Coercivity enhancement of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B powders by the diffusion of Nd–Cu eutectic alloys

We report the coercivity enhancement of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B nanocrystalline powders from 1321 to 1552 kA m−1 (19.5 kOe) by the grain boundary diffusion of Nd–Cu melts with hyper-eutectic compositions. A distinct Nd-rich grain boundary phase was observed after the diffusion process by scanning electron microscopy and transmission electron microscopy; however, atom probe tomography indicated that the change in composition of the grain boundary phase was not significant. The mechanism of the coercivity enhancement is discussed based on these results.