Mechanical polishing, surface roughness, near‐surface deformation, and electrochemical corrosion of Alloy 690TT

Abstract

The effects of mechanical grinding/polishing, surface roughness, and near‐surface deformation on the electrochemical corrosion behavior of thermally treated (TT) Alloy 690 were studied in a sodium chloride solution. The X‐ray photoelectron spectroscopy and transmission electron microscopy analyses revealed that mechanical grinding/polishing can change the ratio of the elements at the surface of the as‐received Alloy 690TT specimen by removing its Cr‐rich outer layer and causing deformation at the near‐surface microstructure, something which has a direct impact on the rate of the oxygen reduction reaction (ORR), the pitting potential (Epit), and the corrosion potential (Ecorr) of Alloy 690TT. It was observed that the ratio of Cr in the surface is a significant factor that controls the rate of the ORR and the corrosion parameters such as Ecorr. Higher amounts of Cr at the surface accelerate the ORR. The near‐surface deformation shifts the Epit values towards less positive potentials. It was also found that due to the different near‐surface chemical composition of the as‐received Alloy 690TT specimen compared with the ground and the polished specimens, the surface roughness parameters do not have a regular correlation with the rate of the ORR and the values of the Ecorr and the Epit. Only the passive current density increases when the surface roughness is increased. Copyright © 2015 John Wiley & Sons, Ltd.