Anisotropic Consolidation Behavior of Isotropic Nd–Fe–B HDDR Powders During Hot-Deformation

Cha, Hee-Ryoung; Yoo, Jae-Gyeong; Jeon, Kwang-Won; Baek, Youn-Kyoung; Kwon, Hansang; Lee, Dong−Yun; Lee, J. G.

doi:10.1109/tmag.2017.2705107

Cited by 3 publications

(7 citation statements)

References 32 publications

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“…To verify the magnetic performance of the magnets developed in this work, the H cj and 4πM r of the HP-HDDR LC and HP-HDDR HC magnets are compared with those of Nd-Fe-B hot-pressed, hot-deformed, and bonded magnets produced from anisotropic HDDR powders reported in other studies [15,[21][22][23][36][37][38][39], as shown in Figure 7. The hot-pressed magnets developed in this work (HP-HDDR LC ) exhibited higher 4πM r than those of the hot-pressed and bonded magnets but showed lower 4πM r than those of the hot-deformed magnets reported in other studies.…”

Section: Resultsmentioning

confidence: 99%

“…The hot-deformation process, which consists of a hot-press step and a subsequent hot-deformation step [16,17], seems to be a promising process for producing high-H cj HDDR magnets because it specializes in the densification of ultrafine-grained Nd-Fe-B powders such as HDDR and melt-spun powders [18][19][20][21]. According to the current investigations [22,23], the HDDR magnets, comprising 400 ± 100 nm-sized 2-14-1 grains surrounded by more continuous Nd-rich GBPs, can be obtained by the hot-deformation of HDDR powders [22,23].…”

Section: Introductionmentioning

confidence: 99%

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Design of High-Remanence Nd-Fe-B Hot-Pressed Magnets by Manipulating Coercivity of Hydrogenation-Disproportionation-Desorption-Recombination Treated Anisotropic Precursors

Yoo,

Kim,

Cha

et al. 2023

Materials

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We propose a method of manipulating the coercivity of anisotropic hydrogenation-disproportionation-desorption-recombination (HDDR) powders to fabricate high-remanence and fine-grained Nd-Fe-B magnets using only hot-pressing without a subsequent hot-deformation process. By reducing the Nd content of anisotropic HDDR precursors such that their coercivity (Hcj) is lowered, the c-axis of each HDDR particle is well-aligned parallel to the direction of the applied magnetic field during the magnetic alignment step. This is because the magnetic repulsive force between adjacent particles, determined by their remanent magnetization, decreases as a result of the low coercivity of each particle. Therefore, after hot-pressing the low-Hcj HDDR powders, a significantly higher remanence (11.2 kG) is achieved in the bulk than that achieved by hot-pressing the high-Hcj HDDR powders (8.2 kG). It is clearly confirmed by the large-scale electron backscatter diffraction (EBSD) analysis that the alignment of the c-axis of each anisotropic HDDR particle in the bulk is improved when low-Hcj HDDR powders are used to fabricate hot-pressed magnets. This coercivity manipulation of HDDR powders can be a helpful method to expand the use of HDDR powders in fabricating anisotropic Nd-Fe-B bulk magnets.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Design of High-Remanence Nd-Fe-B Hot-Pressed Magnets by Manipulating Coercivity of Hydrogenation-Disproportionation-Desorption-Recombination Treated Anisotropic Precursors

Yoo,

Kim,

Cha

et al. 2023

Materials

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“…During the HD process, the Nd 2 Fe 14 B grains are able to align along the c-axis parallel to the pressing direction, which enhances the remanence (B r ) and maximum energy product ((BH) max ) [14]. Finegrained HDDR powders can be excellent raw materials for anisotropic HD magnets [15,16], but recent researches suggested that two major obstacles still remained to be addressed: one is the relatively low coercivity (H cj ) compared to sintered Nd-Fe-B magnet [17], and the other is the poor mechanical properties caused by coarse grains with high shape anisotropy after excessive deformation (larger than 70%) [18].…”

Section: Introductionmentioning

confidence: 99%

“…In order to solve the above-mentioned problems, we note that current HP magnets used as precursors for HD processes are all magnetically isotropic [16,17,21,22]. If anisotropic magnets are used as precursors, it is possible to obtain good caxis texture with less height reduction.…”

Section: Introductionmentioning

confidence: 99%

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Pre-orientation sintering: an alternative process to prepare high-performance anisotropic Nd–Fe–B HDDR magnets

Wang,

Zhao,

Pan

et al. 2023

J. Phys. D: Appl. Phys.

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Hydrogen–disproportionation–desorption–recombination (HDDR) Nd–Fe–B magnetic powders are promising to prepare bulk anisotropic magnets, but high magnetic performance has not been achieved due to the absence of an Nd-rich phase in the powder and the low degree of orientation of the bulk magnets. In this study, an alternative process of pre-orientation sintering via magnetic alignment followed by spark plasma sintering was proposed to prepare the precursor of hot-deformation (HD) magnets, and a high maximum energy product of 294 kJ m−3 was achieved in the HD magnet with a relatively low height reduction of 35%, then an improved coercivity of 1107 kA m−1 could be obtained followed by a grain boundary diffusion of Pr40Tb30Al20Cu10. Microstructure analysis indicates that pre-orientation of HDDR powders facilitates grain rotation and alignment during the HD process, thereby reducing the minimum deformation ratio. It helps to obtain the deformed grains with lower shape anisotropy and smaller grain size, enabling a good compatibility of magnetic and mechanical behaviors. In-situ Lorentzian transmission electron microscopy results show that the magnetic domains have been strongly fixed by the thick intergranular RE-rich phase and the fully Tb-diffused grains, which contributes to the improved coercivity after grain boundary diffusion. This study provides a guiding significance for the preparation of the anisotropic Nd–Fe–B HDDR magnets with optimized performance.

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Coercivity enhancement in Dy-free HDDR Nd-Fe-B powders by the grain boundary diffusion of Zn

Liu

Kong

et al. 2021

Journal of Magnetism and Magnetic Materials

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Anisotropic Consolidation Behavior of Isotropic Nd–Fe–B HDDR Powders During Hot-Deformation

Cited by 3 publications

References 32 publications

Design of High-Remanence Nd-Fe-B Hot-Pressed Magnets by Manipulating Coercivity of Hydrogenation-Disproportionation-Desorption-Recombination Treated Anisotropic Precursors

Design of High-Remanence Nd-Fe-B Hot-Pressed Magnets by Manipulating Coercivity of Hydrogenation-Disproportionation-Desorption-Recombination Treated Anisotropic Precursors

Pre-orientation sintering: an alternative process to prepare high-performance anisotropic Nd–Fe–B HDDR magnets

Coercivity enhancement in Dy-free HDDR Nd-Fe-B powders by the grain boundary diffusion of Zn

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