Abstract :
Different models used to describe the thermodynamics of order-disorder transitions are investigated and applied to the assessment of the Ni-Al system. The models in question use different modifications of the Calphad methodology and also combine the Calphad approach with the Cluster Variation Method. For the Ni-Al system, it is shown that excellent and comparable results can be achieved by adding small Calphad-type corrections to the alloy free energy in a phenomenological Cluster Variation approach. The corrections, necessary for an accurate description of the phase diagrams, are identified with contributions due to harmonic and anharmonic vibrational modes and to electronic excitations.
