Phenomenological phase diagram calculation of the NiAl system in the Ni-rich region

Abstract

The calculation of the phase diagram of the Ni-rich region in the NiAl alloy system is performed using the phenomenological Lennard-Jones potentials, which account for the concentration dependence of pair interactions through volume dependence. The configurational entropy of the system is evaluated within the tetrahedron approximation of the cluster variation method, and the thermal vibrational effect is included using the Debye-Grüneisen model. Each Lennard-Jones potential parameter is estimated from the available experimental data on cohesive energies, relative lattice stabilities and lattice parameters of pure metals, and heat of formation and lattice parameters of stoichiometric compounds. Each potential is fitted to the Morse potential function to introduce thermal vibration effects. The free energy function is obtained using the fitted Morse parameters and subsequently refitted to the Lennard-Jones type potential as a function of atomic distance and temperature. The phase diagram of the Ni-rich portion is calculated and compared with the experimental phase diagram. The calculation reproduces reasonable values for the free energy of formation and the lattice parameter.