CORE STRUCTURE OF 1/3(1120) SCREW DISLOCATIONS ON BASAL AND PRISMATIC PLANES IN HCP METALS - AN ATOMISTIC STUDY

Atomistic studies of stacking faults and dislocation cores in several h.c.p. metals have been carried out using recently constructed empirical many-body potentials. These potentials are fitted so as to reproduce the correct c/a ratios and allow us to study the effect of the deviation from close packing upon the dislocation properties. First, the possible metastable stacking faults on basal and prism planes have been investigated using the concept of gamma-surfaces. Metastable stacking faults may exist on both these types of plane. On basal planes the corresponding displacement vector is always the same, determined by the crystal symmetry. However, on prism planes it varies with the material. The atomistic calculations of the cores of screw dislocations with the 1/3<112BAR0> Burgers vector in Mg, Ti and Be indeed show dissociations on both basal and prism planes, in accordance with the findings of the studies of stacking faults. Using these results we then analyse the energy balance between dissociations on basal and prism planes and relate those, as well as other structural features of the cores, to the deformation properties of h.c.p. metals.