Towards Quantitative Microscale Corrosion Analysis: Size-Dependent Inclusion-Assisted Pitting Susceptibility Studied by Scanning Electrochemical Cell Microscopy–Chronoamperometry

Scanning electrochemical cell microscopy (SECCM) was employed to systematically investigate inclusion-induced localized corrosion with statistically meaningful spatial sampling. Using stainless steel 316-L (SS 316-L) as a model material, SECCM measurements were performed over both passive matrix regions and MnS inclusions, as identified by post-measurement microscopy. Analysis of potentiodynamic polarization curves acquired at inclusion sites with Tafel analysis yielded inconsistent results, highlighting limitations of conventional macroscale methods applied at the microscale for the passive system. Instead, a distinct breakdown potential feature, observed exclusively at inclusion sites, proved to be a more informative parameter extracted from the polarization data. To evaluate the stability of localized anodic activity at varying sizes of inclusions (~0.2 – 3 µm 2 ), chronoamperometric measurements were conducted. The magnitude of anodic currents was directly correlated to the probed inclusion areas (areas of inclusions or inclusion parts enclosed in an SECCM footprint), showing a linear direct relationship. This study provides statistically grounded new insight into how inclusion size governs the persistence of localized anodic activity of passive metals, advancing prior macroscale observations and limited single-inclusion analyses into a robust microscale understanding. Furthermore, the presented SECCM – chronoamperometry workflow enabled high-resolution electrochemical investigations without limitations of Tafel theory at the microscale and could potentially be extended to study other passive materials with high inclusion densities.