Survey of shear coupling behavior in FCC Ni and BCC Fe grain boundaries

Abstract

In this study, the shear coupling behavior of 388 FCC Ni and 408 BCC Fe grain boundaries is surveyed under a wide range of temperatures (e.g., 100 – 1000 K in Ni and 100 – 1400 K in Fe) via the recently developed ramped synthetic driving force method with free end boundary conditions. It is found that there is no universal dependence of the shear coupling behavior on temperature or driving force among the grain boundaries being surveyed, i.e., an increase in temperature or driving force may make the shear coupling factor increase, decrease, or remain unchanged depending on grain boundary type. Furthermore, a continuous change in driving force is shown to generate complex shear coupling behaviors in both FCC Ni and BCC Fe bicrystals at each temperature. Observed behaviors include both smooth changes and sharp transitions in shear coupling factor within increasing driving force. Despite this complex behavior, it is found that there is no fundamental difference in the shear coupling behavior between FCC Ni and BCC Fe grain boundaries: (1) all types of transitions in shear coupling behavior that are observed in FCC Ni are also found in BCC Fe; (2) the grain boundaries with low Σ values (e.g., Σ3−Σ11) in both Ni and Fe generally show small or zero shear coupling except for a few special grain boundaries with high symmetry. Collectively, these results highlight the complexity that must be captured to construct a general model for shear coupled grain boundary migration.