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 Tb₈₀Al_(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 °C for 6 h. The coercivity increments (ΔH_cj) 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 Tb₈₀Al₅Cu₁₅ alloy. The coercivity increments per wt.% Tb usage (ΔH_cj/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 Tb₈₀(Al-Cu)₂₀-GBD was also confirmed.