高温破碎烧结磁体制取各向异性NdFeB磁粉(Ⅱ)

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

在较高温度下对烧结NdFeB磁体进行机械破碎制取了磁粉.实验结果表明:当破碎温度升高到合金的三元共晶温度附近时,所得磁粉的矫顽力显著高于室温破碎磁粉的矫顽力.高温破碎磁粉矫顽力的升高与磁体破碎时由低温下穿晶断裂向高温下沿晶断裂的转变直接相关.原因在于高温破碎磁粉中,表层穿晶裂纹数量减少,表面较均匀地被富Nd相包覆,以及颗粒中尖锐棱角部位明显减少.高温破碎磁粉的矫顽力经过适当热处理还能进一步提高.

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.