Dislocations in interfaces in the hcp metals - I. Defects formed by absorption of crystal dislocations

Atomic-scale computer simulation techniques have been used to investigate t he interaction of crystal dislocations with two interfaces in hexagonal-clo se-packed (h.c.p.) metals, namely the {10 (1) over bar 2} twin boundary and a (1 (2) over bar 10]/90 degrees tilt boundary which is incommensurate in the direction perpendicular to the lilt axis. Crystal dislocations are alwa ys found to be absorbed in the tilt boundary with concomitant reconstructio n of their cores. In the twin boundary, a broader range of interactions is observed, including defect transmission from matrix to twin and decompositi on in the interface into discrete defects. The easy generation of mobile tw inning dislocations facilitates the latter behaviour. The simulations demon strate that the core structures of localized interfacial defects exhibit pr eferred riser configurations. For the twin, the favoured structure is the " basal-on-prism" configuration, whereas risers in the tilt boundary resemble {10 (1) over bar 2} twin forms. By comparing interaction processes in two interfaces, this investigation elucidates the role of crystallographic cons iderations and interfacial structure. It also illustrates that the core str ucture of interfacial defects can be complex and contributes significantly to total defect energy. (C) 1999 Acta Metallurgica Inc. Published by Elsevi er, Science Ltd. All rights reserved.