Abstract In this article, evaluations of the microstructure and HRE distribution of grain boundary diffused (GBD) Nd-Fe-B sintered magnets with diffusion time (t) and diffusion depth (d) were investigated. The coercivity (Hcj) first increases and then decreases with increasing t; while the remanence (Br) and the maximun energy product ((BH)m) of GBD magnets have an opposite changing trend. A large amount of Tb diffused into the inner of grains, and formed extensive Tb-rich areas in the surface layer at the beginning of GBD process. This suggests that Tb diffuses not only along grain boundaries, but also via grains in the surface layer because of high concentration gradient of Tb. As the concentration gradient of Tb is reduced, Tb diffuses mainly along grain boundaries. The grain boundary acts as the GBD path, but not as a Tb enriched area. There are two coexisting processes, namely, one process is diffusing from the surface to the inside of the magnet, the other is diffusing from the grain boundaries to the shell, then to the inner of grains. The two diffusion processes cause the changes of microstructure and Tb distribution, thus, the magnetic properties of the GBD samples vary correspondingly.

中文翻译：

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TbHx 扩散处理 Nd-Fe-B 烧结磁体中微观结构和磁性随扩散时间的演变

摘要 在本文中，研究了晶界扩散 (GBD) Nd-Fe-B 烧结磁体的微观结构和 HRE 分布随扩散时间 (t) 和扩散深度 (d) 的评估。矫顽力（Hcj）随着t的增大先增大后减小；而GBD磁体的剩磁（Br）和最大能积（（BH）m）则有相反的变化趋势。GBD过程开始时，大量的Tb扩散到晶粒内部，并在表层形成了广泛的富Tb区。这表明 Tb 不仅沿晶界扩散，而且由于 Tb 的高浓度梯度，还通过表面层中的晶粒扩散。随着 Tb 浓度梯度的减小，Tb 主要沿晶界扩散。晶界充当 GBD 路径，但不是 Tb 富集区。有两种并存的过程，即一种是从磁体表面向内部扩散，另一种是从晶界向壳层扩散，然后向晶粒内部扩散。这两种扩散过程引起微观结构和Tb分布的变化，因此GBD样品的磁性能相应变化。