High-resolution characterization of the internal and external oxidation of austenitic alloys in supercritical water

The surface oxide structures formed on two austenitic alloys after exposure in supercritical water were investigated via high-resolution characterization techniques. Results show that the corrosion processes of 19-Cr and 25-Cr alloys are internal oxidation and external oxidation, respectively. 19-Cr alloy shows a typical duplex thick oxide structure, while 25-Cr alloy has a much thinner protective oxide layer mainly composed of Cr2O3. The higher Cr content of 25-Cr alloy exceeds a critical value that enables the conversion from internal to external oxidation, thus facilitates the formation of a thin continuous Cr2O3 layer and protects the sub-surface from further oxidation. [Display omitted]