Thermodynamic assessment of the Co–Cu–Fe system and diffusion study of its fcc phase

The Co–Cu–Fe ternary system was thermodynamically reassessed with the CALPHAD method in the present work. The miscibility gap of the fcc phase at 1373 K was experimentally determined. The phase relationship among the liquid, Cu-rich and Cu-depleted fcc phases was established. Based on the new experiment data and available data in the literature, the thermodynamic optimization of the Co–Cu–Fe system was carried out. The experimental phase equilibria over the whole composition range can be reproduced. Additionally, in order to optimize the temperature-dependent mobility parameters, the interdiffusion coefficients at 1373 K and 1473 K were measured with the diffusion-couple method. Based on the updated thermodynamic description and atomic mobilities in the binary subsystems, the atomic mobilities of Co, Cu and Fe in the fcc phase were re-optimized. The measured composition profiles and diffusion paths of diffusion couples can be well reproduced using the present mobility parameters.