Interaction of twin boundaries with stacking faults in 2H martensite: A high-resolution electron microscopy study

Twinned 2H martensite is observed in copper-based shape memory alloys together with basal and non-basal plane stacking faults. Knowledge of the twin-boundary structure and its interaction with the faults is important to understand the deformation mechanism by twin coalescence. High-resolution electron microscopy coupled with image simulations have been used for these studies. The interface of the type I twinning in 2H martensite shows an atomic configuration with mirror antisymmetry. An atomic plane is shared by the twinned variants in such a way that the distance between the planes, parallel to the interface, is unchanged at the boundary and the mean atomic volume is conserved. The interaction of the boundary with a basal plane fault generates a shift in the interface. A mirror antisymmetrical boundary is maintained by introducing an imperfect interface dislocation.