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.