Multiscale modelling of MgO plasticity

We propose a multiscale model of plasticity of pure MgO single crystals. The core structure of the rate controlling ½〈1 1 0〉 screw dislocations has been modelled by the Peierls–Nabarro–Galerkin method. This model relies on γ-surfaces calculated ab initio for the {1 1 0}, {1 0 0} and {1 1 1} planes. The ½ 〈1 1 0〉 screw dislocations spread mostly in the {1 1 0} planes. The Peierls friction values are 150 MPa and 1.6 GPa for glide on the {1 1 0} and {1 0 0} planes, respectively. The kink pair theory is applied to model thermal activation of dislocation glide over the Peierls barrier below the athermal temperature Ta and to build a velocity law for this regime. The critical resolved shear stresses are deduced below Ta from the Orowan law. Above Ta the athermal stress τμ is obtained from discrete dislocation dynamics simulations to account for dislocation–dislocation interactions. This model is found to satisfactorily reproduce the critical resolved shear stresses observed experimentally, provided the contribution of impurities (unavoidable in experiments) is subtracted.