PREDICTION OF A (11(2)OVER-BAR-2) HCP STACKING-FAULT USING A MODIFIEDGENERALIZED STACKING-FAULT CALCULATION

We present a new approach for calculating generalized stacking-fault e nergies, which allows for in-plane relaxation of atoms. When applied t o the (<11(2)over bar 2>) slip plane in hcp materials, our approach pr edicts that a stable stacking fault occurs, associated with a slip of 1/6(<11(23)over bar>) equivalent to 1/2(c + a). This is consistent wit h the edge dislocation with b = (c + a) breaking into two partial disl ocations, each with b = 1/2(c + a) observed in previous simulations of the dislocation cores. The resulting generalized stacking-fault energ y profile may be useful in understanding the competition between {<11( 2)over bar 2>}(<11(22)over bar>) twinning (observed in Zr and Ti) and the related slip mode, observed in Mg, Co and Zn.