Thermodynamic Assessment of Co-Nb-W System

Abstract The thermodynamic assessment of the Co-Nb-W ternary system has been carried out by applying the CALPHAD method. A slight modification of the Co-W binary system has been performed to unify the model of μ phase in Co-Nb-W system. The three published isothermal sections at 1273, 1373 and 1473 K have been critically examined and used to optimize the model parameters. The solution phases, including α Co and bcc were modeled as substitutional solutions; the λ, χ , and Co 3 Nb phases have been assessed using two-sublattice models. The Co 7 W 6 and Co 7 Nb 6 phases were described as (Co, Nb) 1 (Co, Nb, W) 2 (Co, Nb, W) 4 (Co) 6 . Calculated isothermal sections and vertical sections agreed well with the experimental data.