First Principles Calculation of Phase Diagrams

Abstract

Phenomenological theories of phase equilibrium have been successfully used to characterize the main contributions to alloy phase stability, the interpretation of complex and extensive experimental data and, in some instances, the prediction of metastable phases. At present, there is increased interest in elucidating the extent to which microscopic quantum theory can be combined with statistical mechanics to produce a reliable description of phase equilibrium and, in particular, phase diagrams. This question will be explored using a first-principles statistical mechanics theory which incorporates the calculation of electronic total energies in the local density approximation, configurational entropies, vibrational modes and local volume relaxations in disordered systems. Applications of the theory to the binary Ni-Al and ternary Ni-A1-Ti systems are given using the Linear Muffin-Tin Orbital method for the total energy calculations, the Cluster Variation method for the description of the configurational entropy, and the Debye-Grüneisen approximation for the vibrational modes.