The atomic structure of dislocations in h.c.p. metals I. Potentials and unstressed crystals

Abstract

The c/a ratio, vacancy-formation energy, elastic constants and phonon frequencies for metals having the h.c.p. structure are assessed and it is found that, although empirical potentials for individual metals have not as yet been developed, data for most metals are fitted reasonably well by a truncated Lennard—Jones potential. It is shown that two truncations simulate stable structures with high and low stacking-fault energies. They have been used in computer modelling of the core structure of prism-edge, basal-edge and screw dislocations having b = 1/3⟨11·20⟩. The prism-edge dislocation has a wider core than given by elasticity theory, hut simple dissociations predicted previously are not observed. In contrast, the expected basal dissociations do not occur: the width of the stacking-fault ribbon is less than that given by elasticity theory and the partial cores are wider. Contrary to results of an earlier study which used a copper potential however, the stacking-fault energy obtained by elasticity theory from the spacing of the partials is close to the true value. The core of the screw dislocation is distributed solely along the basal plane.