Magnetic properties and Tb diffusion of sintered Nd-Fe-B magnets by suspension plasma spraying

For the first time, a TbF3 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 TbF3 coating amount on the microstructure and magnetic properties of the magnet were studied. Optimal magnetic properties were obtained for a heat treatment of 900 degrees C for 10 h, when the TbF3 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 Nd2Fe14B 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.