Comparisons of Dy Utilization Efficiency by DyH_x Grain Boundary Addition and Surface Diffusion Methods in Nd-Y-Fe-B...

Using the heavy rare earth Dy element to improve coercivity is the most common solution for hindering the reduction in magnetic properties in the Nd-Fe-B magnet, and the effective utilization of Dy has become the focus of research in industrial society. In this work, we investigated the influence of DyH_x addition and diffusion methods on the microstructure, magnetic performance, and thermal stability of the Nd-Y-Fe-B magnet with a Y-rich core structure. The coercivity of the DyH_x addition magnet increases from 9.45 kOe to 15.51 kOe when adding 1.6 wt.% DyH_x, while the DyH_x diffusion magnet increases to 15.15 kOe. According to the analysis of the microstructure and elemental distribution, both Dy-rich shells were basically formed due to the diffusion process of Dy atoms. The Dy-rich shell in the DyH_x addition magnet was similar with the original core-shell structure in the Nd-Y-Fe-B magnet. However, the distinct dual-shell structure consisting of a thinner Dy-rich shell and a Y-lean shell was constructed in the DyH_x diffused magnet, contributing to the superior coercivity increment and Dy utilization efficiency. Furthermore, the remanence of the DyH_x diffused magnet is up to 12.90 kG, which is better than that of the DyH_x addition magnet (12.59 kG), due to fewer Dy atoms entering the 2:14:1 matrix grain to cause the antiferromagnetic coupling with Fe atoms. Additionally, the thermal stability of the DyH_x diffusion magnet is also better than that of the DyH_x addition magnet, owing to the elevated coercivity at room temperature, which expands the application range of the Nd-Y-Fe-B magnet to a certain extent.