Influence of annealing on microstructural and magnetic properties of Nd-Fe-B magnets by grain boundary diffusion with Pr-Cu and Dy-Cu alloys

Abstract The paper presented the effect of post-diffusion annealing on the magnetic properties and microstructure of Nd-Fe-B sintered magnets by grain boundary diffusion with Pr 68 Cu 32 , Dy 70 Cu 30 and Pr 35 Dy 35 Cu 30 alloys. The coercivities of the samples changed slightly by diffusing Pr 68 Cu 32 alloy then increased sharply by subsequent post-diffusion annealing. Differently, the coercivities of the samples showed large rise by diffusing Dy 70 Cu 30 and Pr 35 Dy 35 Cu 30 alloys then slight rise by subsequent annealing. Investigation on microstructure revealed that it was mainly due to different mechanism of grain boundary modification by Pr-Cu and Dy-Cu alloys. The coercivity enhancement of the diffused magnets by Dy 70 Cu 30 and Pr 35 Dy 35 Cu 30 alloys was mainly attributed to continuous Dy-rich shells in extensive layers of Nd 2 Fe 14 B grains. Nevertheless, the coercivity enhancement of the diffused magnets by Pr 68 Cu 32 alloy was mainly resulted from relatively continuous and thin intergranular layers isolating Nd 2 Fe 14 B grains, which were achieved only by post-diffusion annealing.