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 Pr 70 Cu 30 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. • The diffusion effect is sensitive to the Ce content in Nd-Ce-Fe-B magnets. • The Ce substitution for Nd/Pr promotes the diffusion process of Pr 70 Cu 30 alloy. • Abnormal coarse grains enriched with Pr near the surface were formed after GBDP. • Both the coercivity and remanence increased after GBDP for Nd-Ce-Fe-B magnets.