A micromechanics-based model for shear-coupled grain boundary migration in bicrystals

A complete micromechanics-based model is here proposed using the concepts of continuum kinematics and thermodynamics. A new constitutive framework is proposed to describe stress-induced “shear-coupled” grain boundary (GB) migration. Like non diffusive phase-transformations, shear-coupled GB migration can be considered on the thermodynamics point of view of conservative nature until high temperature with respect to melting point (i.e., diffusionless but thermally activated). The micromechanics-based continuum model can include intra-crystalline slip, GB sliding and shear-coupled GB migration as additive dissipative mechanisms. To illustrate the present theory, the model is applied to shear-coupled GB migration in the case of three “flat” Cu bi-crystals [0 01˙] with symmetric tilt GB (STGB): ΣΣ17(410) (θ=28.07°θ=28.07°), Σ5(210)Σ5(210) (θ=53.13°θ=53.13°), ΣΣ41(540) (θ=77.32°θ=77.32°). Molecular dynamics (MD) simulations under simple shear loading are first performed to identify the active shear coupling modes, the stick–slip behavior at 0 K and 500 K and the bicrystal finite size dependence on the shear stress responses. The results of the micromechanical model are discussed in comparison with MD simulations. The effects of anisotropic vs. isotropic elastic properties on effective elastic shear moduli, overall shear stress drop magnitudes and dissipated energy during GB migration are analyzed for these STGB.

► A constitutive model is developed to describe shear-coupled grain boundary migration. ► Molecular dynamics simulations are investigated for three Cu[0 0 1] symmetric grain boundaries. ► The migration modes and critical stresses are identified by molecular dynamics simulations. ► The effective elastic moduli and the shear stress drops during migration are studied in the light of the micromechanical model.