Temperature and strain rate sensitivity of ultrafine-grained copper under uniaxial compression

Uniaxial compressive experiments of ultrafine-grained (UFG) copper fabricated by equal channel angular pressing method were performed at temperatures ranging from 77 K to 573 K under quasi-static and dynamic loading conditions. Based on the experimental results, the influence of temperature on flow stress, strain hardening rate and strain rate sensitivity (SRS) were investigated carefully. The results show that the flow stress of UFG copper displays much larger sensitivity to testing temperature than that of coarse grained copper. Meanwhile, both the strain hardening rate and its sensitivity to temperature of UFG copper are lower than those of its coarse counterpart. The SRS of UFG copper also shows apparent dependence on temperature. Although the estimated activation volume of UFG-Cu is on the order of ∼10 b³, which is on the same order with that of grain boundary diffusion processes, these processes should be ruled out as dominant mechanisms for UFG-Cu at our experimental temperature and strain rate range. Instead, it is suggested that the dislocation-grain boundary interactions process might be the dominant thermally activated mechanism for UFG-Cu.