Characterization of SiO2-TiO2 Coatings on 316l Stainless Steel Substrates

This paper reports nano-structured SiO2-TiO2 coatings using the sol-gel technique on 316L steel substrates. Nanoindentation, surface analysis and corrosion resistance tests were performed on different samples. The nanomechanical tests allowed to compare uncoated steel samples (Eavg = 193.24 GPa and mean hardness of 2.63 GPa and coated steel samples (Eavg = 287.38 GPa and mean hardness of 5.74 GPa), resulting into an improvement of the resistance and modulus of elasticity on the coated steel substrates. From a surface analysis an average thickness of 1.12 μm was obtained in the coated samples, presenting a dense and consolidated coating. Polarization resistance (PR) and electrochemical impedance spectroscopy (EIS) tests were performed. The PR tests showed a resistance of 2.11  105 (Ω cm2) for the uncoated steel, while the coated steel showed a resistance of 3.46  105 (Ω cm2), observing an increase in resistance compared to bare steel. The EIS tests showed greater resistance by the coated steel (5.8  105 (Ω cm2)) compared to the bare steel (2.8  105 (Ω cm2)). The effects of the electrolyte in both conditions were observed by SEM after immersion for 24 hours, showing pitting by the bare steel and good protection by the coated steel.