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

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 FeAl3 layer and an inner Fe2Al5 layer. The Fe2Al5 phase kept growing with increasing exposure time at 750 °C, while the FeAl3 phase remained constant. The FeAl3 phase disappeared as the aluminum layer was consumed. After 60 min of exposure, FeAl2 phase formed at the inner and outer sides of the Fe2Al5 phase, while FeAl phase formed at the interface between FeAl2 and the steel substrate. With prolonged exposure, the thickness of FeAl increased and the volume of FeAl2 expanded at the expense of Fe2Al5. Crystal Orientation Map (COM) revealed that Fe2Al5 grew preferentially along the C-axis, [001] direction, of the crystal structure.