Nd-Fe-B hot-pressed (HP) magnet prepared from melt-spun MQU-F flakes features coarse grains (CG) with the average size of both 200 nm (CG_S) and 700 nm (CG_L) at flake boundary. The grain growth at the flake boundary of Nd₂Fe₁₄B/α-Fe composite HP magnet before and after diffusion of low-melting-point Pr₈₂Cu₁₈ phase was investigated, revealing the indispensable role of surface RE-rich phase of melt-spun flakes in the formation of CG in HP magnet. The dominant role of surface oxygen content of melt-spun flakes in the formation of CG_L has been clarified with etching method. The HP magnet prepared from the etched flakes with dramatically decreased oxygen content exhibits the CG regions merely with homogeneous equiaxed CG_S at flake boundary. Consequently, the coercivity (μ₀H_c) shows significant increase while remanent magnetization (μ₀M_r) inappreciable change. Further investigation with sieving method reveals the elimination of CG_L via removal of the fine Nd-Fe-B flakes smaller than 54 μm due to their much higher oxygen content, confirming the dominant role of oxygen content in the formation of CG_L. The quantitative analysis on the magnetic properties of the above HP magnets reveals the monotonic increase of coercivity (μ₀H_c) and negligible change of remanent magnetization (μ₀M_r) with decreased oxygen contents of Nd-Fe-B flakes. The maximum value of coercivity (μ₀H_c) increases from 2.26 to 2.47 T as the oxygen content decreases from 0.1692 wt% to 0.079 wt%.

由熔纺 MQU-F 薄片制备的 Nd-Fe-B 热压 (HP) 磁体具有粗晶粒 (CG )，薄片边界处的平均尺寸为 200 nm (CG _S ) 和 700 nm (CG _L )。研究了低熔点 Pr ₈₂ Cu ₁₈相扩散前后Nd ₂ Fe ₁₄ B/α-Fe 复合 HP 磁体片状边界的晶粒长大，揭示了熔体表面富 RE 相不可或缺的作用- 在 HP 磁铁中形成 CG 的纺丝薄片。熔纺薄片表面氧含量在CG _L形成中的主导作用已用蚀刻法澄清。由氧含量显着降低的蚀刻薄片制备的 HP 磁体在薄片边界处仅具有均匀的等轴 CG _S区域。因此，矫顽力 ( μ ₀ H _c ) 显示出显着增加，而剩磁 ( μ ₀ M _r ) 变化不大。用筛分法进一步研究表明，通过去除小于 54 μm 的细 Nd-Fe-B 薄片，由于它们的氧含量高得多，从而消除了 CG _L，证实了氧含量在 CG _L形成中的主导作用. 对上述HP磁体磁性能的定量分析表明，随着Nd-Fe-B薄片氧含量的降低，矫顽力（μ ₀ H _c）单调增加，剩磁强度（μ ₀ M _r）变化可忽略不计。随着氧含量从 0.1692 wt% 减少到 0.079 wt% ，矫顽力的最大值 ( μ ₀ H _c ) 从 2.26 T 增加到 2.47 T。