The Impact of Ho Addition on the Microstructural Features and Magnetic Performances of Sintered NdFeB Magnets

Two NdFeB magnets with distinct compositions were fabricated via an identical process. One magnet was doped with 2.5 wt.% of Ho, whereas the other remained undoped. Subsequently, grain boundary diffusion was performed on both magnets using metallic Tb, adopting the same set of technological parameters. A comprehensive analysis was conducted on the magnetic properties, phase compositions, microstructures, and elemental distributions of these two magnets. The findings indicate that the incorporation of Ho enhances the utilization efficiency of Tb. As a result, the magnets can achieve higher coercivity across different temperatures, with only a minor reduction in remanence. During the sintering process of the Ho-doped magnet, fine precipitated particles of Ho2Fe14B are generated inside the magnet. This phenomenon causes the refinement of the main grains of the magnet. The refined main grains facilitate the effective diffusion of Tb within the magnet, eliminating the formation of the anti-shell structure. Furthermore, when Ho substitutes for Nd, it leads to a more homogeneous distribution of the Nd-rich phase. Additionally, it increases the densification degree of the sintered NdFeB magnets. These effects contribute to a further enhancement of the magnets’ coercivity.