Anticorrosion and nanomechanical performance of hybrid organo-silicate coatings integrating corrosion inhibitors

Corrosion protective sol-gel silica coatings were developed on AA2024-T3 alloy by in situ cross-linking with hyperbranched poly(ethylene imine). Coatings with or without corrosion inhibitors (2-mercaptobenzothiazole or 2-mercaptobenzimidazole) and of two different thicknesses (1-1.5 and 3-3.5 μm, respectively) were obtained. Potentiodynamic scans and electrochemical impedance spectroscopy (after immersion in Harrison's solution for up to 4 weeks) were employed to evaluate the anticorrosion performance of coatings, whereas their thickness, morphology and integrity were assessed by scanning electron microscopy and atomic force microscopy. Further the depth sensing nanoindentation technique was employed to measure the hardness and reduced modulus of coatings and the obtained data were analyzed to indicate their wear resistance, plastic deformation and mechanical integrity. In all cases, coatings of high quality with good barrier properties (impedance modulus reaching up to 106 Ω cm2 at the very low frequency regime) and self-healing abilities (in case of the inclusion of an inhibitor) were obtained. The coating thickness was found to affect the anticorrosion performance, however, even thinner coatings demonstrate satisfactory protection and self-healing effect. Nanoindentation analysis revealed the flexible nature and viscous behavior of the coatings (with the theoretical transition of the elastic to plastic behavior appearing at 1000 μN applied load) demonstrating also an optimal integration of the organic inhibitors into the film. It also revealed an effect of thickness with thinner coatings exhibiting slightly superior behavior in terms of elasticity and wear resistance.