Thermodynamics of translational states in the Sigma 3 grain boundary system.

Abstract

The structure and symmetry of grain boundary translational states in the Σ3 {110}//{111} and {110}//{112} bicrystals are reported. Symmetry-dictated extrema in interfacial energy with respect to "in-plane" translation are found. Atomic level calculations are performed to construct a complete y surface for the cell of nonidentical displacements of the system. The thermodynamics of interfaces is extended to include translation as a degree of freedom. The conditions of equilibrium between translational states are then investigated. These conditions in conjunction with the γ surface are used to explain experimental observations of translational states along boundaries in the Σ 3 system. It is shown that under certain constraints, segments of boundary which are unstable with respect to translation may exist. This is consistent with experimental observations.