Effect of (TbF3 + CaH2) pastes grain boundary diffusion on coercivity and remanence of GaAlCu-doped Nd-Fe-B sintered magnets

Grain boundary diffusion of TbF3 can improve the magnetic properties and thermal stability of NdFeB sintered magnets. The reducing agent CaH2 can effectively release reducing gas at high temperature, improve the atmosphere in the furnace. In this paper, the diffusion behavior and coercivity enhancement by printing (TbF3 + CaH2) pastes on the sintered NdFeB magnets was investigated. After diffusion, the coercivity increased rapidly from 15.7 to 28.4 kOe. Tb atoms diffuse first to the surface and then to the interior of the magnet, forming a network of Tb-rich shells around the Nd2Fe14B grains. The higher magnetic crystal anisotropy (Nd,Tb)(2)Fe14B phase determines the coercivity enhancement. This analysis was confirmed by FE-SEM and EDS observations of the microstructure and element distribution of the magnet. In addition, the effect of grain boundary diffusion on the remanence and thermal stability of the magnet was also studied. The results of this study have certain guiding significance for the preparation of sintered NdFeB magnets with high coercivity by diffusion technology.