Effect of steam temperature and pressure on the oxidation of potential coating alloy FeCrAl for supercritical water-cooled reactor application

MCrAl (M Fe, Ni, or Co) alloys have exceptional corrosion and oxidation resistance and can be used as both oxidation resistant structural materials and coatings. As coatings, they protect high temperature steels or Ni based alloys by forming a dense alumina layer on the surface and thus impeding further oxidation. In order to assess its potential usage as an overlay coating on components used in supercritical watercooled nuclear reactors (SCWRs), an Fe2 3Cr5Al alloy in the form of wire was tested under two different superheated steam (SHS) conditions (625°C and 800°C) and also in supercritical water (SCW) (625 °C and 26MPa), for 500 h. The corrosion behavior of samples was assessed by measuring the weight change per unit surface area and by examining the surface, crosssectional microstructure and the phase compositions using scanning electron microscopy (SEM) and Xray diffraction (XRD). The tested samples showed different oxidation behavior after exposure to these three conditions. SEM and XRD results showed that FeCrAl has the ability to form protective Al and Crcontaining oxide(s) under all three conditions. Based on the findings, it is concluded that the oxidation behavior of Fe23Cr5Al is highly influenced by pressure and temperature within the range of testing conditions. SHS exposure at low temperature led to greater weight gain while that in SCW resulted in weight loss. Overall, its performance is better under SHS conditions compared to CoCrWC S16 but worse under the SCW condition