Experimental investigation and CALPHAD modeling of phase equilibria of the Cu–Ag–Zr system

Abstract

The phase equilibria of the Cu–Ag–Zr system at 600 and 500 °C were determined by X-ray diffraction (XRD) and scanning electron microscope (SEM) with energy dispersive X-ray spectrometry (EDS) techniques. Invariant reactions involving the ternary Cu4AgZr phase were investigated by differential scanning calorimetry (DSC) techniques. Two as-cast alloys were prepared to study the alloys solidification behavior. The solubilities of Cu in the AgZr2 and AgZr phases and of Ag in the Cu5Zr, Cu51Zr14, Cu10Zr7 and CuZr2 phases were measured, and the ternary compound Cu4AgZr was found with compositions of Cu58.70-72.57Ag10.31-21.52Zr16.74-19.78 and Cu58.18-75.04Ag6.08-23.36Zr17.50-18.88 at 500 and 600 °C, respectively. Seven invariant reactions were determined. By using the CALPHAD (CALculation of PHAse Diagrams) method, thermodynamic assessment of the Cu–Ag–Zr system was carried out based on the available experimental data from the literature and the present work. Substitutional solution model was used to describe the solution phases and sublattice models were used to describe binary and ternary compounds. The ternary compound Cu4AgZr was describe as (Cu, Ag)5(Zr)1. A set of self-consistent thermodynamic parameters of the Cu–Ag–Zr system was obtained. The isothermal sections at 500, 600 and 750 °C and liquidus projection were calculated, and the reaction scheme was constructed. The solidification behaviors of as-cast alloys were simulated under Gulliver-Scheil non-equilibrium condition. The calculated phase equilibria and simulated solidification behaviors are in agreement with the experimental data.