Two isothermal sections of the Co–Cu–Ti ternary system at 973 and 1123 K were experimentally determined using the diffusion triple technique together with scanning electron microscopy and electron probe microanalysis. The solubility of Cu (substituting Co) in CoTi increased from 22.8 at.% at 973 K to 28.1 at.% at 1123 K while that of Co (substituting Cu) in CuTi decreased from 11.1 to 8.8 at.% accordingly. In addition, the solubility limits of the third element in the binary compounds CoTi2, CuTi2, Cu4Ti3, and Cu3Ti2 were remarkable. Besides the solubility change, we found the Cu2Ti phase was stable at 1123 K but disappeared at 973 K. A ternary compound “m” with a composition range covering Co10Cu57Ti33 was detected at both isothermal sections. An invariant reaction Cu4Ti3 + CoTi ↔ CuTi + m at a temperature between 973 and 1023 K was deduced. Further investigations are necessary to confirm the reactions among Cu, Cu4Ti, Cu2Ti, Cu3Ti2, and “m” between 1023 and 1123 K.

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, AuSn 2 , and AuSn 4 . 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 380°C. The isothermal section at 396°C, the CoSn-Au and Au-SnCo vertical sections, and the liquidus projection were also calculated.

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