Coercivity enhancement in Nd-Fe-B magnetic powders by Nd-Cu-Al grain boundary diffusion

Highlights: • Coercivity of melt-spun Nd-Fe-B magnetic powders is enhanced by the diffusion treatment of NdCuAl alloy. • The diffusion-processed magnetic powders shows the highest coercivity of 23.14 kOe at room temperature. • At 175 °C, the diffusion-treated Nd-Fe-B bonded magnets possess the highest coercivity of 9.8 kOe. • The thermal-stability of bonded magnets is significantly improved after the diffusion process. A significant enhancement in coercivity of Nd_7.92Pr_2.20Fe_83.91Zr_xB_5.57Al_0.4−x powders was achieved by Nd₈₀Cu₁₀Al₁₀ grain boundary diffusion. The room temperature coercivity was drastically increased from 7.4 kOe to 23.14 kOe by the diffusion process with the content 30% of Nd₈₀Cu₁₀Al₁₀ alloy. Nd-Cu-Al alloy diffusion process resulted in grain growth and formed continuous grain boundary phases. The boundary layers were very effective in pinning the motion of domain walls, leading to an increased coercivity. In addition, an increased coercivity was also obtained from 3.1 kOe to 9.8 kOe at 175 °C in the bonded magnets with the diffusion of 30% content NdCuAl alloy. So the thermal stability of the bonded magnets was improved.