NdFeB 磁体的Dy 热扩渗过程及其矫顽力提高机制

Abstract

Thermal diffusion of heavy rare earths is an important technology for preparation of the sintering NdFeB magnets with high-performance and low-cost. However, the stability of diffusing process is lower and the mechanism of Dy diffusion is still unclear, which has become a bottleneck affecting the large-scale application of the technology. In this work, commercial 35M magnets prepared with recycled materials was used as original magnets. A novel home-made DyF3 coating, which can prepare uniform and adhesive Dy coating layer on the surface of the NdFeB magnet, was employed into Dy diffusion treatment. The results show that the DyF3 coating has advantages of quick-drying, good adhesion and uniform coating, which effectively improved the stability of thermal diffusion process. An optimal Dy diffusion process was obtained when the thermal diffusion was conducted at 900С for 10 h. The coercivity of the magnet obtained by the optimal process reached to 1710.2 kA/m, increased by 37.9%, with a negligible decrease of remanence. The analysis of microstructure indicates that during the thermal diffusion, Dy element diffused along the grain boundary into the magnet and a Dy-rich shell layer (Nd, Dy)2Fe14B was formed around the main crystal phase. The mechanism of coercivity improvement of the magnets were discussed. Higher magnetic anisotropy field Dy-rich shell layer and the continuous and clear Nd-rich phase at the grain boundary resulted in a significant increase in the coercivity of the magnets