of the crystals were stretched to failure. The deformation can be divided into three distinct regions. In region A (which includes stages I and II of plastic deformation) the crystal deforms by slip. In region B there is twinning but no slip; at the end of region B the specimen is 70% twinned. The crystal enters region C as a fine layer structure consisting of twin and parent lamellae; in this region there is no more twinning and deformation proceeds by slip. Examination of the deformation-induced resistivity and resistivity annealing confirms the conclusion that flow stress in region A is due to dislocation accumulation and indicates that in region C other obstacles, such as twin-parent interfaces, are also important. The annealing data, together with other evidence, suggest that elimination of short vacancy dipoles and loops by pipe diffusion accounts for the recoverable component of the resistivity.