Experimental investigation and thermodynamic calculation of phase equilibria in the Sn-Au-Ni system

Abstract

The phase equilibria of the Sn-Au-Ni system, including six isothermal section diagrams in the Sn-rich portion at 200–600°C, as well as three vertical sections at Au:Ni=1:1, 50at.%Sn, and 40at.%Sn, were investigated by means of differential scanning calorimetry (DSC), x-ray diffraction, and metallography. The experimental results indicated that (1) there exists a ternary compound Sn4AuNi2 that is stable up to about 400°C, (2) there are larger solubilities of Au in the Ni3Sn2 phase in the Sn-Ni system and Ni in the SnAu phase in the Sn-Au system, and (3) there is the two-phase equilibrium between Sn2Ni3 and SnAu compounds below 400°C, rather than the continuous phase region from the Sn2Ni3 to the SnAu phases reported previously. Thermodynamic assessment of the Sn-Au-Ni system was also carried out by using the calculation of phase diagrams (CALPHAD) method, in which the Gibbs energies of the liquid, fcc, and hcp phases are described by the subregular solution model and that of compounds, including a ternary compound, are represented by the sublattice model. The thermodynamic parameters for describing each phase were optimized and good agreement between the calculated and experimental results was obtained.