Abstract

Twinning plays an important role in materials with low symmetry, e.g. hcp metals (Mg, Ti and their alloys). Migration of twin boundaries are often accompanied by deformation of material (deformation and transformation twins). Classical twin boundaries are considered as flat interfaces lying along a plane, which is invariant to twinning shear. However, in general, twin is a 3-dimensional object, which can be bounded by different types of interfaces. Some of these interfaces are significantly different from symmetrical invariant interfaces. Present work discusses unusual twin interfaces in hcp metals. The examples of such interfaces are less common twins (e.g. (1 1 -2 6) twin) and asymmetrical twin boundaries, which are widely observed during previous years. Connection between twin boundary migration mechanisms and nucleation of asymmetrical facets in twin boundaries is considered.