Time-resolved X-ray diffraction study on solidification of Fe-B and Fe-C eutectic alloys

摘要

Solidification processes of Fe-B and Fe-C eutectic alloys have been investigated by a time-resolved synchrotron x-ray diffraction under containerless cooling conditions using a conical nozzle levitation technique. To observe relative variations of structure from the undercooled liquid to crystalline phase, we have conducted millisecond order time-resolved x-ray diffraction experiments with a two-dimensional detector. The structural variations observed during the solidification of the Fe_(83)C_(17) alloy were identified as the phase transformation process expected from the Fe-C phase diagram. As for the Fe_(83)C_(17) alloy, it was revealed that a metastable phase composed of Fe_(23)B_6 compound was precipitated as a primary crystalline phase from the undercooled liquid. In addition, decomposition of the metastable Fe_(23)B_6 phase showed dependence on the cooling rate of the sample. At the cooling rate of 30 K/s, the Fe_(23)B_6 phase decomposed to bcc-Fe and FeiB phases with decreasing temperature. On the contrary, at the cooling rate of 180 KVs, the metastable Fe_(23)B_6 phase remained in spite of an appearance of the bcc-Fe phase. By comparing the primary crystalline phase between the Fe_(83)C_(17) and the Fe_(83)C_(17) alloys, we suggest that the formability of the metastable Cr_(23)C_6-type compound is closely related with the glass-forming ability of Fe-metalloid binary alloys.