Effect of heat-treatment on the microstructure and magnetic properties of Tb and Tb/Cu diffused Nd-Fe-B magnets

In this study, Tb and Tb/Cu diffusion sources were prepared using electrochemical deposition. The effects of different heat treatment processes on the grain boundary diffusion (GBD) behavior of Nd-Fe-B magnets were investigated, focusing on the solid-liquid phase separated diffusion process (SepD) and the solid-liquid phase simultaneous diffusion process (SimD). The best magnetic performance was achieved using the SepD process for the Tb/Cu-diffused magnet, exhibiting a coercivity of 2000 kA/m (an increase of 74.06 %) and a remanence of 1.299 T (an increase of 1.80 %). Research has revealed that the h -RE 2 O 3 → c -RE 2 O 3 phase transformation, the formation of core-shell (or anticore-shell) structure, as well as the optimization of the grain boundary phase are the main contributors for the enhanced coercivity. The formation of the c -RE 2 O 3 phase, with its low-lattice mismatch to the RE 2 Fe 14 B matrix, is the key reasons for the nearly unchanged remanence in the diffused magnets. After grain boundary diffusion process, the coercivity mechanism of diffusion magnet is the magnetic domain nucleation inversion.