Experimental investigation and thermodynamic calculation of the Co–Zn–Zr ternary system

The phase equilibria of the Co–Zn–Zr ternary system were systematically studied by combining experimental analysis and thermodynamic modelling. The 450 °C isothermal section at the Zn-rich corner and the 600 °C isothermal section of Co–Zn–Zr system were studied by means of scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Seventeen and ten three-phase regions were obtained at 600 and 450 °C isothermal sections, respectively. Three stable ternary compounds named τ₁ (ZrCo₂Zn₂₀), τ₂ (Zr₅Co₃Zn₁₂) and τ₃ (Zr₁₀Co₃Zn₇) were found in the 600 °C isothermal section. Among them, the Bravais lattice symmetry of the τ₂ phase is a simple tetragonal lattice, and its lattice parameters are a = 8.945 Å, b = 8.945 Å, c = 11.737 Å and α = β = γ = 90°. Based on the comprehensive evaluation of the current experimental results and the data reported in the literature, the thermodynamic description of the system was developed using the CALPHAD technique. A set of self-consistent thermodynamic parameters for the Co–Zn–Zr ternary system was obtained with good agreement between the experimental and calculated results.