Analysis of the influence mechanism of CeFe2 phase on coercivity in high-performance Nd-Ce-Fe-B diffusion magnets

Abstract

In this study, we have prepared high-performance (Nd, Ce)-Fe-B magnets with 16.95 wt% and 23.73 wt% Ce / total rare earth (TRE) content, as well as Dy diffusion magnets. The concern between the CeFe₂ phase, microstructure, and coercivity of the magnets was clarified. When the Ce / TRE content increased to 23.73 wt%, a little of the CeFe₂ phase appeared in the magnet, which improved the fluidity of the liquid phase, promoted the formation of grain boundary phases (GBs), and optimized the microstructure. Therefore, when the GBs thickness increased to 6.39 nm, the coercivity slightly increased. However, in the subsequent heavy rare earth grain boundary diffusion, the coercivity increment (ΔH_cj) of the magnet with the CeFe₂ phase was 2.96 kOe, lower than the 4.68 kOe in the magnet without the CeFe₂ phase. From theoretical calculations and experimental results, the diffusion channel of the Dy elements was blocked by the CeFe₂ phase, and the Dy atom would enter the CeFe₂ phase to form the (Ce, Dy)Fe₂ phase. Therefore, the presence of the CeFe₂ phase led to a smaller diffusion depth of Dy elements, less core–shell structure of the main phase, lower effective Dy utilization rate, and lower ΔH_cj.