Thermodynamic assessment of Co-Cr-W ternary system

The Co-Cr-W ternary system was critically assessed using the CALPHAD technique. The solution phases including the liquid, γ-Co, ɛ-Co and α-Cr were described by a substitutional solution model. The σ, μ and R phases were described by three-sublattice models of (Co, W)8(Cr, W)4(Co, Cr, W)18, (Co, Cr, W)7W2(Co, Cr, W)4 and (Co, W)27(Cr, W)14(Co, Cr, W)12, respectively, in order to reproduce their homogeneity ranges. A self-consistent set of thermodynamic parameters for each phase was derived. The calculated isothermal sections at 1 000, 1 200 and 1 350 °C are in good agreement with the experimental data. A eutectoid reaction of R ⇔ μ+γ-Co+σ in this ternary system was predicted to occur at 1 022 °C.