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: Ce₂Fe14-xCoxB (0 ≤ x ≤ 4.76), CeCo4-xFexB (0 ≤ x ≤ 3.18), and Ce₃Co11-x FexB₄ (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 CeCo12-xFexB₆ (0 ≤ x ≤ 8.74) phase was detected in this system. A boron-rich solid solution with Ce13FexCoyB45 (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 (Ce₂Fe17-xCox (0 ≤ x ≤ 12.35)) and ε₂ (Ce₂Co17-xFex (0 ≤ x ≤ 3.57)) were found to form between Ce₂Fe17 and Ce₂Co17 in the Ce-Fe-Co ternary system at 900 °C.