Effect of DyF3 and TbF3 Additions on the Coercivity Enhancement in Grain Boundary Diffusion Processed Nd-Fe-B Permanent Magnets

摘要

The coercivity of Nd-Fe-B magnets can be improved by Dy or Tb additions to substitute Nd. In this study, the Nd-Fe-B permanent magnets were simple dip-coated in ethanol based DyF3 and TbF3. Then they were heat treated to permit Dy or Tb diffuses into the Nd-Fe-B magnet grain boundary. We investigated effect of DyF3 and TbF3 additions on the coercivity enhancement in grain boundary diffusion process (GBDP) of Nd-Fe-B permanent magnets. The GBDP at temperatures of 800, 850, 900, 950, 1000, and 1050°C were investigated. As a result, the coercivity of permanent magnets increased by both DyF3 and TbF3 additions, while there is no significant affect to remanence. The optimum coercivity was achieved after the GBDP at 900°C for 2 hours and subsequently tempered at 500°C for 2 hours. The coercivity after GBDP with DyF3 addition is 1.58 times higher than initial magnet, while with TbF3 addition is 1.76 times higher than initial magnet.