Twinning dislocations on {1¯011} and {1¯013} planes in hexagonal close-packed crystals

Abstract The objective of this investigation was to identify the elementary twinning dislocations (TDs) for { 1 ¯ 0 1 1 } and { 1 ¯ 0 1 3 } twins by fully characterizing their structure for an Mg crystal. For both { 1 ¯ 0 1 1 } and { 1 ¯ 0 1 3 } twins, we conclude that the 2-layer TD, not the 4-layer TD, is the active TD in twinning. The 4-layer TD can be considered as the combination of two 2-layer TDs with opposite-sign screw components. Molecular statics simulations of the Peierls energy show why the TDs of both twinning modes (for c/a ratios > 1.5) are only activated when the c-axis experiences a compressive strain. The simulations predict that 2-layer TDs are more mobile than 4-layer TDs and that the mobility of these twinning dislocations depends strongly on dislocation character. Correspondingly, the influence of TDs involved in deformation twinning processes on deformation twins is discussed.