Recent experiments have revealed that the
twin boundaries in hexagonal materials are decorated by
basal–prismatic (BP) facets. The objective of this paper is to investigate the mechanism that leads to the formation of these BP interfaces using atomistic simulations and to carry out their stability analysis under an externally applied shear. We demonstrate that the stability of the BP interface is a consequence of large capillary forces that are caused by differences of the energies of a perfect
twin boundary and the BP interface. The latter is formed by the glide of twinning disconnections and therefore agrees with the theory of admissible interfacial defects. This observation implies that the glide of twinning disconnections is a primary mechanism of the twin boundary migration.
The paper presents a new type of twin-like objects observed in rolled pure magnesium. They have {1126} and {1122} habit planes and their misorientations to the matrix are close to 56˚ and 63˚ about 10 10 axis, respectively. The ad hoc performed theoretical analysis and atomic simulations allow to interpret the objects as {1012} {1012} double twins formed by the simultaneous action of two twinning shears with completely re-twinned volume of primary twin. The observed inclinations from the ideal misorientations for such double twins can be explained by the compliance of the strain invariant condition in the twin boundary. It seems plausible that, once the double twin is formed, its twin boundaries are hard to move by glide of twinning disconnections. If so, these twins represent obstacles for the motion of crystal dislocations increasing the hardness of the metal.
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