A study was made of the atomic structure of [001] symmetrical tilt grain boundaries with stoichiometric composition by using molecular statics and an embedded-atom potential. The simulations were performed for misorientations ranging from 0 to 90˚, in average steps of 3˚. The multiplicity of stable grain boundary structures was addressed by using the γ-surface technique, combined with full atomic relaxation. The grain boundaries typically exhibited only a few non-identical stable structures. All of the other structures were either symmetrically related to those few structures, or were their strained variants and reduced to one of them if relative translations of the grains were allowed. All of the ground-state structures were composed of only 4 types of structural unit, or their variants as obtained by site substitution. It was noted that many structural features of the grain boundaries could be understood in terms of the significant atomic size effect which was peculiar to NiAl. The ground-state Σ = 5 (310) θ = 36.87˚ and Σ = 5 (210) θ = 53.13˚ grain boundaries, as well as all of those with intermediate orientations, exhibited a relative shift of the grains by ½[001]. All such grain boundaries followed the structural unit model, with the two Σ = 5 grain boundaries being the delimiting boundaries. For all other orientations, the ground-state grain boundary structures had no shift along the tilt axis and were consistent with the structural unit model only at θ < 30˚ and θ > 65˚. In some grain boundaries, the primary or secondary grain boundary dislocations were seen to dissociate into partials which were associated with grain boundary steps. Many grain boundaries contained regions of antiphase boundary on (100) and (110) planes.

Atomistic Simulation of [001] Symmetrical Tilt Grain Boundaries in NiAl Y.Mishin, D.Farkas: Philosophical Magazine A, 1998, 78[1], 29-56