Effect of grain boundary dislocations on 9R stacking errors at an incoherent twin boundary in copper

We consider the nature of faults in the dissociated 9R phase at an incoherent twin boundary in copper, analysis of the dislocation content of a five-layer break in the normal ABC/BCA/CAB stacking sequence of the 9R shows that this defect is associated with a secondary grain boundary dislocation (SGBD) of Burgers vector a/6[(2) over bar 11]. Atomistic simulations of SGBDs at the incoherent twin interface show that the sign of the Burgers vector is important to determining the core structure of the dislocation. The resulting atomistic structures and the five-layer width of the fault can be directly understood by analyzing the set of twinning dislocations that make up the boundary. Atomistic calculations show further, in agreement with the experimental observations, that a shear parallel to the interface causes an increase in the fault width that accompanies the growth of the 9R phase.