Optimization of the grain boundary diffusion process by doping gallium and zirconium in Nd-Fe-B sintered magnets

As the channel for grain boundary diffusion (GBD) in Nd-Fe-B magnets, grain boundary (GB) phases have a very important effect on GBD. As doping elements that are commonly used to regulate the GB phases in Nd-Fe-B sintered magnets, the influences of Ga and Zr on GBD were investigated in this work. The results show that the Zr-doped magnet has the highest coercivity increment (7.97 kOe) by GBD, which is almost twice that of the Ga-doped magnet (4.32 kOe) and the magnet without Ga and Zr (3.24 kOe). Microstructure analysis shows that ZrB2 formed in the Zr-doped magnet plays a key role in increasing the diffusion depth. A continuous diffusion channel in the magnet can form because of the presence of ZrB2. ZrB2 can also increase the defect concentration in GB phases, which can facilitate GBD. Although Ga can also improve the diffusion depth, its effect is not very obvious. The micromagnetic simulation based on the experimental results also proves that the distribution of Tb in the Zr-doped magnet after GBD is beneficial to coercivity. This study reveals that the doping elements Ga and Zr in Nd-Fe-B play an important role in GBD, and could provide a new perspective for researchers to improve the effects of GBD.