Effect of Ce content on the magnetic properties and microstructure of sintered Nd-Ce-Fe-B magnets after Pr70Cu30 alloy diffusion

Grain boundary diffusion process (GBDP) with Pr70Cu30 alloy was performed on sintered Nd-Ce-Fe-B magnets with different Ce contents (0 wt%, 5 wt%, 10 wt% and 15 wt%). The coercivities of the original magnets were 1053 kA/m (Ce: 0 wt%), 912 kA/m (Ce: 5 wt%), 915 kA/m (Ce: 10 wt%) and 732 kA/m (Ce: 15 wt%). After GBDP the coercivities were 1390 kA/m (Ce: 0 wt%), 1074 kA/m (Ce: 5 wt%), 937 kA/m (Ce: 10 wt%) and 849 kA/m (Ce: 15 wt%). Compared with the original magnets the coercivity increments were 337 kA/m (32%), 162 kA/m (17.8%), 22 kA/m (2.4%) and 117 kA/m (16%) for the magnets with Ce contents of 0 wt%, 5 wt%, 10 wt% and 15 wt%, respectively after GBDP. The Ce substitution for Nd/Pr promotes the diffusion process while the coercivity increment decreases due to the formation of abnormal coarse grains near the magnet surface. After GBDP the remanence increments were -0.01 T, 0.02 T, 0.04 T, 0.05 T for the Ce0, Ce5, Ce10 and Ce15 magnets, respectively. The improved remanence of the Nd-Ce-Fe-B magnets was attributed to the formation of Pr-rich grains near the magnet surface and the Pr-rich shells in the grain boundaries of the inner grains. The finding in this work reveals that for sintered Nd-Ce-Fe-B magnets the effect of GBDP is sensitive to the Ce content. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

Grain boundary diffusion process (GBDP) can improve the coercivity and remanence of sintered Nd-Ce-Fe-B magnets. Ce substitution promotes the diffusion process, but excessive Ce content leads to the formation of abnormally large grains on the magnet surface.