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Abstract

Extensive experiments and molecular dynamics simulations have shown that stress-driven grain growth can greatly contribute to enhanced dislocation emission and tensile ductility in nanocrystalline metals. However, the underlying mechanism behind this correlation remains unclear. In this work a theoretical model based on the cooperative nano-grain rotation and grain-boundary migration for grain growth is proposed to explain the enhanced dislocation emission from grain boundaries. Two partial dislocation dipoles are taken to emit from opposite grain boundaries. It is demonstrated that the joint, coupled growth behavior can indeed be achieved. The energetic characteristics and the critical stress of the emission process are analyzed. We found that under some circumstances dislocation emission is energetically unfavorable when pure nano-grain rotation or migration is operating. However, the dislocation emission process can be turned to become energetically favorable when their cooperative grain growth dominates the deformation. Moreover, the critical stress required to initiate the emission can be considerably reduced by enhancing the level of rotation, and minimized by tuning the coupling factor of the migration process. As a result, the cooperative grain growth by nano-grain rotation and grain-boundary migration can serve as a new route to enhanced dislocation emission and improved tensile ductility in nanocrystalline materials. © 2019 Elsevier B.V.