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The 28th International Workshop on Rare Earth and Future Permanent Magnets and Their Applications (REPM2025)

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Nd-Fe-B magnets used in EVs require high coercivity to withstand high temperatures and high antimagnetic fields. One of the methods to improve the coercivity of hot-deformed Nd-Fe-B magnets without using heavy rare earth elements such as Dy and Tb is the grain boundary diffusion process using light rare earth elements [1], [2]. In this process, a eutectic alloy such as Nd-Cu is applied to the magnet surface followed by heat treatment at a low temperature of 500-700℃. This allows the eutectic alloy to diffuse from the surface to the interior of the magnet while inhibiting the growth of fine crystal grains, widening the grain boundary phase, weakening the magnetic interaction between the Nd2Fe14B particles resulting in an improvement in coercivity. Fig. 1(a) shows changes in remanence (Br) after Nd-Cu alloy diffusion, and Fig. 1(b) shows increases in coercivity (HcJ) from the base magnet. The decrease in Br due to grain boundary diffusion is constant regardless of HcJ of the base magnet. However, the larger the amount of increase in coercivity, the smaller the coercivity of the base magnet. This suggests that higher hard magnetic properties can be obtained by using a magnet with higher Br as the base magnet. Therefore, a base magnet with low RE composition is desirable. In this report, hot-deformed magnets with Br of 1.42 T at room temperature and HcJ of 553 kA/m at 150℃ and Hk/HcJ of 98% at 150℃ was used as the base magnet and Nd-Cu alloy was diffused into the grain boundary. The HcJ of the magnet was improved to 704 kA/m at 150℃ with Br of 1.39 T at room temperature without HREE. The Hk/HcJ is still maintained at 96% at 150℃, which is adequate for usage of EVs.

References
[1] H. Sepehri-Amin, T. Ohkubo, S. Nagashima, M. Yano, T. Shoji, A. Kato, T. Schrefl and K. Hono, Acta Mater. 61 (2013) 6622-6634
[2] H. Sepehri-Amin, Lihua Liu, T. Ohkubo, M. Yano, T. Shoji, A. Kato, T. Schrefl, and K. Hono, Acta Mater. 99 (2015) 297-306

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• Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International
  

Keyword: REPM2025, xEV, Nd-Fe-B magnet, HREE-free, Hot-deformed magnet, Grain boundary diffusion

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Publisher: National Institute for Materials Science (NIMS)

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Conference: REPM2025 (2025-07-27 - 2025-07-31)

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Manuscript type: Not a journal article

MDR DOI: https://doi.org/10.48505/nims.5646

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Updated at: 2025-08-20 12:30:57 +0900

Published on MDR: 2025-08-20 12:19:27 +0900