In situ monitoring of stress corrosion at the Alloy 625|NaCl interface

Abstract

Digital holography was used for in situ monitoring of the dynamic stress corrosion processes occurring at the Alloy 625|0.5 M NaCl interface. The introduction of elastic deformation to Alloy 625 through constant extension rate tensile loading increased the anodic and corrosion currents. These increases were attributed to the increased stress caused by elastic deformation, which increased the number of defects in the oxide film on the surface of Alloy 625 and promoted stress corrosion; this was verified by the fact that the accept density (NA) was nearly ten times greater with elastic deformation than without elastic deformation. Intergranular corrosion (IGC) was induced without elastic deformation. IGC induction occurred because chloride ions were readily adsorbed at the grain boundaries and were more active than the grain bodies. However, the application of elastic deformation induced cracks on the alloy surface to enhance stress corrosion, and it inhibited the development of IGC because the cracks were more susceptible to corrosion than the grain boundaries. In-line digital holography revealed that the cracks were initiated in a certain area and progressively advanced to adjacent areas with applied elastic tensile stress.