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

Based on X-ray diffraction (XRD) patterns, scanning electron microscop y (SEM) investigations, energy dispersive X-ray (EDX) chemical analysi s, thermal analysis (DSC and DTA) and thermomagnetogravimetry (TMG) in vestigations, 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 pow ders, MA leads to an expansion (up to 16 wt.% Si) of the A2 crystallin e 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 temperatu re phases) and stable phases (low temperature phases) was detected. Th e crystalline to amorphous phase transition was a polymorphic phase tr ansition which was attributed to instability of the crystalline lattic e. 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 th e ordering reaction A2-B2 above 16 wt.% Si and the existence of the D0 3 phase at 17 wt.% Si. The influence of the structural state and the g rain size on the magnetic properties such as the coercive force and th e saturation magnetization was also studied. A high coercive force val ue of 17.2x10(3) A m-1 at 1000 Hz frequency and 0.15 T magnetic induct ion was reported for the 5 wt.% Si composition sample. An increase in ductility and low hysteresis loop were observed for the 10 wt.% Si com position.