Computer simulation of dislocation cores in h.c.p. metals II. Core structure in unstressed crystals

Abstract

The four pair-wise potentials found in part I (Bacon and Liang 1986) to define model hexagonal-close-packed crystals in equilibrium have been used for the computer simulation of dislocation cores in the absence of external stress. Straight dislocations with Burgers vector b equal to either ⅓〈1120〉 or 1/3〈1123〉 have been considered. For the former, the screw and the edge lying along 〈1200〉 dissociate on the basal plane to a width expected from the stacking-fault energy found in part I, but not always to two Shockley partials. The screw in one crystal has a more stable core when the disregistry spreads on the {1100} prism plane. The stable core of the edge lying along 〈0001〉 is not dissociated in any of the models, and contains a microcrack in one case. The ⅓〈1123〉 edge dislocation lying along 〈1100〉 has two stable core states in all the crystals. One consists of combinations of {1121} and {1122} microtwins and microcracks, the precise form depending on the potential, and in the other the 〈1123〉 disregistry is extended on the {1122} plane. The 〈1123〉 screw also has a variety of stable forms in every crystal, the disregistry being concentrated on combinations of {102 2}, {112 2} and {1100} planes. All the cores modelled are discussed in terms of the γ-surfaces determined in part I.