Time-Resolved Observation of Phase Transformation in FeC System during Cooling via X-ray Absorption Spectroscopy.

The kinetics of phase transformation in the FeC system during cooling are of great importance for controlling its microstructure and mechanical properties. However, real-time observation of the phase transformation has been a challenging task because of experimental difficulties. Here, we developed an analytical technique for time-resolved observation of the phase transformation of an FeC system during cooling via X-ray absorption spectroscopy with a time resolution of 200 µs. The technique was applied to model specimens: Fe, Fe0.044C, and Fe1.24C. The incubation time before phase transformation and the multiple steps of phase transformation from £-Fe to ¡-Fe (+ Fe3C) could be clearly observed by the proposed technique, and the behaviors were significantly different among the specimens. Through the developed technique, change in atomic structures at a short-range scale was detected, which is complementary to X-ray diffraction that detects atomic structures only in long-range order. The developed technique can detect structure changes at early stage of phase transformations, where structures changes often begin at a short-range scale, and provide inevitable information on the kinetics. [ABSTRACT FROM AUTHOR]