A thermodynamic assessment of the Au-Cu system

A CALPHAD-like assessment of the Au-Cu system has been carried out using experimental data for the solid and liquid phases. An optimised thermodynamic description for the liquid, the disordered and ordered phases, based on the fee Bravais lattice, has been obtained. For the solid phases the Borelius-Gorski-Bragg-Williams approximation is used together with excess terms containing adjustable parameters in order to compensate for the poor treatment of the configurational contribution to the entropy. The model is developed in the framework of the Compound Energy Formalism (CEF). The assessment satisfactorily reproduces the experimental phase diagram and the thermodynamic properties for the liquid and all solid phases. A second assessment of the liquid and the disordered solid phase only was also made, disregarding the ordering transformations. In this case the fit to all relevant experimental data at high temperature is improved over the fits from the 1st assessment. It is clear from these assessments clear that the current CALPHAD solution models have problems for systems with significant short range order and some suggestions for a less empirical model are made.