Surface oxidation of Alloy 617 in low oxygen partial pressure He-CO-CO2 environments at 750-850 °C

Surface Cr oxidation mechanism of Alloy 617 was investigated in He-CO-CO2 environments with PCO/PCO2 of either 9 or 1320 at temperatures 750-850 °C. The activation energy for surface oxidation was 169.0 ± 13.2 kJ/mol in He-PCO/PCO2=9 and 234.4 ± 8.9 kJ/mol in He-PCO/PCO2=1320. The ambient oxygen partial pressure dependence of the measured oxidation rates was consistent with n-type behavior of Cr2O3, in which Cr interstitials are the primary mobile species. The oxidation rates measured were greater than that can be sustained only by lattice diffusion of Cr in Cr2O3, indicating that grain boundary diffusion of Cr plays a role in the Cr2O3 growth kinetics.