Realizing the efficient utilization of Tb resources and high coercivity in grain boundary diffusion Nd–Fe–B magnets: the synergistic effect of Cu and Tb

Abstract

The utilization of Cu micropowder as an auxiliary material presents a promising strategy to enhance the efficiency of heavy rare earth elements in grain boundary diffusion (GBD) processes. This study systematically investigates the composite addition strategies of Cu and a TbH₃ diffusion source (including mixed diffusion and stepwise diffusion) and their effects on the diffusion behavior of Tb. Compared to the original magnet, the coercivity of the TbH₃ GBD (T GBD), Cu + TbH₃ mixed diffusion (C + T GBD), and Cu–TbH₃ stepwise diffusion (C−T GBD) magnets increases by 6.67 kOe, 12.33 kOe, and 13.16 kOe, respectively. Notably, the Tb utilization efficiency in the C−T GBD magnet reaches 146% of that in the T-GBD magnet under Cu-auxiliary diffusion. Microstructural characterization and elemental distribution analysis reveal that the C−T GBD magnet exhibits the deepest Tb diffusion depth and highest Tb content distribution, forming extensive core(Nd₂Fe₁₄B)–shell[(Nd, Tb)₂Fe₁₄B] structures that effectively enhance the reverse domain nucleation field. Temperature stability testing shows superior high-temperature performance of stepwise diffusion magnets, with a coercivity temperature coefficient of −0.51%/°C and an irreversible magnetic flux loss of only 0.5% at 150 °C. This work provides theoretical and technical insights into high-efficiency GBD based on cooperative diffusion strategies of Cu and Tb.