Microstructure evolution and coercivity enhancment of sintered Nd–Fe–B magnets by grain boundary diffusion with Cu aided TbF3

Abstract

Abstract Compared with the TbF3 grain boundary diffusion (GBD) magnet, in this study, Cu aided TbF3 GBD was applied to Nd-Fe-B magnets to further improve the coercivity. It is found that the coercivity increased sharply from 17.42 kOe to 25.43 kOe when the diffusion source is the mix powders of Cu and TbF3, higher than 21.25 kOe with single TbF3 as the diffusion source. The wettability of the grain boundary phases were improved owing to the accumulation of Cu in grain boundary. The grains were uniformly enveloped by grain boundary phase with the help of Cu addition. The microstructure analysis indicated that the diffusion depth of Tb increased significantly due to the modified grain boundaries which offered better tunnels for the diffusion of Tb.