Optimization of the core-shell structures and grain boundary to improve the coercivity of high Ce-content Nd-Ce-Fe-B magnets

The development of Rare-earth iron-boron sintered magnets (RE-Fe-B) based on high-abundance cerium (Ce) is crucial in terms of economic efficiency. In this work, a series of high Ce-content sintered magnets were prepared by incorporating Pr45FebalB (Pr45) into [(PrNd)0.5Ce0.5]29.5FebalB. The further microstructural analysis revealed that the addition of Pr45 alloy resulted in the formation of a thick and widely distributed Pr-rich shell around the Ce-rich grains. Adding Pr45 alloy also significantly suppressed the impurity phase and expanded the diffusion channels of the base magnets. Thus, the coercivity (Hcj) of the base magnets was remarkably enhanced from 5.65 kOe to 9.77 kOe ~ 16.39 kOe. Subsequently, the grain boundary diffusion of dysprosium hydride (DyHx) powders was carried out in the optimized base magnets. Results of microstructural analysis showed that the matrix phase grains formed a dual-shell structure comprising a Dy-rich shell in addition to the original Pr-rich shell, thereby enhancing the anisotropic field of the matrix phase grains. The increment in Hcj of the diffused magnets ranged from 3.03 kOe to 5.36 kOe (the original unoptimized diffusion magnet coercivity was only 1.69 kOe). This work provides a novel solution for preparing high-coercivity Nd-Ce-Fe-B sintered magnets.