Phase Equilibria and Magnetic Phases in the Ce-Fe-Co-B System

Ce-Fe-Co-B is a promising system for permanent magnets. A high-throughput screening method combining diffusion couples, key alloys, Scanning Electron Microscope/Wavelength Dispersive X-ray Spectroscope (SEM/WDS), and Magnetic Force Microscope (MFM) is used in this research to understand the phase equilibria and to explore promising magnetic phases in this system. Three magnetic phases were detected and their homogeneity ranges were determined at 900 °C, which were presented by the formulae: Ce₂Fe_14-xCo_xB (0 ≤ x ≤ 4.76), CeCo_4-xFe_xB (0 ≤ x ≤ 3.18), and Ce₃Co_11-x Fe_xB₄ (0 ≤ x ≤ 6.66). The phase relations among the magnetic phases in this system have been studied. Ce₂(Fe, Co)₁₄B appears to have stronger magnetization than Ce(Co, Fe)₄B and Ce₃(Co, Fe)₁₁B₄ from MFM analysis when comparing the magnetic interactions of selected key alloys. Also, a non-magnetic CeCo_12-xFe_xB₆ (0 ≤ x ≤ 8.74) phase was detected in this system. A boron-rich solid solution with Ce₁₃Fe_xCo_yB₄₅ (32 ≤ x ≤ 39, 3 ≤ y ≤ 10) chemical composition was also observed. However, the crystal structure of this phase could not be found in the literature. Moreover, ternary solid solutions ε₁ (Ce₂Fe_17-xCo_x (0 ≤ x ≤ 12.35)) and ε₂ (Ce₂Co_17-xFe_x (0 ≤ x ≤ 3.57)) were found to form between Ce₂Fe₁₇ and Ce₂Co₁₇ in the Ce-Fe-Co ternary system at 900 °C.