Coercivity enhancement of sintered Ce-substituted Nd-Fe-B magnets by grain boundary diffusion process of Tb

Abstract Grain boundary diffusion process (GBDP) of Tb on sintered Ce-substituted Nd-Fe-B magnets has been conducted by magnetron sputtering deposition of Tb film for coercivity enhancement. The microstructure and magnetic properties of the diffused (Nd,Ce)FeB magnets have been evaluated and the effect of diffusion temperature, time and Tb coating thickness on the Ce-substituted N35 magnets are discussed. The results show that a core-shell structure is formed around the main grains after GBDP, which promotes the coercivity enhancement of the magnets. A maximum coercivity enhancement from 10.9 kOe to 15.2 kOe is achieved in Ce-N35 magnets by deposition of 10 μm Tb films followed by diffusion processing at 900 ℃ for 300 min. The inhibition effect of Ce in GBDP of Tb is also evaluated using (Nd,Ce)FeB magnets with different Ce contents and discussed using diffusion model simulation implemented by Tb distributions through GD-OES. The rare earth element (REE)-rich nodes located at the triple junction of the grains may attribute to the Tb aggregation and the formation of TbFe2, resulting in the inhibition of further Tb diffusion.