Magnetic properties enhancement of hot-deformed NdFeB magnets by two different methods of CeNdCu diffusion

Two different ways were used to control the distribution of cerium for the enhancement of coercivity. One was by coating CeNdCu in the prepared magnet and annealing to make CeNdCu diffuse into the grain boundary to increase the coercivity, the other was by mixing CeNdCu with initial magnetic powders and then preparing the hot-deformed magnet. The SEM-EDS result indicates that cerium diffuses more easily into the main phase by the mixing way, while cerium is mainly distributed in the grain boundary via the coating way. The heat-treatment process may be one of the dominant influencing factors for the distribution of Ce. Multi-steps heat treatment in the mixing way, consisting of hot-pressing, hot-deforming and post heat process, easily introduces Ce into the main phase Nd2Fe14B, which forms the Ce2Fe14B shell resulting in the decrease of HA. But the coating way can ensure uniform dispersion of Ce in the grain boundary, which leads to the high coercivity.