Misorientation-dependent transition between grain boundary migration and sliding in FCC metals

Grain boundaries (GBs) play a crucial role in the mechanical behaviors of nanocrystalline ma-terials. The dynamics of GBs depend on a variety of intrinsic and extrinsic factors, including GB misorientation, inclination, curvature, metal type and loading history. Controlling GB geometry and deformation behavior thus provides effective means to tailor the mechanical properties of nanostructured materials. However, the relationship between deformation mechanism and GB geometry is still lacking, largely due to the vast amount of metastable GB structures and defor-mation paths. Here, the relation between GB misorientation (theta, a critical degree of freedom for GB structure) and GB deformation mechanisms was studied by large-scale molecular dynamic simulation in face-centered cubic (FCC) metals. With increasing GB misorientation, the GB deformation mechanism transitions from migration to sliding and further to migration again. The critical transition thresholds (critical misorientations) vary with metal types. An energetic model that links deformation mechanism with GB structure was further developed with a focus on predicting the critical GB misorientation at which GB sliding supersedes GB migration. The in-fluence of metal type on the transition threshold is well captured. We finally extend this model to general GBs with complex atomic structures and compare the theoretical predictions with data reported in the literatures and obtained from the present work. Our findings shed lights on the misorientation-dependent GB deformation mechanisms and can be utilized in GB engineering that pursues high-performance nanocrystalline metals.

Automated summary

Grain boundaries play a crucial role in the mechanical behaviors of nanocrystalline materials, and their deformation mechanisms are closely related to grain boundary misorientation. In this study, the relationship between grain boundary misorientation and deformation mechanisms was investigated through large-scale molecular dynamic simulations in face-centered cubic metals. An energetic model was developed to predict the critical grain boundary misorientation at which grain boundary sliding surpasses grain boundary migration.