Low temperature creep of nanocrystalline pure copper

Tensile creep of nano-grained pure Cu with an average grain size of 30 nm prepared by electrodeposition technique has been investigated in the temperature range 20–50°C (0.22–0.24 Tm). The steady state creep rate is found to be proportional to the effective stress σe=(σ−σ0), where σ is the applied stress, and σ0 is the threshold stress. The activation energy for the creep is measured to be 0.72 eV, which is close to that for grain boundary diffusion in nano-grained Cu. The creep rates are found to be of the same order of magnitude as those calculated from the equation for Coble creep. The existence of threshold stress implies that the grain boundaries do not act as perfect sources and sinks of atoms (or vacancies). The results suggest that the creep can be attributed to the ‘interface controlled diffusional creep’.