An electron microscopy study of dislocation structures in Mg single crystals compressed along [0 0 0 1] at room temperature

Mg single crystals were compressed along [0 0 0 1] at room temperature to various stress levels (40, 80, 120, 160 and 320 MPa) and the evolution of dislocation structure with stress increment was investigated by TEM. 〈c+a〉 slip is confirmed to be the dominant deformation mode; the predominance of edge dislocation debris lying along the implies that screw 〈c+a〉 dislocations are more mobile than their edge counterpart. The 〈c+a〉 edge dislocation may dissociate into 〈c〉 and 〈a〉 dislocations, and the latter can extend further on the basal plane and bound a basal-stacking fault. Numerous 〈c+a〉-type dislocation loops are generated during deformation and together with point defects and edge dipoles, contribute to the observed high work hardening rate. The smaller (<100 nm in diameter) dislocation loops are perfect 〈c+a〉 dislocation loops but the larger loops dissociate into two concentric 1/6-type partial dislocations enclosing a basal-stacking fault. Since the Burgers vector of these perfect and faulted loops is out of the loop plane, these loops are sessile, change size by climb, and act as obstacles to mobile dislocations.