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

A real-space, Green-function method is proposed to examine the electronic structure and site preference of substitutional ternary additions to Ni3Al () using the tight-binding method of linear muffin-tin orbitals (TB-LMTO). Pairs of atoms are embedded in a random Ni0.75Al0.25 medium (of approximately 1000 atoms), one-electron energies are obtained by performing recursion on the TB-LMTO Hamiltonian, and the effective pair interactions (EPIs) determined by configurational averaging. Depending on the relative values of the three EPIs, WNi-Al, WNi-X, and WAl-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 Ni3Al 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.