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 Tb70Cu30, Pr52.5Tb17.5Cu30, Pr60Tb20Al20 and Pr60Tb10Cu15Al15 alloys, respectively. Microstructural analysis confirmed Tb-rich shells on the surfaces of Nd2Fe14B 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.