回火过程中真空度对烧结NdFeB磁体磁性能的影响

为研究回火过程中真空度对烧结NdFeB磁体显微结构及磁性能的影响，对烧结态磁体采用不同的真空度进行回火。研究发现，高真空回火后，磁体的密度、磁能积和剩磁下降；而采用低真空回火后，磁体的密度、磁能积和剩磁上升，且低真空回火后磁体矫顽力的提高程度要大于高真空回火的磁体。扫描电镜观察发现，与烧结态磁体相比，两种方式的回火后，磁体中的富Nd相均变得更细小，分布更均匀。但高真空回火后磁体中存在着较多且较大的孔洞，薄片状富Nd相挥发后留下的线状晶界缺陷较多；而低真空回火后磁体中的孔洞既少也小，线状晶界缺陷明显较少，且磁体中的富Nd相比高真空回火后的磁体还要细小，分布也更均匀。结果表明，对烧结：NdFeB磁体采用低真空回火可获得较好的磁性能，低真空回火是烧结NdFeB磁体一种较好的回火方式。

Effects of Vacuums on Magnetic Properties of Sintered NdFeB Magnets in Annealing

The as-sintered magnets were annealed in different vacuums, and the effects of vacuums on microstructures and magnetic properties of sintered NdFeB magnets were studied. It was found that after high vacuum annealing, the density, maximum energy product and remanence of magnets become lower. While the corresponding properties of magnets with low vacuum annealing become higher, and the degrees of increase of coercivities are obviously higher than those of magnets with high vacuum annealing. The SEM result showed that compared with the Nd-rich phases of the as-sintered magnets, the Nd-rich phases of the two modes of annealing in magnets are smaller, and distribute more uniformly. However, the magnets of high vacuum annealing have more and bigger pores, and there exist more linear grain boundary defects produced by the volatilization of lamelliform Nd-rich phases. While the pores in the magnets with low vacuum annealing are less and smaller, the linear grain boundary defects are obviously fewer, and the Nd-rich phases are smaller and distribute more uniformly than those of magnets of high vacuum annealing. The results showed that adopting low vacuum annealing can obtain better magnetic properties, and low vacuum annealing is a relatively better mode of annealing for sintered NdFeB magnets.