Why are [formula omitted] twins profuse in magnesium?

Abstract

We show that {101¯2} twinning in magnesium acts as an effective sink of basal dislocations without loss of mobility. The lattice dislocation decomposes into the b0/0BP dislocation recently identified by the present authors, and a residual dislocation. The b0/0BP dislocation in turn spontaneously decomposes into a Burgers vector content of the basal-prismatic facet related disclination dipole, f0BP, plus an associated number of twinning disconnections. The residual dislocation lies on the basal-prismatic facet and thus remains glissile should the twin boundary move forward or recede back. Importantly, the basal-prismatic facet absorbs any twinning disconnection gliding on one side of the twin boundary and releases another one to other side, thereby enabling the twin boundary to progress through a forest of basal dislocations with no apparent decrease in mobility or loss of coherency. This mechanism explains why {101¯2} twinning is profuse in hexagonal close-packed metals as slip induces the interfacial atomic structure to change favorably for twin propagation.