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Coercivity and its thermal stability of Nd-Fe-B hot-deformed magnets enhanced by the eutectic grain boundary diffusion process

Acta Materialia, Vol.161, Pages 171-181

2018年12月1日(土)

Jiangnan Li, Lihua Liu, Hossein Sepehri-Amin, Xin Tang, TadakatsuOhkubo, Noritsugu Sakuma, Tetsuya Shoji,Akira Kato, SCHREFLThomas, Kazuhiro Hono ( https://doi.org/10.1016/j.actamat.2018.09.018 )

Abstract

Eutectic grain boundary diffusion process was applied to NdFeB hot-deformed magnet usingNd60Tb20Cu20 alloy, which resulted in a large coercivity enhancement from 0.87 T to 2.57 Twith a relatively small decrease in remanent magnetization from 1.50 T to 1.38 T. Improvedtemperature coefficient of coercivity from −0.493%°C−1 to −0.328%/°C−1 led to a highcoercivity of 1.47 T at 150 °C. The partial formation of Tb-rich shell on the surface of plateletshaped Nd2Fe14B grains while maintaining their ultra-fine grain size is the reasons for thesubstantial enhancement of the coercivity. Micromagnetic simulations suggested that a highercoercivity can be obtained when Tb-rich shell covers the c-plane surface interface of thegrains than that covering the side surface interfaces. Improvement of the thermal stability ofcoercivity was found to be due to the exchange decoupling of Nd2Fe14B grains and theformation of (Nd,Tb)2Fe14B shell. In the frame of Kronmüller equation and based on themicromagnetic simulations, the improvement of the thermal stability of coercivity is attributedto the decrease of Neff and increase of α induced by exchange decoupling of grains, as wellas the additional decrease of Neff induced by the formation of high-Ha shell.



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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