Twins as barriers to basal slip in hexagonal-close-packed metals

The boundary structure of {10 (1) over bar1}, {10 (1) over bar2}, {11 (2) over bar1}, and {11 (2) over bar2} twins in hexagonal-close-packed (hcp) metals and the interaction of crystal dislocations with the first two twin types have been studied previously using atomic-scale computer simulation. The interaction of crystal dislocations with {11 (2) over bar1} and {11 (2) over bar2} twin boundaries is described here and compared with the results for {10 (1) over bar1} and {10 (1) over bar2} twins. These four twins are found to create barriers to the motion of crystal dislocations gliding on the basal plane, and the strength of the barrier depends in a relatively complex manner on crystallographic parameters and details of the atomic structures of the interfaces. In some circumstances, crystal dislocations can be transmitted through the twin boundary, thereby creating twinning dislocations.