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

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Anisotropic hot-deformed Nd-Fe-B magnets have high coercivity without the addition of heavy rare earth elements (HREEs) due to their fine crystal grains[1]. Magnetic properties of the hot-deformed magnet depend on the quality of melt spun ribbons as the starting material. If coarse grains exist in the ribbons, crystal grains in the hot-deformed magnet would become coarse during the hot-deformation process resulting in coercivity
decrease[2]. Generally, melt spun ribbons have a large grain size distribution, making it a challenge to produce ribbons with homogeneous grains. In this study, we focused on producing high quality melt spun ribbons which have finer and more homogeneous crystal grains to obtain high-performance hot-deformed magnets without HREEs.

The ribbons, composed of Nd13.7Febal.Co1.5Ga0.5B5.6 and Nd13.9Febal.Co1.5Ga0.5B5.6 (at.%), were fabricated using a single-wheel melt spinner. Here, nozzle diameter, differential pressure and wheel speed were optimized. Ribbons were crushed into flake powders and sieved to be between 53 and 355μm. The hot-deformed magnets were produced by hotpress followed by hot extrusion. The magnetic properties of the melt spun ribbons and the hot-deformed magnets were measured by vibrating sample magnetometer (VSM) and BH tracer, respectively. Microstructure of fractured surface of ribbons and polished surface of the hot-deformed magnets were characterized by field emission scanning electron microscopy (FE-SEM). The crystal grain size and the distribution were determined from SEM images using deep learning method.

The ribbon was estimated to have nano-crystalline structure from the demagnetization curve. The median grain size of the conventional ribbon was around 45 nm, however grains of around 37 nm was obtained by optimizing the melt spinning conditions in this study. The grain size distribution index was 4% smaller than the conventional one, which means the grains became more homogeneous. The difference in the grain size between free side and wheel side of the ribbon was also small. One of the magnetic properties of the hot-deformed magnets showed the coercivity of 1725 kA/m at room temperature. Besides, coercivity at 150 ℃ showed 720 kA/m. The coercivity at 150℃ was 14% higher than the conventional hot-deformed magnets. These results indicate that finer and more homogeneous grain in melt spun ribbons is crucial to obtain high-performance HREEs free anisotropic Nd-Fe-B hot-deformed magnets.

References:
[1] K. Hioki, Sci. Technol. Adv. Mater. 22 (2021): 72-84
[2] J. Liu et al., Acta Materialia, 82 (2015): 336-343

権利情報:

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

キーワード: REPM2025, Permanent magnet, Nd-Fe-B, Hot-deformed magnet, Heavy rare earth free, Melt spinning

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

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原稿種別: 論文以外のデータ

MDR DOI: https://doi.org/10.48505/nims.5654

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更新時刻: 2025-08-20 12:30:41 +0900

MDRでの公開時刻: 2025-08-20 12:19:32 +0900