Deformation due to migration of faceted 10(1)over-bar2 twin boundaries in magnesium and cobalt
A Ostapovets and J Bursik and R Groger, PHILOSOPHICAL MAGAZINE, 95, 4106-4117 (2015).
Recent experimental observations show that 10 (1) over bar2 twin boundaries in hexagonal close-packed (hcp) metals are frequently faceted. The objective of this paper is to investigate the influence of this faceting on the strain produced by twinning. We show that basal- prismatic (BP) facets are terminated by opposite disclinations and the migration of these facets along a straight 10 (1) over bar2 twin boundary produces ordinary twinning shear. On the other hand, joining conjugate twins gives rise to BP facets terminated on the parent twin boundaries by identical disclinations. In this case, the strain produced by the migration of BP facets is an average between the strains produced by the individual conjugate twins. These theoretical studies are complemented by two EBSD measurements on cobalt that is closely related to magnesium. The misorientation profiles measured across two conjugate twin boundaries yield a misfit of approx. 7 degrees consistent with the theoretical prediction that the corner of a twin embryo is terminated by two identical disclinations, each accommodating a misfit of 3.7 degrees.
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