Superdislocation dissociation in twist boundaries

In a recent paper low angle twist boundaries were observed in boron free and boron doped Ni-rich Ni sub 3 Al manufactured by hot pressing together Ni-24 at.% Al single crystals with {001} surfaces. As the misorientation angle increased so did the dissociation distance of the screw superpartials. This was deduced to reveal a change in APB energy and interpreted tentatively in terms of an increase in Ni-enrichment with increase of misorientation angle. It is shown here that the increase in dissociation distance is a natural consequence of APBs' cancelling out each other and that there is no reason to believe the APB energy is changing markedly as a function of boundary misorientation.