Electrochemical Impedance Spectroscopy Study of Corrosion Resistance of RF-Sputtered Titania Thin-Film-Coated SS316 in 3.5 wt.% NaCl

Corrosion of stainless steel in chloride-containing environments remains a critical challenge for industrial applications, particularly in marine, chemical processing, and oil and gas systems, necessitating durable protection strategies. In this study, the corrosion behavior of AISI SS316 in 3.5 wt.% NaCl solution was investigated before and after application of titanium dioxide (TiO₂) thin-film coatings deposited using radiofrequency sputtering. The objective of this work was to evaluate the influence of a thin-film barrier on the electrochemical response and corrosion kinetics of stainless steel exposed to a simulated seawater environment.

Electrochemical Impedance Spectroscopy (EIS) and linear polarization techniques were employed to assess corrosion resistance and mechanisms of bare and coated specimens. Impedance measurements were conducted over a frequency range of 0.1 Hz to 1 MHz to evaluate coating integrity, charge transfer resistance, and capacitive behavior at the metal–electrolyte interface. Corrosion rates were determined using polarization resistance measurements and Tafel extrapolation methods to quantify kinetic parameters.

The EIS results demonstrated a significant increase in impedance and charge transfer resistance for TiO₂-coated SS316 compared to the uncoated substrate, indicating improved barrier properties and reduced electrochemical activity in chloride-rich solution. Linear polarization data confirmed a reduction in corrosion rate for coated specimens, validating the protective effectiveness of TiO₂ thin-film. Enhanced corrosion resistance is attributed to the formation of a dense and chemically inert TiO₂ layer that restricts electrolyte penetration and suppresses anodic and cathodic reactions on the stainless steel surface. The TiO₂ thin film also acts as a diffusion barrier limiting oxygen transport to the metal surface, reducing electrochemical activity at the metal–electrolyte interface. This behavior is relevant in chloride environments where localized corrosion mechanisms, including crevice corrosion, may be influenced by oxygen availability.

These findings highlight the potential of RF-sputtered TiO₂ thin-film coatings as a durable corrosion protection strategy for stainless steel components operating in chloride-containing environments.