Oxidation behaviour of alloy S16 in superheated steam and supercritical water

The performance of S16, a CoCrWC alloy, was evaluated in superheated steam (SHS) at 625°C and 800°C (at 0.1 MPa), and in supercritical water (SCW) at 625°C and 26 MPa for 500 hours. S16 experienced weight loss under the SHS conditions (625°C and 800°C) and weight gain under the SCW condition. Weight loss was associated with scale spallation and pitting while oxide growth on the surface contributed to weight gain. Formation of CoCr2O4 and Cr2O3 was observed in the oxide layer of samples tested under the three conditions, however, the Cr-rich oxide on SCW tested samples was found to be continuous. A thin, continuous Co3W subscale was believed to have provided an oxidation barrier under the SCW test condition. Based on the limited weight change and surface oxide formation, S16 has the potential to be used as a coating material for ultra-supercritical power generation systems at temperatures up to 625°C