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Surface Cr oxidation mechanism of Alloy 617 was investigated in He-CO-CO 2 environments with P CO / P CO 2 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-P CO / P CO 2 = 9 and 234.4 ± 8.9 kJ/mol in He-P CO / P CO 2 = 1320. The ambient oxygen partial pressure dependence of the measured oxidation rates was consistent with n-type behavior of Cr 2 O 3 , 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 Cr 2 O 3 , indicating that grain boundary diffusion of Cr plays a role in the Cr 2 O 3 growth kinetics.

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