Phase Equilibria and Solidification Behavior of Sm–Co–Cu Ternary System via Experimental Investigation and Thermodynamic Calculation
摘要
Phase equilibria and solidification behavior of the Sm–Co–Cu ternary system were studied by using scanning electron microscope with energy dispersive spectroscopy (SEM–EDS) and X-ray diffraction (XRD). The results of phase equilibria reveal that ten binary intermetallic compounds including SmCo2, SmCo3, Sm2Co7, Sm5Co19, SmCo5, Sm2Co17, SmCu2, SmCu4, SmCu5, and SmCu6 were observed, and the ternary intermetallic compounds were not detected. The continuous solid solution phase Sm(Co, Cu)5 is formed from the respective SmCo5 and SmCu5. The solubility of Cu in SmCo2, SmCo3, Sm2Co7, and Sm2Co17 and that of Co in SmCu2 and SmCu4 were determined. Three isothermal sections at 873 K, 1073 K, and 1273 K were established. Meanwhile, solidification microstructures of Sm10.5Co89.5−xCux as-cast alloys were examined. Furthermore, on the basis of the present and earlier experimental results, thermodynamic calculation of the Sm–Co–Cu ternary system was carried out using the CALPHAD method. The calculated isothermal sections and vertical sections in this ternary system are in good agreement with the experimental results. Finally, solidification processes of several Sm–Co–Cu as-cast alloys were simulated using the Scheil–Gulliver module with thermodynamic parameters. The simulated results are satisfactorily consistent with the experimental solidification microstructure. It indicates that thermodynamic parameters of this ternary system obtained in this work are self-consistent and reasonable. The present parameters would provide the proper foundation to develop a thermodynamic database of multi-component Sm–Co-based magnetic alloys, which is valuable information for exploring high-performance and low-cost Sm–Co–Cu-based permanent magnets.