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Microstructure analysis of a Ga-doped NdFeB magnet with 2.0T coercivity

62nd Annual Conference on Magnetism and Magnetic Materials

XU Xiandong(NIMS),Zhanji Dong(Yantai Shougang Magnetic Materials Inc), KIM Tae-Hoon(NIMS),SASAKI Taisuke(NIMS),OHKUBO Tadakatsu(NIMS),HONO Kazuhiro(NIMS)

Abstract

Recently, Nakajima and Yamazaki reported that a trace addition of Ga (0.5 at.%) substantially enhanced the coercivity of Nd-Fe-B sintered magnets due to the physical isolation of Nd2Fe14B grains by the formation of Nd6Fe13Ga1 phase [1]. Our detailed microstructure investigations have shown that three types of grain boundary phases, i.e. Ia-3, amorphous and Nd6Fe13Ga phases, are all non-ferromagnetic [2]. Since Ga is rather expensive, there is a demand to optimize the Ga content. In this presentation, we report a microstructure and magnetic property of a high coercivity Nd-Fe-B sintered magnet with less addition of Ga.
The chemical composition of the sintered magnets used in this work was Nd11.52Pr3.20Fe77.12 Co0.96B5.55Cu0.21Al1.30Ga0.14. Microstructure observation was performed using a field emission SEM, Carl Zeiss Cross Beam 1540 EsB. STEM observation was performed using a FEI Titan G2 80-200 (S)TEM. Thin lamellas for the STEM observations were made by the FIB, FEI Helios Nanolab 650.
The as-sintered sample shows a coercivity, 0Hc, of 1.48 T, and the post-sinter annealing lead to the substantial coercivity increase to 2.01 T, which is higher than that containing 0.5at.% Ga [1]. BSE-SEM images show that the sample has the grain size of 3.3 µm in diameter, which is finer compared to the sample containing 0.5 at.% Ga (5.5 m) [1]. The grain boundary (GB) phase formed in the present sample is thinner than that in the sample containing 0.5 at.% Ga. In contrast to the 0.5 at.% Ga containing sample, the GB phase is formed uniformly and continuously (the c-plane GB phase contain about 55 at.% Nd+Pr and the AB-plane GB phase contain about 35 at.% Nd+Pr). We also found that the metallic Nd-rich phase at triple junctions in the present sample has a dhcp structure unlike the Ia-3 type phase observed in the sample containing 0.5at.% Ga [2]. This may suggest that the dhcp Nd is more beneficial for the uniform formation of the GB phase, giving rise to better decoupling of the hard magnetic grains.


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