Calculated site substitution in ternary γ|IH - Ni3 Al: Temperature and composition effects

The temperature and composition dependence of the site substitution behavior of ternary additions to ${\mathrm{Ni}}_{3}$Al is examined on the basis of first-principles calculations of the total energies of ternary, partially ordered (${\ensuremath{\gamma}}^{|\mathrm{I}\mathrm{H}}$) alloys. The calculations are performed by means of the linear muffin-tin orbitals method in conjunction with the local-density and multisublattice coherent-potential approximations and include all 3d, 4d, 5d, and noble metals. The calculations show the existence of simple trends in the alloying behavior of the ${\ensuremath{\gamma}}^{|\mathrm{I}\mathrm{H}}$ phase which may be explained in a Friedel-like model based on the interaction between Ni and the added species. It is shown that the commonly accepted interpretation of the site substitution behavior of Cu and Pd may be incorrect because of site substitution reversal at high temperatures. It is further shown that the direction of the solubility lobe in the ternary phase diagram for the elements Co, Pd, Cu, and Ag incorrectly has been interpreted as evidence for strong Ni site preference and that, in fact, these elements are expected to exhibit only weak Ni site preference.