Inducing and Imaging Localized Passivity Breakdown in Aluminum Using an AFM Approach

Abstract

The impact of localized polarization of aluminum in aqueous chloride is studied using in situ atomic force microscopy (AFM). The primary goal of this study is to determine whether nanostructural degradation in the form of passivity loss and pit initiation can be induced by applying potential pulses between a conductive AFM probe tip and an aluminum surface. Nanoscopic imaging of the mechanically compliant hydrous oxide on an Al(111) textured film with 0.5 wt.% Cu is demonstrated. A correlation is made between characteristic nanostructural changes observed for localized and macroscopic area polarization. Pit initiation proximity to the AFM tip is also demonstrated arguing for millisecond time periods as being sufficient to drive pit initiation within a targeted area. A significant degree of spatial variance in proximity is observed, which suggests a larger length scale, intrinsic susceptibility to pit initiation not dictated by known structural heterogeneity like grain boundary structure.