Thermodynamic modeling and solidified microstructure of Ag—Sn—Zr ternary system

Abstract

The phase equilibria of the Ag—Sn—Zr ternary system were investigated over the whole composition via thermodynamic modeling coupled with key experiments. Twenty-two equilibrated alloys were prepared to determine the isothermal sections of the Ag—Sn—Zr system at 500, 700 and 900 °C by means of X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), and eight as-cast alloys were prepared to study the solidification behavior of the alloys. The solubilities of Zr, Sn and Ag in binary compounds of the Ag—Sn, Ag—Zr and Sn—Zr systems were measured. No ternary compound was found. Based on the thermodynamic descriptions of three constitutive binary systems as well as the experimental phase equilibria data obtained from the present work, thermodynamic assessment of the Ag—Sn—Zr system was carried out by the CALPHAD (Calculation of phase diagrams) approach. A set of thermodynamic parameters of the Ag—Sn—Zr system were obtained. The calculated isothermal sections are in good agreement with most of the reliable experimental data. The liquidus projection and reaction scheme of the Ag—Sn—Zr system over the whole composition were also presented. The solidification behaviors of as-cast alloys were simulated under Gulliver—Scheil non-equilibrium condition. The simulated and experimental results are consistent with each other.