Magnetic Properties and Tb Diffusion of Sintered Nd–Fe–B Magnets by Suspension Plasma Spraying

For the first time, a TbF 3 coating as a diffusion source was prepared on the surface of sintered Nd–Fe–B magnets by suspension plasma spraying. A sintered Nd–Fe–B magnet with a high coercivity and low remanence loss was obtained. The uniform and dense coating favored grain-boundary diffusion of heavy rare-earth elements, which improved the coercivity of Nd–Fe–B magnets. The effect of grain-boundary diffusion and TbF 3 coating amount on the microstructure and magnetic properties of the magnet were studied. Optimal magnetic properties were obtained for a heat treatment of 900°C for 10 h, when the TbF 3 coating amount was 0.2132 mg/mm 2 . The coercivity reached 23.72 kOe with an increase of 60.16% compared with the original magnet, whereas the remanence did not decrease significantly. Microstructure analysis showed that a Tb-layer core–shell structure formed around the Nd 2 Fe 14 B grains after diffusion. The high magnetocrystalline anisotropy of the Tb core-shell structure formation improved the Nd–Fe–B magnet coercivity significantly. Therefore, the method of plasma spray grain-boundary diffusion is efficient and feasible