Thermodynamic Assessment of the Au-Co-Sn Ternary System

Phase relationships in the Au-Co-Sn ternary system have been thermodynamically assessed by using the CALPHAD technique. The existing thermodynamic descriptions of the binary Au-Sn and Co-Sn systems were improved by incorporating the ab initio calculated enthalpies of formation of the intermetallic compounds including AuSn, CoSn, AuSn2, and AuSn4. For consistency, the Au-Co system was reassessed on the basis of the same pure element data as adopted for the Au-Sn and Co-Sn systems. With the combination of the three binary descriptions, the Au-Co-Sn ternary system was assessed by taking into account the ternary solubility in the binary compounds and the formation of a ternary compound. The obtained set of thermodynamic parameters can reproduce the measured phase equilibria at 380A degrees C. The isothermal section at 396A degrees C, the CoSn-Au and Au-SnCo vertical sections, and the liquidus projection were also calculated.