ИСТИНА

Noble metal alloys also containing copper and indium are widely used in dentistry, jewelry and other fields. Real alloys are multicomponent and experimental study of phase equilibria in them is difficult. One of most effective solutions of this problem is CALPHAD calculations based on thermodynamic analyses of binary and ternary subsystems. Phase equilibria of the Au–Cu–In system were investigated by a combination of key experiments and thermodynamic modeling. Partial isothermal section at 500°C of the Au-Cu–In system for In content less than 40 at.% have been plotted using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). No ternary compounds were found. The solubility of the third elements in the phases of the binary systems was measured. In addition, the temperatures of solidus and liquidus of α, gamma and η’ phases were measured by DTA/DSC. The calculation of phase equilibria was carried out using the Thermo-Calc® software. The properties of ternary phases were obtained by Muggianu extrapolation of the descriptions of binary phases with assessing the ternary interactions. Thermodynamic properties of disordered fcc, liquid and  phases were described by phenomenological models, and gamma, α, and η’ phases with the sublattice models. Thermodynamic descriptions of the Au–Cu, Au–In and Cu–In systems were accepted correspondingly from the literature data. However, the parameters of the fcc phase in Au–In edge had to be revised to take into account the new stability parameter of fcc indium from PURE5. In addition, the models for the gamma phase in Au–In and Cu–In systems had to be unified. We have chosen for both a model of gamma phase from Cu–In, basing on our results of an experimental study of the region of existence of this phase in the ternary. Then, the thermodynamic assessment of the Au–Cu–In ternary system was carried out using the CALPHAD approach. We could achieve a good agreement for both calculated phase equilibria at 500°C and solidification curves with our experimental data.