Site substitution of ternary additions to Ni3Al ( gamma ') from electronic-structure calculations.

Abstract

A real-space, Green-function method is proposed to examine the electronic structure and site preference of substitutional ternary additions to ${\mathrm{Ni}}_{3}$Al (\ensuremath{\gamma}') using the tight-binding method of linear muffin-tin orbitals (TB-LMTO). Pairs of atoms are embedded in a random ${\mathrm{Ni}}_{0.75}$${\mathrm{Al}}_{0.25}$ medium (of approximately 1000 atoms), one-electron energies are obtained by performing recursion on the TB-LMTO Hamiltonian, and the effective pair interactions (EPI's) determined by configurational averaging. Depending on the relative values of the three EPI's, ${\mathit{W}}_{\mathrm{Ni}\mathrm{\ensuremath{-}}\mathrm{Al}}$, ${\mathit{W}}_{\mathrm{Ni}\mathrm{\ensuremath{-}}}$X, and ${\mathit{W}}_{\mathrm{Al}\mathrm{\ensuremath{-}}}$X, the ternary addition may occupy either the Ni site or the Al site exclusively, or the site preference may be a function of alloy stoichiometry. The site-substitution behavior in both stoichiometric and nonstoichiometric ${\mathrm{Ni}}_{3}$Al alloys is computed for six ternary additions, X (X=Co,Cu,Zn,Rh,Pd,Si). The theoretical predictions are in excellent agreement with experimental data, where available.