Effective microstructure optimization and coercivity enhancement of sintered Nd–Fe–B magnet by grain boundary diffusion of Pr60Tb13Al27 alloy

Commercial sintered Nd-Fe-B magnet was grain boundary diffusion (GBD) processed by Pr60Tb13Al27 and Tb73Al27 alloys. Although the Tb content is only 13 at% in the Pr60Tb13Al27 alloy, the coercivity was significantly enhanced from 15.18 kOe to 26.30 kOe in the magnet diffused by Pr60Tb13Al27, higher than 24.08 kOe of the Tb73Al27 GBD magnet. This suggests that the substitution of Tb(60 at%) by Pr in the Tb73Al27 alloy can further enhance coercivity. Detailed microstructure analysis showed that, in the Pr60Tb13Al27 GBD magnet, the Tb-rich shell thickness was reduced and the two-layer Tb-rich shell was formed. Furthermore, a large number of continuous grain boundary phases was observed, which significantly enhances the exchange-decoupling effect between adjacent grains. The effect of Pr for the Tb-rich shell and grain boundary structure was discussed based on the experimental results.