Effect of boron content on magnetic properties and microstructure of Dy-diffused sintered (Nd, Ce)-Fe-B magnets

Abstract

This study systematically investigates the effect of Boron (B) content on the magnetic properties and microstructure of Dy-diffused sintered (Nd, Ce)-Fe-B magnets, aiming to optimize the overall performance of low-cost Ce-containing magnets. Using conventional powder metallurgy, magnets with varying B contents (0.88–1.02 wt%) were fabricated, and DyH₃ was used as a diffusion source for grain boundary diffusion (GBD) treatment. The mechanisms by which B content influences magnetic performance, grain boundary phase distribution, and Dy diffusion efficiency were analyzed. The results show that increasing B content reduces the coercivity (H_cj) of the initial magnets from 13.88 kOe (0.90 wt% B) to 12.16 kOe (1.02 wt% B), while significantly improving remanence (B_r) and maximum energy product ((BH)_max). The magnets with low B content (0.90 wt% B) exhibit high H_cj due to the suppression of the magnetic coupling effect between the ferromagnetic initial grains by continuous grain boundary phases. After GBD treatment, the 0.95 wt% B magnets show the greatest increase in H_cj (6.04 kOe), while maintaining high B_r (12.85 kGs) and excellent temperature stability (β_20-120 = −0.553 %/°C). Microstructural analysis reveals that continuous grain boundary phases in the magnets with low B content provide efficient pathways for Dy diffusion, though excess CeFe₂ phases may hinder the diffusion process. In the magnets with high B content, fewer grain boundary phases force Dy to diffuse via less efficient lattice pathways, limiting the diffusion depth. The study confirms that 0.95 wt% B magnets, after Dy diffusion, exhibit the best overall performance, providing theoretical support for the development of low-cost, high-coercivity Ce-containing magnets.