Ce-La-Tb-Cu grain boundary diffusion for Nd-Fe-B magnets: Toward obtaining high coercivity and high electric resistivity

Simultaneously enhancing the coercivity and electric resistivity of sintered Nd-Fe-B magnets is important for high-performance motor rotors. However, this is still a difficulty for the industry, and the underlying physical mechanisms are still unclear. In this work, the coercivity and resistivity of sintered Nd-Fe-B magnets are successfully improved by grain boundary diffusion (GBD) based on Ce-Tb-Cu and Ce-La-Tb-Cu alloy diffusion sources. The results show that the coercivity and resistivity of the magnet are improved after Ce_xTb_70-xCu₃₀ (x = 25, 42.5, 60) diffusion. The coercivity of the diffused magnets increased from 14.75 to 15.77–22.04 kOe, and the resistivity increased by 0.29–0.84 Ω·μm. On this basis, La was introduced and Ce_yLa_4yTb_70–5yCu₃₀ (y = 5, 8.5, 12) alloy powder was used as diffusion sources. The coercivity increased by 10.64 kOe and the resistivity increased by 0.64 Ω·μm. The introduction of Ce and La can effectively control the diffusion behavior of Tb and improve the coercivity and thermal stability of the magnets. Combined with the results from microstructure characterizations and first-principles calculations, the introduced high-abundance rare earths of Ce and La can promote the formation of high-resistivity oxides in grain boundaries and triple junctions, which has a certain isolation effect between the 2:14:1 hard magnetic grains and improved the resistivity of the magnet. This work gives a reasonable approach to fully use the high-abundance rare earths and enhancing the combined electromagnetic performance of Nd-Fe-B magnets.