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Microstructure of a Dy-free Nd-Fe-B sintered magnet with 2 T coercivity

Acta Materialia Volume 156

2018年9月1日(土)

Xiandong Xu, Taisuke Sasaki, Jiangnan Li,Hossein Sepehri-Amin,Tae-Hoon Kim, Tadakatsu Ohkubo, Thomas Schrefl,Kazuhiro Hono ( https://doi.org/10.1016/j.actamat.2018.06.037 )

Abstract

We investigated the microstructure of the Dy-free high coercivity sintered magnet that wasdeveloped by optimizing the chemical composition of Nd-Fe-B sintered magnet with 0.1 at.%Gadoping in order to understand the reasons for the high coercivity of μ0Hc = 2.0 T and theimproved squareness of 0.95 compared to a recently developed 0.5 at. %Ga doped magnet. Theas-sintered 0.1Ga sample shows a relatively high coercivity of 1.5 T owing to the finer grainsize of ∼3.3 μm and the higher Al concentration up to 1.3 at.% compared to post-sinterannealed 0.5Ga magnet that has a grain size of ∼5.5 μm and Al concentration of 0.9 at. %. Thepost-sinter annealing leads to a substantial coercivity increase from 1.5 to 2.0 T due to theformation of a thick and crystalline intergranular grain boundary (GB) phase containing 30-60 at.% of Nd. The trace Ga addition of 0.1 at.% improved the wettability of the liquids andfacilitated the formation of thick GB phase during the post-sinter annealing. The goodsquareness is mainly attributed to the ferromagnetic nature of the intergranular GB phase aswell as the strong crystal alignment to the easy axis. Finite element micromagnetic simulationsof the demagnetization processes of the models incorporating experimentally determined GBthickness and chemistry well explain the simultaneous achievement of the high coercivity andgood squareness observed in this magnet in contrast to the very poor squareness observed inthe post-sinter annealed 0.5Ga sample.



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文部科学省
元素戦略プロジェクト(活動紹介)
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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