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Jae-Gyeong Yoo,Tae-Hoon Kim,Hee-Ryoung Cha,Yang-Do Kim,Jung-Goo Lee 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
The hot-deformation process is the most promising industrial process to fabricate fine-grained anisotropic Nd-Fe-B bulk magnets using melt-spun or HDDR powders. However, the problem of the hot-deformed magnets produced from the isotropic melt-spun powders is that an abnormal grain growth occurs during the hot-deformation process or the grain boundary diffusion process due to the fine nature of grains in the initial melt-spun powders. To use the isotropic HDDR powders with a relatively larger grain size as an initial powder is an effective way to fabricate the anisotropic hot-deformed magnets while suppressing the abnormal grain growth. However, the hot-deformed magnet produced from isotropic HDDR powders is difficult to obtain high remanence, Br. Because the [001] texture is not well developed during the hot-deformation due to the higher deformation resistance of the HDDR powders. Therefore, magnetically aligning the anisotropic HDDR powders before the densification can be a great solution for achieving higher Br in the magnets. In addition, if the HDDR powders can be magnetically well aligned before the densification, the fine-grained anisotropic bulk magnet could be obtained by the hot-press alone without undergoing subsequent die-upsetting process. Thus, in this study, we fabricated the anisotropic Nd-Fe-B hot-pressed using the anisotropic HDDR powders aligned by a pulsed magnetic field, and observed the influences of the magnetic and microstructural properties of initial HDDR powders on the magnetic alignment and hot-press behaviours. Especially, higher Br is obtained after the hot-press of the anisotropic HDDR powders when the remanence of the HDDR powders are controlled to be lower. This implies that higher-remanence HDDR powders generate stronger local magnetic field during the magnetic alignment, thereby disrupt the alignment of adjacent particles as observed by R. Soda et al. A detailed influences of the magnetic and microstructural properties of initial HDDR powders on the magnetic alignment and hot-press behaviours will be discussed, and a method to further increase the remanence of the hot-pressed magnets when align the anisotropic HDDR powder by pulsed magnetic field will be proposed based on the results. 〈그림 본문참조〉