First-principles local density functional calculations were used to investigate equilibrium point defect structures and B-defect interactions. It was noted that the predominant point defects in off-stoichiometric material were substitutional antisite defects on both sub-lattices. The B binding energy depended upon the lattice coordination. It was greatest near to vacancy sites with a nearest-neighbor Ni coordination number of about 4 (rather than 6 as in the defect-free interstitial site) and no Al atom nearest-neighbors. This suggested that B tended to segregate to so-called open defect sites and to enhance cohesion via the formation of localized Ni-B covalent bonds. A comparison of the binding energies of B and C showed that B exhibited a greater tendency to segregate to the open sites than did C.

Point Defects and the Binding Energies of Boron near Defect Sites in Ni3Al: a First-Principles Investigation. Fu, C.L., Painter, C.S.: Acta Materialia, 1997, 45[2], 481-8