Phase equilibria and solidification sequences of the Cu–Cr–Ag–X (X = Y, Zr) alloys supported by key experiments and CALPHAD method

The phase equilibria of the Cu–Cr–Ag–Y and Cu–Cr–Ag–Zr systems at 600 and 700 °C with a fixed Y and Zr contents of 5.0 at.% were extrapolated by CALPHAD (CALculation of PHAse Diagrams) method based on the thermodynamic parameters for the constitutive binary and ternary systems. Twelve Cu–Cr–Ag–Y and six Cu–Cr–Ag–Zr alloys were designed in different phase regions of extrapolated isothermal sections. The phases, phase compositions and microstructures of alloys were experimentally investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). No quaternary phase was found. The solubilities of the solid solution phases and intermediate compounds were measured. The solidified sequences and microstructures of the Cu–Cr–Ag–X (X = Y, Zr) as-cast alloys were experimentally investigated as well as simulated by Scheil model. The calculated results are in agreement with the experimental data, which indicates the accuracy of thermodynamic databases of the Cu–Cr–Ag–X (X = Y, Zr) systems. The present work lays an important foundation for establishing the thermodynamic database of multicomponent Cu alloys.