Energetic Terms Associated with Twin Nucleation in Magnesium

Molecular dynamics simulations are performed that follow the evolution of a tension twin embryo nucleating from an asymmetrically tilted grain boundary to investigate the energetics of twin nucleation. The line, surface, and volumetric terms associated with twin nucleation are identified. A micromechanical model is proposed where the stress field around the twin nucleus is estimated using the Eshelby formalism, and the contributions of the various twin-related structures to the potential energy of the twin are evaluated. The reduction in the grain boundary energy arising from the change in character of the prior grain boundary is found to offset the energy costs of the other interfaces. The defect structures bounding the stacking faults that form inside the twin are also found to possibly have significant energetic contributions. These results suggest that both of these effects could be more significant than has been assumed by many earlier continuum-scale twin nucleation models and are perhaps critical considerations when predicting twin nucleation sites in magnesium.