A novel two-step grain boundary diffusion process using TaF5 and Pr70Cu15Al10Ga5 for realizing high-coercivity in Nd-Fe-B-sintered magnets without use of heavy rare-earth

IF 8.3 1区 材料科学 Q1 MATERIALS SCIENCE, MULTIDISCIPLINARY Acta Materialia Pub Date : 2024-12-22 DOI:10.1016/j.actamat.2024.120660
Seol-mi Lee, Ganghwi Kim, Ki-Suk Lee, Sumin Kim, Tae-Hoon Kim, Sang-hyub Lee, Dong-Hwan Kim, Wooyoung Lee, Jung-Goo Lee
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Abstract

To achieve high-coercivity in Nd-Fe-B-sintered magnets without relying on the use of heavy rare-earth (HRE), developing an HRE-free grain-boundary-diffusion-process (GBDP) using the light rare-earth, Pr, is highly desired. The key factor for achieving high-coercivity via Pr-GBDP is to increase the Pr-concentration of Pr-rich shell by reducing its thickness, and this can be realized by inhibiting the chemically induced liquid film migration (CILFM) that occurs to form the shell. Herein, for the first time, we report achievement of high-coercivity of 2.35 T without using HRE by developing CILFM-inhibited two-step GBDP that uses TaF5 to form a intergranular precipitate (PPT) and Pr70Cu15Al10Ga5 to form a Pr-rich shell in the 1st- and 2nd-steps, respectively. Due to the formation of hexagonal-TaB2 intergranular PPT during the 1st-GBDP, the CILFM is inhibited during the 2nd-GBDP, thereby reducing the grain size and forming the thinner shell with higher Pr-concentration in the magnets. As a result, the μ0Hc of two-step GBDP magnets (2.35 T) is considerably higher than that of magnets GBD-treated with Pr70Cu15Al10Ga5 alone (1.85 T). A micromagnetic simulation shows that the nucleation field at the interface between the 2-14-1 grain and Nd-rich phase in two-step GBDP magnets increases by such a thinner and higher Pr-concentration shell. Furthermore, due to the CILFM inhibition, the number of Pr atoms consumed for the shell formation near the magnet surface reduces in the two-step GBDP magnets, resulting in an increased GBD-depth of Pr, and this is another contributor for realizing a high-coercivity in magnets via the HRE-free two-step GBDP.

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使用 TaF5 和 Pr70Cu15Al10Ga5 的新型两步晶界扩散工艺,在不使用重稀土的情况下实现 Nd-Fe-B 烧结磁体的高矫顽力
为了在不依赖使用重稀土(HRE)的情况下实现钕铁硼烧结磁体的高矫顽力,开发一种使用轻稀土 Pr 的无 HRE 晶界扩散过程(GBDP)是非常必要的。通过 Pr-GBDP 实现高矫顽力的关键因素是通过减少富含 Pr 的外壳厚度来提高其 Pr 浓度,而这可以通过抑制形成外壳的化学诱导液膜迁移(CILFM)来实现。在此,我们首次报告了在不使用 HRE 的情况下,通过开发 CILFM 抑制的两步 GBDP(在第一步和第二步中分别使用 TaF5 形成晶间沉淀(PPT)和 Pr70Cu15Al10Ga5 形成富含镨的外壳),实现了 2.35 T 的高矫顽力。由于在第 1-GBDP 阶段形成了六方-TaB2 晶间沉淀(PPT),在第 2-GBDP 阶段抑制了 CILFM,从而减小了晶粒尺寸,并在磁体中形成了具有较高 Pr 浓度的较薄磁壳。因此,两步 GBDP 磁体的 μ0Hc 值(2.35 T)大大高于单独使用 Pr70Cu15Al10Ga5 进行 GBD 处理的磁体的 μ0Hc 值(1.85 T)。微磁模拟显示,在两步 GBDP 磁体中,2-14-1 晶粒和富钕相界面处的成核场会因更薄和更高 Pr 浓度的外壳而增加。此外,由于 CILFM 抑制作用,在两步 GBDP 磁体中,磁体表面附近形成磁壳所消耗的镨原子数量减少,导致镨的 GBD 深度增加,这也是通过无 HRE 两步 GBDP 实现磁体高矫顽力的另一个原因。
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来源期刊
Acta Materialia
Acta Materialia 工程技术-材料科学:综合
CiteScore
16.10
自引率
8.50%
发文量
801
审稿时长
53 days
期刊介绍: Acta Materialia serves as a platform for publishing full-length, original papers and commissioned overviews that contribute to a profound understanding of the correlation between the processing, structure, and properties of inorganic materials. The journal seeks papers with high impact potential or those that significantly propel the field forward. The scope includes the atomic and molecular arrangements, chemical and electronic structures, and microstructure of materials, focusing on their mechanical or functional behavior across all length scales, including nanostructures.
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