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Microstructure and magnetic anisotropy with different HD conditions in d-HDDR process ofNd-Fe-B powders

The 25th International Workshop on Rare-Earth and Future Permanent Magnets and theirApplications (REPM2018),2018.8.26-30, Beijing,China

2018年8月29日(水)

Masao Yamazaki (Aichi Steel Corp./Tohoku University), Takashi Horikawa, Chisato Mishima(Aichi Steel Corp.) Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto (Tohoku University)

Abstract

The dynamic hydrogen disproportionation desorption recombination (d-HDDR) process is one of the methods forthe production of anisotropic Nd-Fe-B magnet powders [1]. However, the origin of anisotropy induced by the d-HDDR has not been clarified yet. In this study, a systematic investigation of the relationship betweenmicrostructure after the hydrogen disproportionation (HD) and magnetic properties after the d-HDDR treatmentwith different HD treatment conditions were performed. Nd12.5Fe80.6B6.4Ga0.3Nb0.2 powder (≤ 212 μm) was usedas a starting material. In the HD stage, the powder was heated at 1093 K for 1 min ~ 10 h under 30 or 100 kPa ofhydrogen atmosphere. After the HD treatment, the sample powder was subsequently heated at the sametemperature as HD stage under vacuum to complete desorption recombination (DR) process. The degree ofanisotropy λ was defined as λ =(Jr-Jrhard)/Jr ,where Jr and Jr hard represent residual magnetic polarizationsobtained from the VSM measurements with an applied magnetic field parallel and perpendicular to the alignmentdirections, respectively. Figure 1 represents HD time dependence of λ after d-HDDR showing a decreasingtendency of λ with increasing HD time. The powders HD treated for 0.5 h at 30 kPa and 1 min at 100 kPa showedhigher anisotropy and in the microstructures of these samples, lamellar-like structure comprising of α-Fe andNdH2 was observed. When the HD time was long, their morphology became coarse stripe-shaped or sphericalstructures. In the powder HD treated for 10 h at 30 kPa, both coarse stripe-shaped and spherical structures wereobserved and this powder showed magnetic anisotropy after d-HDDR. By contrast, after the HD treatment for 10 hat 100 kPa, only spherical structure was observed and after d-HDDR the powder became isotropy. This resultindicates that the lamellar-like and coarse stripe-shaped structures are related to high magnetic anisotropy in d-HDDR process.

その他特記事項

This study is partially supported by the Elemental Strategy Initiative Center forMagnetic Materials (ESICMM) under the outsourcing project of MEXT, JAPAN.


研究活動

文部科学省

文部科学省
元素戦略プロジェクト(活動紹介)
NIMS磁石パートナーシップ

元素戦略拠点

触媒・電池元素戦略拠点
触媒・電池元素戦略研究拠点 (京都大学)
東工大元素戦略拠点
東工大元素戦略拠点 (東京工業大学)
構造材料元素戦略研究拠点
構造材料元素戦略研究拠点 (京都大学)
高効率モーター用磁性材料技術研究組合
高効率モーター用 磁性材料技術研究組合