The effect of dislocation density on the interactions between dislocations and twin boundaries in nanocrystalline materials

The interactions between dislocations and twin boundaries (TBs) are significantly affected by both intrinsic material properties and extrinsic factors, including stacking fault energy, the energy barriers for dislocation reactions at TBs, twin thickness and applied stress. In this study, dislocation-TB interactions in grains with different dislocation densities were investigated and we conclude that the dislocation density also affects the dislocation-TB interactions. In a twinned grain with a low dislocation density, a dislocation may react with a TB to fully or partially penetrate the TB or to be absorbed by the TB via different dislocation reactions. Alternatively, in a twinned grain with a high dislocation density, dislocations tangle with each other and are pinned at the TBs, thereby making it unfavourable for further dislocation reactions to mediate dislocation penetration across the TB. This leads to an accumulation of dislocations at the TBs, raising the local strain energy, which, in turn, is released by the activation of secondary twins by partial dislocation emissions from the other side of the TB.