Thermodynamic evaluation of the Au-Sn system

The Calphad method has been employed in order to generate a simple and robust thermodynamic description of the Au-Sn system. Inconsistencies in a previous thermodynamic assessment of this system are pointed out. The reassessment is based on the published original experimental data on phase equilibria and thermodynamic alloy properties, which have been critically evaluated. The particular behaviour of the mixing enthalpy of the liquid phase and the claimed short-range order are addressed. The substitutional solution model has been employed for the solution phases alpha-(Au), beta-(Au10Sn) and epsilon-(AU(5)Sn), while the intermediate phases zeta'-AU(5)Sn, delta-AuSn, epsilon-AuSn2 and eta-AuSn4 are considered as stoichiometric phases. The assignment of reasonable values of thermodynamic parameters is further demonstrated by the consideration of absolute entropies and entropies of fusion of all the intermetallic compounds.