The core structures of <c+a> dislocations in hexagonal close-packed metals were investigated by using molecular dynamics simulations and a Lennard-Jones type of pair potential. The <c+a> edge dislocation had 2 types of core at 0K. One was a perfect dislocation (type-A), and the other had two ½<c+a> partials (type-B). The type-A transformed to type-B upon abruptly increasing the temperature from 0 to 293K, while type-B was stable at 0 to 293K. Type-A extended parallel to (00•1) at 30K, and this extended core was still stable at 293K. The results suggested that the <c+a> edge dislocation glided, on {11•2}, as two ½<c+a> partial dislocations and became sessile due to changes in the core structure. The <c+a> screw dislocation was 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} while 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 upon the shear direction could be explained in terms of the core structures.

Molecular Dynamics Simulation of <c+a> Dislocation Core Structure in Hexagonal Close-Packed Metals. S.Ando, T.Gotoh, H.Tonda: Metallurgical

Transactions A, 2002, 32[3A], 823-9