Preparation of Anisotropic NdFeB Powders by Crushing Sintered Magnet at High Temperatures (Ⅱ)

Anisotropic NdFeB magnet powders were prepared by crushing a sintered magnet at elevated temperatures. The experimental results show that the coercivity of the magnet powders prepared at higher crush temperatures near or above the ternary eutectic temperature of the NdFeB magnetic alloy, can reach a much higher value than that obtained by room-temperature crush. The influence of crush temperature on coercivity is closely related to the transition of the fracture way from transgranlar to intergranular manner with increasing crush temperature. In a crush process at an elevated temperature, the reduction of cracks in the surface layer and of sharp edges and corners of the magnet powders, and the formation of an Nd-rich phase thin layer more homogeneously distributed on the powder surface should be the reason for the increase in coercivity. The experiments also show that a following annealing treatment of the obtained powders can further improve the coercivity.