Coercivity enhancement of hot-pressed magnet prepared by HDDR Nd-Fe-B powders using Pr-Cu eutectic alloys diffusion

The effect on the Nd-rich phase distribution of the ingot for hydrogenation-disproportionation-desorption-recombination (HDDR) powders was studied. Coercivity of HDDR powders was elevated to 1.64 T by crushing the ingot into particles and annealing at 800 °C for 18 h. HDDR processed Nd-Fe-B powders blended with Pr-Cu powders and annealed at 580 °C for 3 h were hot-pressed to obtain fully dense magnets. The microstructure evolution in hot-pressed HDDR magnets proved the impact of Pr-Cu diffusion on coercivity that the coercivity of hot-pressed magnets was improved to 1.55 T significantly. Backscatter electron microscopy and transmission electron microscopy observations revealed that the variation in coercivity owing to the diffusion of Pr-Cu along the grain boundary with heat treatment. L-TEM images illustrated the thicker grain boundary layer can pin the motion of the domain wall more effectively, resulting in a higher coercivity in HP magnets.