Observation of high-temperature phase transformation in the aluminide Cr–Mo steel using EBSD

Abstract

5Cr–0.5Mo steel was coated by hot-dipping into a molten aluminum bath. The phase transformation in the aluminide layer during diffusion at 750 °C in static air was analyzed by Electron Backscatter Diffraction (EBSD). The results showed that the aluminide layer of the as-coated specimen consisted of an outer FeAl 3 layer and an inner Fe 2Al 5 layer. The Fe 2Al 5 phase kept growing with increasing exposure time at 750 °C, while the FeAl 3 phase remained constant. The FeAl 3 phase disappeared as the aluminum layer was consumed. After 60 min of exposure, FeAl 2 phase formed at the inner and outer sides of the Fe 2Al 5 phase, while FeAl phase formed at the interface between FeAl 2 and the steel substrate. With prolonged exposure, the thickness of FeAl increased and the volume of FeAl 2 expanded at the expense of Fe 2Al 5. Crystal Orientation Map (COM) revealed that Fe 2Al 5 grew preferentially along the C-axis, [001] direction, of the crystal structure.