Grain boundary diffusion (GBD) process is an important approach for producing Nd-Fe-B magnets with high coercivity and high thermal stability. The GBD for hot-deformed Nd-Fe-B magnets with nanocrystalline microstructure is more complicated compared to sintered magnets. Here, we investigated the effects of different GBD methods, i.e., intergranular addition (in-situ GBD 1#), in-situ GBD from magnet surface during hot pressing and hot deformation (in-situ GBD 2#), and conventional GBD, on the magnetic properties and microstructure of hot deformed magnets. After the treatment by these three GBD approaches using 2 wt% Pr₄₀Tb₃₀Cu₃₀ diffusion source, the coercivity of the hot-deformed magnet increases from 1281 to 1567, 1412 and 2022 kA/m, respectively. The coercivity enhancement is attributed to the formation of local (Nd,Tb)₂Fe₁₄B phase with strong magnetic anisotropy. Reduced grain orientation is found in both in-situ GBD 1# and conventional GBD treated samples mainly due to the local stress state variation and the rotation of platelet grains. Interestingly, the in-situ GBD 2# processed sample has a high orientation at diffusion surface, which may be caused by the modified surface state of the magnet by the diffusion source. Compared with the in-situ GBD processes, the conventional GBD exhibits a higher utilization efficiency of Tb. Since the in-situ GBD is effective to treat thick hot-deformed magnets, further effort should be aimed at enhancing its diffusion efficiency.

晶界扩散(GBD)工艺是生产具有高矫顽力和高热稳定性的Nd-Fe-B磁体的重要方法。与烧结磁体相比，具有纳米晶微结构的热变形 Nd-Fe-B 磁体的 GBD 更为复杂。在这里，我们研究了不同 GBD 方法的影响，即晶间添加（原位GBD 1#）、热压和热变形过程中磁体表面的原位GBD（原位GBD 2#）和常规 GBD，热变形磁体的磁性能和微观结构。_{在使用 2 wt% Pr 40} Tb ₃₀ Cu ₃₀通过这三种 GBD 方法处理后扩散源，热变形磁体的矫顽力分别从 1281 增加到 1567、1412 和 2022 kA/m。矫顽力的增强归因于具有强磁各向异性的局部(Nd,Tb) ₂ Fe _{14 B相的形成。}在原位GBD 1# 和常规 GBD 处理的样品中都发现晶粒取向减少，这主要是由于局部应力状态变化和片状晶粒的旋转。有趣的是，原位GBD 2#处理的样品在扩散表面具有高取向，这可能是由于扩散源改变了磁体的表面状态造成的。与现场相比GBD 工艺，传统的 GBD 表现出更高的 Tb 利用率。由于原位GBD 可有效处理厚热变形磁体，因此应进一步努力提高其扩散效率。