Impact of Droplet Wettability on Scanning Electrochemical Cell Microscopy Performance in Stainless Steels

Variations in droplet wettability affect localized corrosion during scanning electrochemical cell microscopy (SECCM) on stainless steel. The droplet dynamics are influenced by stainless-steel microstructural features and surface conditions–such as surface roughness, inclusions, and the addition of an oil layer. As opposed to previous work on aluminum alloys, droplet spreading is promoted by oil immersion, which leads to an increase in the cathodic currents. Rougher surfaces hinder droplet spreading, largely due to the droplet pinning effect, and exhibit higher pitting corrosion incidences compared to smoother surfaces. Moreover, the presence of inclusions intensifies pitting initiation and constrains the landing area (droplet size). We report that while the landing area does not affect the number of metastable pits, small landing areas lead to a high probability of stable pitting.