Corrosion properties of steel protected by nanometre-thick oxide coatings

A comprehensive study of the corrosion properties of low alloy steel protected by 40-50 nm aluminium and tantalum mixed oxide coatings grown by atomic layer deposition is reported. Electrochemical and surface analysis was performed to address the effect of substrate surface finish and whether an oxide mixture or nanolaminate was used. There was no dissolution or breakdown for nanolaminate alumina/tantala stacks in acidic NaCl solution. Localised corrosion (pitting) took place when defects exposing the substrate pre-existed in the coating. Substrate pre-treatment by brushing and H2-Ar plasma was instrumental to block or slow down pit initiation by reducing the defect dimensions.