The substitution of Fe by Co in the 2:14:1 phase is an effective method to increase the Curie temperature and enhance the thermal stability of the Nd-Fe-B magnets. However, the accumulation of Co element at the grain boundaries (GBs) changes the GBs from nonmagnetic to ferromagnetic and causes the thin-layer GBs to become rare. In this paper, the method of diffusing Tb element was chosen to improve the microstructure and temperature stability of high-Co magnets. Three original sintered NdDy-CoFeMB ( = 0, 6 wt%, 12 wt%; M = Cu, Al, Zr) magnets with different Co contents were diffused with Tb by grain boundary diffusion (GBD). After GBD, high-Co magnets exhibit more continuously distributed thin-layer GBs, and their thermal stability is significantly improved. In high-Co magnets ( = 6 wt%), the absolute value of the temperature coefficient of coercivity decreases from 0.603%/K to 0.508%/K in the temperature range of 293–413 K, that of remanence decreases from 0.099%/K to 0.091%/K, and the coercivity increases from 18.44 to 25.04 kOe. Transmission electron microscopy (TEM) characterization reveals that there are both the 1:2 phase and the amorphous phase in the high-Co magnet before and after GBD. EDS elemental analysis shows that Tb element is more likely to preferentially replace the rare earth elements in the 2:14:1 main phase than in the 1:2 phase and the amorphous phase. The concentration of Tb at the edge of the main phase is much higher than that in the 1:2 phase and amorphous phase, which is beneficial to the improvement of the microstructure. The preferential replacement of Tb elements at the edge of the 2:14:1 phase and thin-layer GBs with a more continuous distribution are synergistically responsible for improving the thermal stability of high-Co magnets. The study indicates that GBD is an effective method to improve the microstructure and thermal stability of high-Co magnets.

中文翻译：

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通过铽晶界扩散提高高钴含量 Nd-Fe-B 磁体的热稳定性和微观结构优化


在2:14:1相中用Co替代Fe是提高Nd-Fe-B磁体居里温度、增强热稳定性的有效方法。然而，Co元素在晶界（GB）处的积累使晶界从非磁性变为铁磁性，并导致薄层晶界变得稀少。本文选择扩散Tb元素的方法来改善高Co磁体的微观结构和温度稳定性。三种具有不同 Co 含量的原始烧结 NdDy-CoFeMB（= 0、6 wt%、12 wt%；M = Cu、Al、Zr）磁体通过晶界扩散 (GBD) 扩散 Tb。 GBD之后，高Co磁体表现出更连续分布的薄层GB，并且其热稳定性显着提高。在高Co磁体（=6wt%）中，在293-413K温度范围内，矫顽力温度系数绝对值从0.603%/K降低到0.508%/K，剩磁温度系数绝对值从0.099%/K降低。 K 增加到 0.091%/K，矫顽力从 18.44 kOe 增加到 25.04 kOe。透射电子显微镜（TEM）表征表明，GBD前后的高Co磁体中均存在1:2相和非晶相。 EDS元素分析表明，Tb元素在2:14:1主相中比在1:2相和非晶相中更容易优先取代稀土元素。主相边缘Tb浓度远高于1:2相和非晶相，有利于显微组织的改善。在2:14:1相边缘优先替换Tb元素和具有更连续分布的薄层晶界可以协同提高高Co磁体的热稳定性。 研究表明GBD是改善高Co磁体微观结构和热稳定性的有效方法。