Localized corrosion behavior of scratches on nickel-base Alloy 690TT

Localized corrosion of scratched Alloy 690TT was studied using scanning electrochemical microscopy (SECM) in 10 wt.% NaOH solution and atomic force microscopy (AFM) after short-time oxidation tests in high temperature high pressure water at 250 °C. The results show that the scratches detected by SECM displayed more extensive electrochemical activity. The scratch groove and the whole deformed region caused by scratching as anode corresponded to the peak of tip current. The oxides formed in 250 °C high purity pressurized water nucleated preferentially at the scratch groove and grew faster than non-scratched surface. The nano-grained scratch groove has more electrochemical reactivity than mechanical twins at scratch banks. The intense localized corrosion could contribute to crack initiation at the bottom of scratch groove.