氧含量对烧结钕铁硼磁体Dy晶界扩散的影响研究

Influence of Oxygen content on Dy grain boundary diffusion in Nd-Fe-B sintered magnets

摘要:

本文主要研究了烧结钕铁硼磁体中氧含量变化对Dy晶界扩散后的Dy含量及矫顽力增加量的影响。选取多种高、低氧磁体进行Dy扩散处理后比较发现,低氧磁体的Dy扩散量和矫顽力提高量均明显高于高氧磁体。对9个0wt.%Dy的不同氧含量样品进行扩散再次确认,氧含量减少有利于Dy扩散量、矫顽力的提高。各样品成分梯度结果显示,低氧磁体的Dy扩散量由表及里全面高于高氧磁体,内外浓度梯度也小于后者。电子探针表征结果表明,低氧磁体Dy扩散后晶界处Dy富集条纹更明显、连续,完整包裹各个主相晶粒。这种结构优化也使低氧磁体各向异性场提高幅度大于高氧磁体。磁体中氧含量降低使富钕相在主相周边均匀连续分布,为后续进入磁体内部的Dy元素提供连续的扩散通道,从而使磁体的Dy扩散量和矫顽力提高量进一步提高。

Abstract:

In present work, the influence of the oxygen content variation on the Dy increment and the coercivity increment in Dy grain boundary diffusion processed (GBDP) Nd-Fe-B sintered magnet was investigated. Various magnets including both high and low oxygen types were processed and the latter one showed higher increments either in Dy contents or in Hcj. Nine specimens with 0wt. % original Dy contents were compared after GBDP, and it was proved that decrease of oxygen is beneficial to Dy content and Hcj increase. Furthermore, Dy content gradient in each GBDP sample showed that the gap between the outer and interior region in low oxygen magnets were narrower. According to the EPMA figures, Dy-rich shells were more continuous and brighter and almost completely surrounded each matrix grains in low oxygen GBDP magnet. The optimization of the microstructure enabled the low oxygen GBDP sample to gain a higher anisotropic field increment. Decrease of oxygen lead to Nd-rich phase surround the matrix phase more homogeneously and continuously, providing a more continuous tunnel for Dy to diffuse into the magnet, ultimately inducing a further enhancements of Dy content and Hcj.