Microstructure and super-high coercivity of Tb-containing NdFeB magnets by diffusion with Tb metal and Pr-Al-Cu-Ga

A sintered NdFeB magnet with super-high coercivity of 46.21 kOe was successfully obtained by two-step diffusion with Tb metal and Pr-Al-Cu-Ga alloys. Tb-containing magnets with super-high coercivity were used as base magnets; coercivity increased from 35.86 to 44.51 kOe for the Tb-diffused magnet and 46.21 kOe for the magnet with Tb and Pr-Al-Cu-Ga diffusion. Microstructure analysis indicated that two-step diffusion resulted in Tb/Pr-rich double-shell structures, optimized grain boundary structure, and the enhancement of RE-rich grain boundary phases, which is the main reason for the enhancement of coercivity. The diffusion-induced variation of remanence was also discussed. This work provides insights into further breaking the coercivity limit of sintered NdFeB magnets.