Effects of nano-scale grain boundaries in Cu on its Bauschinger's effect and response to cyclic deformation

Influence of nano-scale grain boundaries (GB) on the mechanical behavior and Bauschinger's effect in copper during cyclic loading, in comparison with those of Cu single crystal (SC) and Cu with nano-scale twin boundaries (TW), was computationally investigated employing the molecular dynamics simulation technique. It was shown that Bauschinger's effect in the nano-systems was gradually weakened in the following order: SC, GB and TW. The annihilation of dislocations or partial dislocations with opposite signs and the shrinkage/extension of associated stacking faults upon stress reversal were mainly responsible for Bauschinger's effect in the nano-copper systems. The cyclic loading process increased the failure strain of the GB, TW and SC systems. However, the increase in the failure strain was less profound in the GB and TW systems. This could be attributed to the fact that both the grain and twin boundaries can block the dislocation movement and stacking fault extension, resulting in higher stress concentration at the boundaries to promote failure.