Microstructural stability during long-term natural storage and tensile deformation of nanograined FCC pure copper and HCP pure zirconium

Abstract

The microstructural stability during long-term storage and tensile deformation have been investigated for nanograined (NG) pure Cu and pure Zr produced by severe plastic deformation. Abnormal and uniform grain growth behaviour is observed in the NG Cu after long-term storage and tensile deformation at different strain rates, respectively. The abnormal grain growth during long-term storage is related to the relaxation of the fluctuating microstrain in the deformed microstructure and can be accelerated by increasing the temperature. The uniform grain growth during tensile deformation is dominated by grain boundary (GB) migration due to the absorption of dislocations. The degree of GB migration in the case of a low strain rate is relatively large owing to the dynamic equilibrium between the formation and disappearance of dislocations. However, the GB migration at a high strain rate is suppressed by the piled-up dislocations. In comparison, the NG Zr exhibits relatively high microstructural stability with no obvious grain growth during long-term storage and tensile deformation. This is attributed to the difference in the crystal structure between Cu and Zr.