A thermodynamic assessment of the Au-Cu system

A CALPHAD-like assessment of the Au-Cu system has been carried out using ex perimental data for the solid and liquid phases. An optimised thermodynamic description for the liquid, the disordered and ordered phases, based on th e fee Bravais lattice, has been obtained. For the solid phases the Borelius -Gorski-Bragg-Williams approximation is used together with excess terms con taining 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 sa tisfactorily reproduces the experimental phase diagram and the thermodynami c properties for the liquid and all solid phases. A second assessment of th e liquid and the disordered solid phase only was also made, disregarding th e ordering transformations. In this case the fit to all relevant experiment al data at high temperature is improved over the fits from the 1st assessme nt. It is clear from these assessments clear that the current CALPHAD solut ion models have problems for systems with significant short range order and some suggestions for a less empirical model are made.