Passivation of Ni-Cr and Ni-Cr-Mo Alloys in Low and High pH Sulfate Solutions

The kinetics of passive oxide film formation, its thickening, and composition on Ni-22Cr Ni-22Cr-6Mo wt% alloys were investigated at selected anodic potentials. Experiments performed in acidic alkaline sulfate environments using a number characterization techniques including combination potentiodynamic polarization, on-line atomic emission spectro-electrochemistry (AESEC), situ potentiostatic growth, along with neutron reflectometry (NR) ex X-ray photoelectron spectroscopy (XPS). roles solution pH Mo the passivation behavior discussed terms thermodynamic kinetic factors governing passivation. was found to have an impact relative chemical compositions alloy but not noticeably for alloy. Ni-rich films formed early during process while Cr(III) enrichment observed longer times, albeit less extensively than previously Cl − solutions. fraction cations also increased alloying low high demonstrating strong effect content aqueous Ni based superalloys, however, larger is seen . This noteworthy finding as usually assumed mainly influence pit crevice stabilization.