Comparison study on oxidation behavior of advanced nickel- based superalloys in supercritical water (scw)

In this study, we evaluate the oxidation behavior of two nickel based Superalloys including Haynes 230 (Ni-Cr-W-Mo alloy) and Hastelloy N (Ni-Mo-Cr alloy) with a view to its feasible application in the Gen IV supercritical water-cooled reactors. The samples were oxidized in supercritical water with 150 ppb inlet-dissolved O2 at 600 C and 25 MPa. Results show that degradation behavior of these two alloys were different. It was found that Haynes 230 possesses better oxidation resistance in a supercritical environment in comparison with Hastelloy N. The maximum geometric area normalized weight changes for Hastelloy N and Haynes 230 were, respectively, 0.629 and 0.088 mg/cm after 1000 h SCW exposure time. Raman spectra and XRD characterization illustrate the formation of spinel and chromium oxides as the major available phases in the outmost oxide layer in both Superalloys. Surface morphology characterization tests also reveal the effect of exposure time on the surface roughness of oxidized samples. Morphological differences of Hastelloy N and Haynes 230 in different exposure times are also discussed.