Abstract Dy distributions in Dy-free and Dy-containing Nd Fe B sintered magnets in the course of the Dy-vapor grain boundary diffusion (GBD) process have been investigated in order to understand the origin of the high coercivity of 3.0 T that is reachable only when the initial magnet is alloyed with Dy. We have discovered the formation of a secondary Dy-rich shell within the well-known primary Dy-rich shell, which is a key contributor to the 3.0 T coercivity. The coercivity increment of the Dy-containing magnet after the GBD treatment was only 0.08 T, much lower than 0.87 T for the Dy-free magnet; however, it was substantially enhanced by a post-diffusion annealing. Compared to the Dy-free magnet, a larger amount of Dy atoms were diffused from the Nd-rich grain boundary (GB) phase to the primary Dy-rich shell in the Dy-containing magnet after the annealing, resulting in the formation of a secondary Dy-rich shell with a higher Dy-concentration at the GB phase/secondary shell interfaces.

中文翻译：

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晶界扩散加工的无镝和含镝钕铁硼烧结磁体的显微组织和矫顽力

摘要 为了了解可达到的 3.0 T 高矫顽力的起源，研究了在 Dy 蒸气晶界扩散 (GBD) 过程中无 Dy 和含 Dy 的 Nd Fe B 烧结磁体中的 Dy 分布仅当初始磁铁与 Dy 形成合金时。我们发现在众所周知的初级富 Dy 壳中形成了次级富 Dy 壳，这是 3.0 T 矫顽力的关键因素。GBD处理后含Dy磁体的矫顽力增量仅为0.08T，远低于无Dy磁体的0.87T；然而，它通过后扩散退火得到了显着增强。与无镝磁铁相比，