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Reduction in critical heavy rare earth (HRE) elements such as Dy and Tb in NdFeB-based magnets for coercivity enhancement at the high operating temperature in E-motors is important for sustainable green energy transition. In this work, we maximize HRE utilization by selective hardening of areas in the magnet such as corners or edges that are highly susceptible to demagnetization, as demonstrated by Finite Element magnetostatics simulation on an internal permanent magnet synchronous traction motor for electric vehicles (Fig. 1a). Commonly industrially used HRE source TbHx as well as complex multicomponent Tb-containing alloys such as Tb10Pr60(Cu,Al,Ga)30 are investigated on commercial grade NdFeB-based sintered magnets. For Tb hydride not only is the HRE utilization less efficient, but also the diffusion is more sluggish resulting in shorter diffusion depth. Highly efficient Tb utilization using small HRE amount comparable to trace elements added to commercial sintered magnets (e.g. Al, Cu, Ga) and good hightemperature performance is reached. Diffusing 0.4 wt.% Tb results in coercivity of 1014 kA/m at 120 °C with only minor reduction in remanence from around 1.45 T in the initial magnet to 1.43 T after GBDP. To shed light on the HRE diffusion and local magnetic hardening, spatial coercivity mapping was done to investigate the local coercivity enhancement. The results are graphically illustrated in Fig. 1b. Corners clearly show the highest coercivity reaching nearly 1600 kA/m corresponding to 587 kA/m enhancement compared to the initial magnet. As expected for a diffusion-governed process, coercivity decrease is proportional to the distance from the diffusion source (corners).

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• Creative Commons BY Attribution 4.0 International
  

Keyword: REPM2025, permanent magnet, Nd2Fe14B, heavy rare earth, grain boundary diffusion, terbium

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.5644

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Updated at: 2025-08-20 12:30:47 +0900

Published on MDR: 2025-08-20 12:19:23 +0900