Attaining high magnetic performance in as-sintered multi-main-phase Nd-La-Ce-Fe-B magnets: Toward skipping the post-sinter annealing treatment
Attaining high magnetic performance in as-sintered multi-main-phase Nd-La-Ce-Fe-B magnets: Toward skipping the post-sinter annealing treatment
复制标题
在烧结态多主相 Nd-La-Ce-Fe-B 磁体中实现高磁性能：跳过烧结后退火处理
DOI：
10.1016/j.actamat.2019.03.005
复制
发表时间：
2019-05-01
期刊：
影响因子：
9.4
通讯作者：
Bai, Guohua
中科院分区：
文献类型：
--
作者：
Jin, Jiaying;Yan, Mi;Bai, Guohua
烧结后两步退火（PSA）工艺因其普遍适用性，已成为提高Nd-Fe-B系烧结磁体矫顽力的最有效方法之一。本文报道了一种特殊的现象，即烧结态的多主相（MMP）Nd-La-Ce-Fe-B磁体在25 wt% La-Ce替代Nd时表现出迄今为止报道的最高矫顽力13.0 kOe，结合B-r = 13.12 kG，（BH）（max）= 41.67 MGOe。进一步的退火不能提高矫顽力，而剩磁和能量积急剧降低，即在两步PSA之后为11.0 kOe、12.57 kG和38.71 MGOe，这与常规Nd-Fe-B显著不同。显微组织分析表明，烧结态Nd-La-Ce-Fe-B磁体中REFe 2（Fd（3）over barm）和富RE（Fm（3）over barm）晶间相共存，具有连续的晶界层，隔离相邻的铁磁晶粒。因此PSA对改善合金的微观结构和提高合金的导电性的作用很小。此外，高温PSA破坏了MMP磁体的初始化学不均匀性，导致形成均匀分布的RE晶粒，从而降低了固有磁性能。正如证明了原位洛伦兹TEM表征，PSA样品具有降低的化学梯度表现出快速的畴壁运动，相比之下，在相同的外加磁场下，基本上没有变化的磁畴结构的烧结的。原理验证的微磁模拟进一步证实，保持不均匀的La/Ce/Nd分布是必要的，以抑制磁稀释效应。这些研究结果表明，在MMP磁体中跳过PSA处理不仅可以减少生产工艺和成本，而且可以为设计高性能的基于丰富La/Ce的2：14：1型烧结磁体提供现实的前景。(C)2019 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Two-step post-sinter annealing (PSA) treatment, due to its universal applicability, has been one of the most effective strategies for enhancing the coercivity of Nd-Fe-B sintered magnets. Here we report a peculiar phenomenon that the as-sintered multi-main-phase (MMP) Nd-La-Ce-Fe-B magnet exhibits the highest reported to date coercivity of 13.0 kOe upon 25 wt% La-Ce substituting for Nd, combined with B-r = 13.12 kG, and (BH)(max) = 41.67 MGOe. Further annealing cannot enhance the coercivity whereas the remanence and energy product are drastically lowered, i.e. to 11.0 kOe, 12.57 kG, and 38.71 MGOe after two-step PSA, being remarkably different from the conventional Nd-Fe-B. Microstructural analysis reveals that the as-sintered Nd-La-Ce-Fe-B magnet with coexisting REFe2 (Fd (3) over barm) and RE-rich (Fm (3) over barm) intergranular phases possesses continuous GB layer isolating adjacent ferromagnetic grains. Hence the beneficial role of PSA on modifying the microstructure and strengthening the coercivity is tiny. Additionally, high-temperature PSA destroys the initial chemical heterogeneity of MMP magnets, leading to the formation of REs homogeneously distributed grains and resultant reduction of the intrinsic magnetic properties. As evidenced by in-situ Lorentz TEM characterization, PSA sample with reduced chemical gradient exhibits quick domain wall motion, compared to the as-sintered one with basically unchanged magnetic domain structure upon the same applied field. The proof-of-principle micromagnetic simulation further confirms that retaining the inhomogeneous La/Ce/Nd distribution is essential to suppress the magnetic dilution effect. These findings demonstrate the realistic prospect of skipping PSA treatment in MMP magnets, which can not only reduce the production process and cost, but also delight the scenario for designing high-performance 2:14:1-type sintered magnets based on abundant La/Ce. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.