Experimental study of the bcc-fcc phase transformations in the Fe-rich system Fe-Si at high pressures

摘要

In situ X-ray diffraction experiments at high pressure were carried out up to 8.9 GPa and 1100 deg C to study phase transformations of iron and two iron-silicon alloys Fe_(0.91)Si_(0.09) and Fe_(0.83)Si_(0.17). For iron, the transformation from the bcc phase to the fcc phase was observed at pressures 3.8-8.2 GPa and temperatures that are consistent with previous in situ X-ray diffraction studies. reversal of the transformation of iron was found to be sensitive to temperature; hysteresis of the transformation increased from 25 deg C at 3.8 GPa to 100 deg C at 7.0 GPa, primarily because the bcc-fcc phase boundary has a negative Clayperon slope. In the binary system Fe-Si, the observations of the present study indicate that the ferrite (bcc phase)-stabilizing behavior of silicon persists at high pressures and that the maximum solubility of silicon in the fcc phase increases with increasing pressure: (1) the transformation from the bcc phase to the fcc phase was observed in Fe_(0.91)Si_(0.09) at 6.0, 7.4 and 8.9 GPa and the temperatures measured at the onset of the transformations were 300 deg C higher than those in iron at similar pressures, (2) the transformation rate in Fe_(0.91)Si_(0.09) was extremely sluggish compared to that of iron, and (3) the bcc-fcc phase transformation was not observed in Fe_(0.91)Si_(0.09) at 4.7 GPa up to 1000 deg C and in Fe_(0.83)Si_(0.17) at 8.2 GPa and 1100 deg C.