Highly anisotropic slip-behavior of pyramidal I 〈c+a〉 dislocations in hexagonal close-packed magnesium

In hexagonal-closed-pack (HCP) metals, slip of 〈c+a〉 dislocations on pyramidal planes is considered to be the most difficult slip mode that controls the overall plastic behavior. Nevertheless, pyramidal 〈c+a〉 slip is a requisite for accommodation of c-axis plastic deformation. In the present study, glissile pyramidal 〈c+a〉 dislocations with different characters gliding on type I pyramidal planes, informed by direct atomistic simulations, are reproduced and studied in HCP magnesium single crystals. The Peierls stresses for these dislocations are quantitatively evaluated via molecular dynamics simulations under pure shear loading. A high anisotropy in the Peierls stress is observed for different dislocation characters, with the near-screw having the lowest Peierls stress, and the near-edge dislocations having the highest stress. Local shuffling is also found to significantly reduce the Peierls stress of near-edge dislocations. These quantifications of pyramidal 〈c+a〉 slip provide better understanding of plastic deformation in HCP metals, and also provide necessary inputs for meso-scale dislocation models such as discrete dislocation dynamics simulations and crystal plasticity simulations.