Nd56Fe30Al10Dy4大块非晶合金晶化过程中磁性及微观结构的研究

采用铜模吸铸法制备Nd56Fe30Al10Dy4大块非晶合金,利用差示扫描量热仪(DSC)、振动样品磁强计(VSM)、X射线衍射仪(XRD)和扫描电镜(SEM)研究了该合金晶化过程中磁性及微观结构的变化。结果表明,铸态下合金表现为明显的硬磁性,在765 K退火后,合金中有少量晶态相产生,内禀矫顽力和饱和磁化强度略有下降。随着退火温度升高,合金中晶态相的相对含量逐渐增加,非晶相的相对含量逐渐减少,饱和磁化强度逐渐降低,但其内禀矫顽力变化不大。810 K退火后,合金完全晶化,铁磁性消失。结合合金的磁性能、微观结构、铁磁交换耦合作用的结果分析,Nd基大块非晶合金的矫顽力来源于合金中非晶相,但非晶相的相对含量却对矫顽力影响不大,这可以用强钉扎机制进行解释。

Magnetic Properties and Microstructure of Nd56Fe30Al10Dy4 Bulk Amorphous Alloy during Crystallization Process

Nd56Fe30Al10Dy4 bulk amorphous alloy was prepared by copper mould casting. The magnetic properties and microstructure of the alloy during crystallization process were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and scanning electron microscope (SEM). Results indicate that the as-cast alloy exhibits hard magnetic behavior. A few crystalline phases are observed and the intrinsic coercivity and saturation magnetization of the alloy decrease slightly after annealing at 765 K. With increasing the annealing temperature, the volume fractions of crystalline phase increase and the volume fractions of amorphous phase decrease gradually in the alloy, while the saturation magnetization of the alloy decrease gradually. It is worthy of noting that intrinsic coercivity changes slightly with increasing the annealing temperature. After annealing at 810 K, the alloy shows paramagnetic behavior while no amorphous alloy is observed. Based on the results of magnetic properties, microstructure and exchange-coupling interaction, it is found that coercivity of the alloy is derived from amorphous phase while it does not depend on the volume fraction. The mechanism responsible for coercivity in Nd-based bulk amorphous alloys could be explained by a strong pinning model