Electrochemical Corrosion Performance of Mechanically Polished Alloy 690TT at High-Temperature Water (200°C)

The electrochemical corrosion performance of thermally treated (TT) Alloy 690 (UNS N06690) was investigated in 200°C pressurized water before and after mechanical polishing/grinding. The surface analysis of the specimens was performed using atomic force microscopy, x-ray photoelectron spectroscopy, transmission electron microscopy coupled with energy dispersive spectroscopy, and focused ion beam microscopy. A Cr-rich outer layer formed during the TT process was detected at the surface of the as-received Alloy 690TT specimens. As a result of the greater formation of the Cr-based oxide film, the as-received specimen showed a more desirable corrosion behavior in both oxygenated and deoxygenated water environments. The near-surface microstructure of the as-received specimen was changed by mechanical polishing/grinding of the surface. The ground specimen showed a higher degree of deformation/dislocation than the polished specimen.