Unusual F3 stacking fault in magnesium

Abstract

An unusual F3 basal stacking fault resulting from twin-dislocation interaction in magnesium is observed in molecular dynamics simulation. The F3 fault is produced in the twin lattice from the interaction between a migrating (101¯2) twin boundary and a partial dislocation of either a prismatic 〈c〉 edge, or a prismatic 〈c+a〉 mixed dislocation in the matrix. The condition is that the partial dislocation needs to have a negative sign and lie on a plane intersecting a compression site of the twin boundary. The F3 fault can also be generated when a positive basal 〈a〉 mixed dislocation in the twin lattice, with slip plane intersecting a compression site of the twin boundary, interacts with a basal-prismatic twinning disconnection. The F3 fault comprises two I1 faults that have the same character but are separated by two basal layers. It has one end connected to the twin boundary, and the other end bounded by a lattice defect with a Burgers vector identical to that of a 30° Shockley partial dislocation. The formation frequency of the F3 fault is higher at a lower shear stress (below ∼400 MPa) and/or a lower temperature (100 K and 200 K). The F3 fault can decompose into a glissile 30° Shockley and a T2 fault at a temperature above ∼400 K. The relationships between the F3 fault and other types of basal stacking faults such as I2, T2 or paired I1 faults that are separated by multiple basal layers are discussed.