A gradient Eshelby force on twinning partial dislocations and associated detwinning mechanism in gradient nanotwinned metals

Abstract

It is well known that the driving force on dislocation glide is the Peach-Koehler force which is proportional to the resolved shear stress on the slip plane. Here, we report a type of configurational force, referred to as the gradient Eshelby force, that can drive the motion of twinning partial dislocations on twin boundaries (TBs) in the absence of any resolved shear stress and cause detwinning in gradient nanotwinned (GNT) metals, an emerging class of multiscale metallic materials with exceptional mechanical properties and novel deformation mechanisms. Specifically, we consider the Eshelby-force-driven motion of twinning partial dislocations and associated detwinning mechanism in GNT metals made of preferentially oriented TBs and columnar grain boundaries (GBs) with spatially varying twin spacing and grain size. Large-scale molecular dynamics simulations validate the proposed Eshelby-driven detwinning mechanism, where twinning partial dislocations are nucleated from GBs and glide on TBs near the region with the steepest local gradient, leading to extensive TB migration and twin annihilation. This study demonstrates the important role of Eshelby force in controlling twinning partial glide and TB migration in GNT metals, which may have broad implications on plastic deformation in gradient nanostructured metals.