Twin Boundaries merely as Intrinsically Kinematic Barriers for Screw Dislocation Motion in FCC Metals.

Jiayong Zhang,Hongfei Ye,Hongwu Zhang,Yonggang Zheng

doi:10.1038/srep22893

Abstract

Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations. Though observed in both experiments and simulations, the barrier effect of TBs is rarely studied quantitatively. Here, with atomistic simulations and continuum based anisotropic bicrystal models, we find that the long-range interaction force between coherent TBs and screw dislocations is negligible. Further simulations of the pileup behavior of screw dislocations in front of TBs suggest that screw dislocations can be blocked kinematically by TBs due to the change of slip plane, leading to the pileup of subsequent dislocations with the elastic repulsion actually from the pinned dislocation in front of the TB. Our results well explain the experimental observations that the variation of yield strength with twin thickness for ultrafine-grained copper follows the Hall-Petch relationship.

Highlights

Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations
The strengthening effect is attributed to the dislocation interaction with and accumulation at TBs17, including the long-range static repulsion before the leading partial enters the TB and the kinematic impediment caused by the discontinuity of slip planes across the TBs
The new insights into the nature of TBs induced strengthening effects will considerably simplify the development of mesoscopic/ macroscopic theoretical models that take into consideration the effects of TBs on the mechanical properties of materials

Summary

Introduction

Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations. Though observed in both experiments and simulations, the barrier effect of TBs is rarely studied quantitatively. The strengthening effect is attributed to the dislocation interaction with and accumulation at TBs17, including the long-range static repulsion before the leading partial enters the TB and the kinematic impediment caused by the discontinuity of slip planes across the TBs. Though a lot of work has been done about the activation or strengthening mechanism, there are few quantitative studies about the static repulsion and kinematic impediment, especially their role in strengthening the material at different deformation stages, which is the cornerstone for predicting and designing the mechanical properties of materials with TBs. In this paper, we first studied the intrinsic interaction between screw dislocations and TBs based on atomistic simulations and continuum models. The new insights into the nature of TBs induced strengthening effects will considerably simplify the development of mesoscopic/ macroscopic theoretical models that take into consideration the effects of TBs on the mechanical properties of materials

Methods

Results

Conclusion