The core structures of <c+a> dislocations in hexagonal-close-packed metals were investigated by molecular dynamics simulations using a Lennard-Jones-type pair potential. The <c+a> edge dislocation has 2 types of core at 0K; one was a perfect dislocation (type-A), and the other had two ½<c+a> partials (type-B). Type-A transformed to type-B upon abruptly increasing the temperature from 0 to 293K, while type-B was stable at 0 to 293K. In contrast, type-A extended parallel to (00▪1) at 30K, and this extended core was still stable at 293K. These results suggested that the <c+a> edge dislocation glided on the {11▪2} as two ½<c+a> partial dislocations and became sessile due to changes in the core structure. The <c+a> screw dislocation spread over two {10▪1} planes at 0K. The core transformed into an asymmetrical structure at 293K, which was spread over {11▪2} and {10▪1} and core spreading occurred parallel to {11▪2} at 1000K. The critical strain required to move screw dislocations depended upon the sense of the shear strain. The dependence of the yield stress on the shear direction could be explained in terms of these core structures.

Molecular Dynamics Simulation of <c+a> Dislocation Core Structure in Hexagonal-Close-Packed Metals. S.Ando, T.Gotoh, H.Tonda: Metallurgical and Materials Transactions A, 2002, 33[3A], 823-9