TIGHT-BINDING CALCULATIONS OF THE NI-AL PHASE-DIAGRAM

Tight-binding electronic band-structure calculations were combined with a free-energy expression given by the cluster-variation method. The effective pair interactions used in the cluster-variation method were evaluated by the cluster-Bethe-lattice method. They are restricted to the first-nearest neighbors in fcc-based structures and to first- and second-nearest neighbors in bcc-based structures; s and d orbitals have been used for Ni, while s and p orbitals were included for Al. The phase diagram has been constructed incorporating both fcc and bcc lattices and the occurring ordered compounds. The liquid part has been evaluated using the same Hamiltonian, chemical short-range order being calculated in an isotropic environment. The calculated diagram agrees reasonably well with the one determined experimentally.