Coercivity and thermal stability enhancement of Nd-Fe-B sintered magnets by grain boundary diffusion with Tb-Al-Cu alloys

The enhancement of the magnetic properties of Nd-Fe-B sintered magnets was investigated using a grain boundary diffusion (GBD) process with serial Tb 80 Al (20-x) Cu x ( x = 5 - 15) (wt.%) alloy diffusion sources to evaluate the influence of non -rare earth metallic elements on the diffusion efficiency. In this study, an optimal Tb diffusion process was achieved at 850 degrees C for 6 h. The coercivity increments ( Delta H c j ) of the GBD-treated magnets were found to vary from 9.7 to 10.3 kOe and the highest value was obtained from a magnet diffused with a Tb 80 Al 5 Cu 15 alloy. The coercivity increments per wt.% Tb usage ( Delta H c j /wt.% Tb) of the alloy-GBD magnets were considerably higher than those of pure Tb-GBD magnets, which revealed a 20 % reduction in Tb usage. The improvement in magnetic thermal stability by Tb 80 (Al-Cu) 20 -GBD was also confirmed.