MECHANISM OF MECHANICAL ALLOYING PHASE-FORMATION AND RELATED MAGNETIC AND MECHANICAL-PROPERTIES IN THE FE-SI SYSTEM

Based on X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) investigations, energy dispersive X-ray (EDX) chemical analysis, thermal analysis (DSC and DTA) and thermomagnetogravimetry (TMG) investigations, the far from equilibrium crystalline to amorphous phase transition induced by mechanical alloying (MA) in the Fe-rich side of the Fe-Si system was studied. Starting from a mixture of Fe and Si powders, MA leads to an expansion (up to 16 wt.% Si) of the A2 crystalline disordered solid solution phase domain. In this composition field an amorphous phase is also detected. For an Si content larger than 16 wt.% Si, a mixture of metastable phases (an amorphous and high temperature phases) and stable phases (low temperature phases) was detected. The crystalline to amorphous phase transition was a polymorphic phase transition which was attributed to instability of the crystalline lattice. The expansion of the A2 phase domain up to 15 wt.% Si was confirmed by Vicker's microhardness measurements, as well as the starting of the ordering reaction A2-B2 above 16 wt.% Si and the existence of the D03 phase at 17 wt.% Si. The influence of the structural state and the grain size on the magnetic properties such as the coercive force and the saturation magnetization was also studied. A high coercive force value of 17.2x10(3) A m-1 at 1000 Hz frequency and 0.15 T magnetic induction was reported for the 5 wt.% Si composition sample. An increase in ductility and low hysteresis loop were observed for the 10 wt.% Si composition.