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

A significant enhancement in coercivity of Nd7.92Pr2.20Fe83.91ZrxB5.57Al0.4−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.