Influence of dissolved oxygen on oxide films of Alloy 690TT with different surface status in simulated primary water

Oxidation of Alloy 690 with different surface conditions were performed in oxygenated primary water containing B and Li at 325 °C and 15.6 MPa for 2 months. Oxide scales were analyzed using various methods. Results showed triple-layer oxide films were formed: the outmost layer with dispersed big oxide particles; the intermediated layer with loose sheet-like or needle-like oxides and the inner layer with incompact cellular oxides, which were lack of protectiveness. Oxide morphologies were affected by the surface status of samples. Dissolved oxygen increased the intergranular attack (IGA) sensitivity of Alloy 690TT. Growth mechanism of the oxide film was discussed.

► Oxides grown on Alloy 690TT samples in oxygenated primary water were analyzed.
► Triple-layer oxide films on ground and polished samples grown by different mechanisms.
► Loose and Cr depleted oxide films could not protect the matrix from corrosion.
► Morphologies of oxides on Alloy 690TT were related with samples’ surface statuses.
► Alloy 690TT showed higher IGA sensitivity in oxygenated primary water.