Phase Equilibria, Thermodynamics and Solidified Microstructure in the Copper-Zirconium-Yttrium System

A copper alloy with the addition of zirconium and yttrium is an attractive high strength and high conductivity (HSHC) copper alloy. The study of the solidified microstructure, thermodynamics and phase equilibria in the ternary Cu-Zr-Y system is expected to provide new insight into designing an HSHC copper alloy. In this work, the solidified and equilibrium microstructure and phase transition temperatures in the Cu-Zr-Y ternary system were studied by X-ray diffraction (XRD), electron probe microanalysis (EPMA) and differential scanning calorimeter (DSC). The isothermal section at 973 K was experimentally constructed. No ternary compound was found, while the Cu₆Y, Cu₄Y, Cu₇Y₂, Cu₅Zr, Cu₅₁Zr₁₄ and CuZr phases substantially extended into the ternary system. According to the experimental phase diagram data from the present work and the literature, the Cu-Zr-Y ternary system was assessed using the CALPHAD (CALculation of PHAse diagrams) method. The isothermal sections, vertical section and liquidus projection calculated by the present thermodynamic description agree well with the experimental results. This study not only establishes a thermodynamic description of the Cu-Zr-Y system, but also contributes to the design of a copper alloy with the required microstructure.