Intrinsic structural transitions of the pyramidal I <c + a> dislocation in magnesium

The stability of a mixed <c + a> dislocation on the pyramidal I plane in magnesium is studied using molecular dynamics simulations. The dislocation is metastable and undergoes a thermally-activated transition to either a sessile, basal-dissociated <c + a> or a sessile basal-dissociated <c> dislocation plus an <a> dislocation. The transition is intrinsic to pure magnesium and occurs with an energy barrier of ∼ 0.3 eV. The transformed structure is also consistent with experimental evidence in Ti and Zr, where pyramidal I slip is more prevalent. Enhancing the ductility of magnesium by stabilizing <c + a> slip on pyramidal I planes thus appears unlikely to be viable.