WORKSHOP ON THERMODYNAMIC MODELING, OF SOLUTIONS AND ALLOYS - SCHLOSS-RINGBERG, MARCH 10-16, 1996 - GROUP 3 - ORDER-DISORDER PHASE-DIAGRAMS

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 C alphad methodology and also combine the Calphad approach with the Clus ter Variation Method. For the Ni-Al system, it is shown that excellent and comparable results can be achieved by adding small Calphad-type c orrections to the alloy free energy in a phenomenological Cluster Vari ation approach. The corrections, necessary for an accurate description of the phase diagrams, are identified with contributions due to harmo nic and anharmonic vibrational modes and to electronic excitations.