Analysis of Surface Oxide Films Formed in Hydrogenated Primary Water on Alloy 690TT Samples With Different Surface States

Oxidation of Alloy 690TT samples either manually ground to 400 and 1500 grit, mechanically polished, or electropolished was performed in a solution of 1500 × 10−6 B and 2.3 × 10−6 Li with 2.5 × 10−6 dissolved H2, at 325 °C and 15.6 MPa for 60 days. The oxide films grown on samples with different surface states were analyzed using various techniques. Results show that a triple-layered structure was formed after immersion: an outermost layer with large scattered oxide particles rich in Fe and Ni, an intermediate layer with small compact oxide particles rich in Cr and Fe for the ground surfaces and loose needle-like oxides rich in Ni for the polished surfaces, and an inner layer with continuous Cr-rich oxides. The surface state was found to affect not only the surface morphology, but also the corrosion rate. Grinding accelerated the growth of protective oxide films such that the ground samples showed a lower oxidation rate than the polished ones. Samples of ground Alloy 690TT showed superior resistance to intergranular attack (IGA).