Shear direction induced transition mechanism from grain boundary migration to sliding in a cylindrical copper bicrystal

Control over grain boundary (GB) motion ways provides an effective mean for tailoring the mechanical and physical properties of nanocrystalline metals. However, shear direction induced transition from GB migration to sliding in nanocrystalline metals has remained elusive. In this work, we used molecular dynamics (MD) simulations to track the dynamic process of a representative Sigma 11(113) high-angle GB in a cylindrical copper bicrystal under controllable shear directions parallel to the GB plane. When the shear direction changed from the [332(-)] direction to the [11(-)0] direction (the shear angle. increased from 0 degrees to 90 degrees), the dominant GB deformation mechanism switched from GB migration to sliding. The critical orientation (critical shear angle) of the transition was [85(-)1(-)] (75 degrees). Atomistic observations indicated that the disconnection and the surface step nucleation provoked the GB migration and sliding, respectively. This shear direction induced transition was also found in other < 110 > symmetrical and asymmetric tilt GBs, as well as nano polycrystalline metals. Analytical models revealed that the transition mechanism originated from the competition between the nucleation energies of the disconnection and surface step. These insights may contribute to the ongoing search for favoring manageable design of nanocrystalline metals by GB-mediated plastic deformation.

Automated summary

Studies have found that the change in shear direction can cause a transition from grain boundary migration to sliding in nanocrystalline metals. This transition is caused by the competition between the nucleation energies of disconnection and surface step.