Amorphous Fe-C-Si alloys
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netization, Curie temperature, coercive field, and permeability were measured using a magnetic balance, a B-H tracer, and an impedance analyzer. The crystallization behavior of the alloys was examined at a heating rate of 40 K/s by a differential scanning calorimetry (DSC). Figure 1 shows the composition range in which an amorphous phase is formed without any trace of crystallinity for the Fe-C-Si alloy system, along with the data 13 of equilibrium Solidus phase fields at 1273 K. The amorphous alloy formation field extends in a range above about 9 at. pct C and about 4 at. pct Si, with the total metalloid content more than about 30 at. pct. As an example, a TEM micrograph and a selected area diffraction pattern taken from an electrolytically-thinned FeToC20Sil0 amorphous alloy are shown in Figure 2, together with the X-ray diffraction pattern of the same alloy without thinning treatment. Lack of contrast in the bright-field image (a) and two broad diffuse haloes in the electron and X-ray diffraction patterns (b and c) indicate clearly the formation of a homogeneously amorphous phase. Lack of information on alloys having higher metalloid concentrations in the amorphous field of Figure 1 is due to increase in the difficulty of sample preparation, resulting from a rapid rise of melting temperature with increasing C and Si contents. The minimum metalloid concentration required for the formation of amorphous Fe-C-Si alloys is considerably higher than the metalloid concentrations for Fe-C-P amorphous alloys (17 to 27 at. pct 14)and for Fe-C-B amorphous alloys (10 to 25 at. pct14). Such a marked difference in metalloid concentrations between FeC-Si and Fe-C-(P or B) amorphous alloys allows the following inferences: (1) the effect of Si on the enhancement of glass-forming ability of Fe-C alloys is much smaller than that of P and B, and (2) an interaction among the constituent atoms in the molten alloy (required for glass formation) is significantly different between the alloy systems discussed. Figure 1 also shows that the amorphous formation region lies in the equilibrium phase fields of ferrite + graphite, 30
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