Recent progress of grain boundary diffusion process of Nd-Fe-B magnets

Energy crisis prompts the society to improve the utilization efficiency of traditional energies and develop new renewable energies. In industrial sector more than half of electric power sources are consumed by various kinds of electric-driven motors. Compared with traditional motors permanent magnet motors exhibit much great advantages in improving the conversion efficiency from the electrical energy to mechanical energy, and vice versa. The fabrication of the permanent magnet motors requires large amounts of permanent magnets. Nd-Fe-B magnets are the most popular permanent magnets in manufacturing permanent magnet motors due to the high magnetic energy product. To keep Nd-Fe-B magnet motors from demagnetizing at high operation temperatures (150 ~ 200 °C) heavy rare earth elements Dy/Tb are added to improve the coercivity. For example, the sintered Nd-Fe-B magnets used for producing wind turbines and electric/hybird vehicle motors usually contain about 10 wt% Dy/Tb. This accelerates the consumption of limited Dy/Tb resources. The technology of grain boundary diffusion process (GBDP) makes full use of Dy/Tb to improve the coercivity of sintered Nd-Fe-B magnets. In addition, GBDP has also been successfully utilized in promoting the coercivity of hot-deformed Nd-Fe-B magnets. This article summarizes the recent developments of GBDP in fabricating Nd-Fe-B magnets with high magnetic properties.