A tailored two-step process enabling high efficiency light rare earth diffusion in Ce-rich Nd–Ce–Fe–B magnet

Abstract

Developing a grain boundary diffusion process for Ce-rich Nd–Ce–Fe–B magnets by light rare earth remains a challenge. The underlying mechanism that limits the coercivity enhancement of Nd–Ce–Fe–B magnets by Pr80Al10Ga10 alloy diffusion is revealed in this work. The conventional grain boundary diffusion can promote the formation of a Pr-rich phase at the triple junctions but fails to achieve continuous grain boundary for magnetic isolation. The diffusion of Pr into the (Nd, Ce)2Fe14B grains is accompanied by the substitution of Nd and migration of Ce, which limits the increase in magnetic anisotropy field in the grain surface. To solve this problem, we propose a two-step diffusion approach to improve the diffusion efficiency of Pr80Al10Ga10 alloy. A high-temperature diffusion at 900 °C is employed to construct a Pr-rich shell with a high anisotropy field around main phase grains, followed by low-temperature diffusion at 800 °C to establish continuous non-magnetic grain boundary phases. By this approach, a coercivity enhancement of 4.3 kOe has been obtained in an Nd–Ce–Fe–B magnet with 26 wt. % Ce substitution for Nd. This work provides a scalable route for fabricating high-performance and cost-effective Ce-rich Nd–Ce–Fe–B magnets by light rare earth diffusion.