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Macroscopically heterogeneous grain boundary diffusion process for efficient coercivity enhancement of Nd–Fe–B magnets

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Abstract

Grain boundary diffusion (GBD) is an effective process to enhance coercivity for Nd–Fe–B magnets with relatively low consumption of expensive heavy rare earths (HREs). For conventional GBD, the surface of the magnet is evenly covered by diffusion source, followed by diffusion heat treatment. In this work, a macroscopically heterogeneous GBD (MHGBD) process is proposed in order to further reduce the use of HRE resource. Based on the micromagnetic simulations, magnetically strengthening the edge area of the magnet is more effective than strengthening the center area in terms of coercivity enhancement for whole magnet. Hence, the HRE-based diffusion source was used for enhancing the edge area and the light rare-earth-based source was used for the center area. In details, Tb70Al20Cu10 and Pr70Al20Cu10 diffusion sources were covered at the edge and center areas of the two c-planes of a sintered Nd–Fe–B magnet, respectively. After the MHGBD by using Tb70Al20Cu10/Pr70Al20Cu10 (1:1, at.%), the magnet exhibits the increased coercivity from 1182 to 1911 kA/m. For comparison, the homogeneous diffusion of HRE-based Tb70Al20Cu10 source only enhances the coercivity to 1798 kA/m. The microstructure characterizations indicated that diffusion source of Tb70Al20Cu10 can form Tb-rich shells with high anisotropy field on the surface of Nd2Fe14B grains, and Pr70Al20Cu10 can provide more liquid grain boundary phase for GBD. The synergistic effect between these two sources improves the infiltration of Tb at the edge area of the magnet. Compared with the homogeneous Tb70Al20Cu10 diffusion, MHGBD process can not only exhibit higher diffusion efficiency, but also enhance the performance/cost ratio of the diffused magnets, evident by the increased coercivity enhancement per unit source from 0.23 to 0.51 kA m−1/($/kg).

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Acknowledgements

This work is supported by National Natural Science Foundation of China (No. U21A2052) and Jiangxi Provincial Key Science and Technology R&D Project (No. 20203ABC28W006).

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  1. Jiayi He and Wenyue Song contributed equally in this work.

Authors and Affiliations

  1. School of Materials Science and Engineering, South China University of Technology, Guangzhou, 510640, China

    Jiayi He, Wenyue Song, **angyi Liu, Wenbing Fan, Bang Zhou, Zhigao Yu, Jiali Cao, Hongya Yu, **chun Zhong & Zhongwu Liu

  2. JL MAG Rare-Earth Co., Ltd, Ganzhou, 341000, China

    Huayun Mao

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Contributions

JH was involved in conceptualization, methodology, formal analysis, investigation, writing—original draft, writing—review and editing. WS contributed to conceptualization, methodology, formal analysis, investigation, writing—original draft. XL was involved in software, investigation, data curation, validation. WF, BZ, ZY and JC contributed to investigation, data curation, validation. HY and XZ were involved in resources, visualization. ZL contributed to writing—review and editing, supervision, funding acquisition, project administration. HM was involved in resources.

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Correspondence to Zhongwu Liu.

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He, J., Song, W., Liu, X. et al. Macroscopically heterogeneous grain boundary diffusion process for efficient coercivity enhancement of Nd–Fe–B magnets. J Mater Sci 58, 5023–5036 (2023). https://doi.org/10.1007/s10853-023-08314-9

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