Impact of Nd–Cu diffusion on microstructure and coercivity in hot-pressed and die-upset nanocomposite magnets

The microstructure evolution in hot-pressed and die-upset magnets was studied to clarify the impact of Nd–Cu diffusion on microstructure and coercivity. It was found that Nd–Cu diffusion mainly occurs at the interface of the raw powders during the hot-pressing process. In the die-upsetting process, grain boundary diffusion is main reason for the homogeneous distribution of Nd–Cu. Moreover, Nd–Cu grain boundary diffusion decoupling the hard phases, grain morphology and the presence of Nd2O3 contribute to the higher coercivity in die-upset magnets with low height reduction.