High resolution analysis of oxidation in Ni-Fe-Cr alloys after exposure to 315 °C deaerated water with added hydrogen

Alloy 600 (Ni-16Cr-9Fe) and Alloy 800 (Fe-35Ni-23Cr) were exposed to simulated primary water at 315 °C. Oxidation phenomena were studied using high resolution electron microscopy. Extensive intergranular oxidation was observed in Alloy 600. In Alloy 800, only shallow intergranular oxygen penetration was detected. The mechanism of intergranular embrittlement in Alloy 600 is likely analogous to internal oxidation. Internal oxidation may not apply to Alloy 800 due to the formation of external rather than internal oxides. Comparisons are made to previous experiments in high temperature hydrogenated steam to validate the latter's use as an accelerated primary water simulant environment.