Boundary optimization and coercivity enhancement of high (BH)max Nd-Fe-B magnet by diffusing Pr-Tb-Cu-Al alloys

Abstract Commercial N50 Nd-Fe-B magnet was processed by grain boundary diffusing Pr-Tb-Cu-Al alloys. The coercivity increased from original 944.9 kA/m to 1640.6 kA/m, 1741.6 kA/m, 1740.2 kA/m and 1775.4 kA/m by diffusing Tb 70 Cu 30 , Pr 52.5 Tb 17.5 Cu 30 , Pr 60 Tb 20 Al 20 and Pr 60 Tb 10 Cu 15 Al 15 alloys, respectively. Microstructural analysis confirmed Tb-rich shells on the surfaces of Nd 2 Fe 14 B grains, contributing to coercivity enhancement of diffused sample. Especially, the partial replacement of Tb by Pr in diffusion sources resulted in higher coercivity by consuming fewer Tb elements, only 0.34–0.53 wt% Tb in the sample by Pr-Tb-Cu-Al, much lower than 1.82 wt% Tb in the sample by Tb-Cu.