Effect of grain boundary diffusion of terbium on mode of mechanical fracture of sintered NdFeB magnets

Grain boundary diffusion process (GBDP) is a widely used method of increasing the coercivity of sintered NdFeB magnets. In this study, the effects of the GBDP on the bending strength and microhardness of sintered NdFeB magnets and the fracture mode were investigated. Results show that the bending strength of magnets is reduced by pickling and heat treatment and greatly recovers after heavy rare earth element (Tb) grain boundary diffusion. The pickling and the heat treatment cause a slight decrease in microhardness. Compared with the recovery of the bending strength, the hardness decreases after the GBDP. The fracture mode of bended magnets changes from intergranular to transgranular. This study helps in further improving the mechanical and magnetic properties of sintered NdFeB magnets.