Microstructure Control and Improvement in Magnetic Properties of Rare-Earth Magnet Powders by Absorption Treatment

钕铁硼磁体是一种典型的稀土磁体，由Nd_2Fe_<14 bbb_0 B相组成，具有较高的磁性。但也存在耐蚀性低、磁性随时间的推移有下降趋势（调味效应）等问题。我们提出了一种新方法。（吸锌）给予高的耐腐蚀性。吸附锌处理还改善了磁性能的时间依赖性。本课题利用透射电子显微镜（TEM）、场发射枪扫描电子显微镜（FE-SEM）和x射线衍射实验（XRD）对hdr - ndfeb磁体粉末及其粘结磁体的微观结构进行了表征。从实验结果中，我们得出以下结论：1。经吸锌处理后，粉末表面和Nd_2Fe_<14>B.2晶界上形成Fe_<11>Zn_<40>相和NdZn_5相。在未进行Zn吸附处理的HDDR-NdFeB中，除h-Nd_2O_3外，在粉末表面和腐蚀处理后的Nd_2Fe_<14>B晶界上还形成α-Fe畴。未经Zn吸附处理的钕铁硼磁性能的调味效应主要是由于α-Fe畴的存在。经zn吸附处理的hdr - ndfeb未形成α-Fe结构域。由于经锌吸收处理后的HDDR-FeNdB中没有a-Fe畴，因此经再磁化后的hdr - fendb具有与原材料一样高的强制功率值。吸锌处理可以提高材料的耐蚀性和磁性能。本研究阐明了这种改善的机制。

NdFeB magnet is a typical rare-earth magnet made of Nd_2Fe_<14>B phase that has a high coersive power. However, it has some problems that it has a low corrosion resistance and a tendency of decreasing in magnetics with time (seasoning effect). We have proposed a new method. (Zn-absorption) to give a high corrosion resistance. It has been found that the Zn-absorption treatment also give an improvement in time-dependence in magnetic properties. In this research project, the microstructures in HDDR-NdFeB magnet powder and bond magnets, made from the powders were characterized by means of transmission electron microscopy (TEM), scanning electron microscopy with a field emission gun (FE-SEM) and x-ray diffraction experiments (XRD). From the experimental results, we drew the conclusions as follows :1.After the Zn-absorption treatment, phases of Fe_<11>Zn_<40> and NdZn_5 are formed on the surface of the powders and on the grain boundaries of Nd_2Fe_<14>B.2.In HDDR-NdFeB without the Zn absorption treatment, α-Fe domains are formed in addition to h-Nd_2O_3 on the surface of the powders and on the grain boundaries of Nd_2Fe_<14>B after corrosion treatment.3.The seasoning effect in magnetic properties of NdFeB without Zn absorption treatment is attributable to the presence of α-Fe domains.4.In HDDR-NdFeB with the Zn-absorption treatment, α-Fe domains are NOT formed.5.Since there are not domains of a-Fe in HDDR-FeNdB with the Zn absorption treatment, it can have the value for coersive power as high as the original one by re-magnetization.6.The Zn absorption treatment can improves the corrosion resistance and the seasoning in magnetic properties. The present study has clarified the mechanism of the improvement.