Dependence of the antiphase boundary energy upon orientation in the L1₂ structure

Abstract

Antiphase boundaries are examined in an L1₂ structure, with particular attention paid to those that result from dissociation via a glide or a climb process of a superlattice dislocation with an a〈110〉 Burgers vector. In the case of a climb dissociation process, emphasis is placed on those antiphase boundaries which could exhibit local deviations from the stoichiometric composition A₃B.

The antiphase boundary energies are computed for a number of plane orientations so as to leave no region of the stereographic projection unexplored. A set of empirical potentials representing mechanically stable L1₂ alloys with different glide antiphase boundary energies on {001} and {111} and two distinct anisotropy ratios are used. It is found that the main effect of atomic relaxation is to significantly reduce the amplitude of the antiphase boundary energy variations with orientation: given the a/2[110] displacement vector, the low antiphase boundary energy on (001) is practically unaffected, whereas the high antiphase boundary energies in the region containing (100) and (110) are considerably reduced. The implications of these results on dislocation dissociation are found to be in general agreement with the available configurations reported so far from weak-beam experiments on Ni₃Al.