Grain boundary diffusion behaviors of Dy/Tb elements in sintered (Pr, Nd Dy)-Fe-B magnets with varying Dy content

Heavy rare earth grain boundary diffusion is an effective method for preparing high performance sintered Nd-Fe-B permanent magnets. The composition of the NdFeB base materials is closely related to the diffusion depth of heavy rare earth elements. In this work, (Pr, Nd, Dy)-Fe-B sintered magnets with different Dy content were used as base magnets and high-performance magnets with core-shell structure were prepared by DyH/TbH grain boundary diffusion. The diffusion behaviors of heavy rare earth elements, magnetic properties and grain boundary phase structure of the diffused magnets were investigated systematically. In the TbH diffused magnets, Tb partially replaces Pr, Nd and Dy elements in the main phase grains, and forms (Pr, Nd, Dy, Tb)-rich shell in the surface layer of the matrix grains. Both the diffusion depth of Tb elements, the concentration of Tb at grain boundary and coercivity increment are improved with increasing Dy content. The difference in Dy concentration between the main phase and the grain boundary phase of DyH diffused magnet reduces with increased Dy content, which weakens the diffusion depth and thickness of Dy-rich shell. This work provides a certain guiding significance for the efficient utilization of heavy rare earth elements.