This article investigates the modification of a carbon steel surface by benzotriazole (BTA), and the structure and properties of the formed layers. Adsorption was studied by surface analytical methods such as X-ray photoelectron spectroscopy (XPS) and reflecting infrared microscopy (FTIR). It has been established that a polymer-like film containing iron-azole complexes that are 2 nm thick and strongly bonded to the metal is formed on the surface as a result of the azole interacting with a steel surface. This film is capable to inhibit uniform and localized corrosion of steel in neutral aqueous electrolytes containing chloride ions. It is shown that the iron-azole layer located at the interface acts as a promotor of adhesion, increasing the interaction of polymeric coatings with the steel surface. Taking into account these properties, the steel pretreatments can be used for improving the anticorrosion properties of polymeric coatings applied for the protection of steel constructions.

The interplay between mechanical stresses and electrochemical reactions may lead to stress corrosion cracking or hydrogen embrittlement for many materials. In this work, the effect of the tensile stress on the electrochemical properties of AISI 304 stainless steel was studied using scanning Kelvin probe (SKP) in air and scanning electrochemical microscopy (SECM) in an aqueous 0.5 M Na₂SO₄ electrolyte. The measurements were performed under load- and load-free conditions. No influence of the elastic stress on the electrochemical potential of the steel was found. In contrast, the plastic strain induces dislocations and dislocation pile-ups, which emerge to the surface. The formation of new active surfaces is accompanied by an increase in the roughness and a 150–200 mV decrease in the steel potential. After activation, the potential increased due to passivation of the emerging surfaces by a newly grown oxide film, which took place under both the load and load-free conditions and followed a time dependence of φ = A log t + B. Formation and then passivation of the new surfaces increased and then decreased the reduction current of the mediator in the SECM measurements. The effect of residual stress stored in the steel due to the development of dislocations on the reactivity of the re-passivated surface was investigated.

Industrial coatings are composed of layers of different polymers (top coats, primers) containing pigments, corrosion inhibitors, and fillers as well as additives. For corrosion protection, it is vitally important to preserve the strong adhesion and long-term stability of the metal-polymer interface in corrosive environments. In recent decades, the performance of painted materials increased, which requires the application of advanced methods for quick assessing, ranking and predicting corrosion stability. Scanning Kelvin probe (SKP) is a highly sensitive and non-invasive technique to analyze in situ the metal-polymer interface of high-performance industrial coatings. SKP is able to monitor the adhesion and corrosion underneath different kinds of paints without the need for long-term corrosion tests. SKP is a localized electrochemical technique with a spatial resolution in the range of 70–100 μm. Hence, it is possible to obtain information about the intact and corroding portions of the interface at defect sites, corrosion blisters, contaminants, and intermetallics, quality of pretreatments, and the development of galvanic couples that lead to corrosion de-adhesion of the polymeric coatings. This article reviews the application of SKP to the determination of the mechanisms of corrosion de-adhesion of model paints, thick marine paints, coatings with zinc rich primers, automotive paints, and coil coatings applied on galvanized steel substrates.

Hydrogen in combination with mechanical stress can lead to rapid degradation of high-strength steels through environmentally assisted cracking mechanisms. The scanning Kelvin probe (SKP) was applied to automotive martensitic steel grade MS1500 in order to detect local reactivity of the surface after hydrogen uptake and tensile deformation. Hydrogen and stress distribution in microstructures can be characterized by SKP indirectly measuring the potential drop in the surface oxide. Thus, the links between electron work function, oxide condition, and subsurface accumulation of hydrogen and stress have to be investigated. It was shown that plastic strain can mechanically break down the oxide film creating active (low potential) locations. Hydrogen effusion from the steel bulk, after cathodic charging in aqueous electrolyte, reduced the surface oxide and also decreased potential. It was shown that surface re-oxidation was delayed as a function of the current density and duration of cathodic hydrogen pre-charging. Thus, potential evolution during exposure in air can characterize the relative amount of subsurface hydrogen. SKP mapping of martensitic microstructure with locally developed residual stress and accumulated hydrogen displayed the lowest potential.