Transmission electron microscopy of oxide development on 9Cr ODS steel in supercritical water

• Published in: Journal of nuclear materials 2009-07, Vol.392 (2), p.280-285
• Main Authors: Siwy, A.D., Clark, T.E., Motta, A.T.
• Format: Article
• Language: English
• Subjects: Applied sciences; Controled nuclear fusion plants; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Fuels; Installations for energy generation and conversion: thermal and electrical energy; Nuclear fuels
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2009.03.032

Oxide layers formed on 9Cr oxide dispersion strengthened ferritic steel alloys during exposure to 600 °C supercritical water for 2- and 4-weeks were examined using cross-sectional transmission electron microscopy. A focused ion beam in situ lift-out technique was used to produce site-specific samples with electron transparent areas up to 8 μm by 10 μm. The oxide layers consist of several sub-layers: an Fe-rich outer oxide, a Cr-rich inner oxide, and a diffusion layer, extending beyond the oxide front into the metal. An evolution of the oxide layer structure is seen between 2 and 4 weeks, resulting in the development of a band of Cr 2O 3 at the diffusion layer/metal interface from the previously existing continuous mixture of FeCr 2O 4 ‘fingers’ and bcc metal. It is believed that transport in this Cr 2O 3 layer at the diffusion layer/metal interface becomes the rate-limiting step for oxide advancement, since this change in oxide structure also corresponds to a decrease in corrosion rate.