Optimization of grain boundary diffusion in Nd-Ce-Fe-B magnets through CeFe2 phase

Abstract

The REFe₂ phase in Ce-containing Nd-Ce-Fe-B magnets is considered detrimental to magnetic properties due to its soft magnetism, and the presence of the CeFe₂ phase hinders the diffusion of heavy rare earth elements. In this study, grain boundary diffusion (GBD) treatment was performed on commercial N40 sintered Nd-Ce-Fe-B magnets using Tb and Tb₇₀Cu₃₀ alloys, respectively. The results indicate that the CeFe₂ phases appear at the grain boundaries during grain boundaries diffusion, but there is a significant difference in the distribution and quantity of the CeFe₂ phase between Tb GBD magnets and Tb₇₀Cu₃₀ GBD magnets. Cu atoms are more likely to bind with Ce in the grain boundary phase, thereby suppressing the formation of CeFe₂ phase and improving the diffusion effect of Tb in Ce-containing magnets. Additionally, Cu broadens the grain boundaries, allowing for deeper diffusion of Tb. Although the substitution of Tb (30 wt%) by Cu in the Tb₇₀Cu₃₀ alloy, the Tb₇₀Cu₃₀ GBD magnet still achieves significant coercivity enhancement, nearly as well as the Tb GBD magnet. This work provides new prospects for the development of Nd-Ce-Fe-B magnets treated with grain boundary diffusion.