Post-annealing effect on the electrochemical behavior of nanostructured magnetron sputtered W3O films in chloride- and acid-containing environments

Abstract

In this study, magnetron sputtered tungsten oxide (W 3 O) thin films were deposited on stainless steel 316L substrates followed by annealing treatment at different temperatures (200 to 800 °C). The synthesized films were characterized and thereafter investigated for their corrosion resistance behavior, in both 3.5% NaCl and 0.5 M H 2 SO 4 environments, using electrochemical corrosion techniques. FESEM, XRD, and XPS analyses revealed that the oxygen content increases with annealing temperature, which then results in morphological and microstructural changes from cubic nanorods to monoclinic nanoplatelets and nanopyramids, composing of mixed oxidation states (WO 2.72 and WO 2.92 ). Electrochemical impedance and potentiodynamic measurements showed that in the chloride-containing solution the resistance increases with the annealing temperature until an optimum temperature of 400 °C. Similarly, the as-deposited and the films annealed at temperatures up to 400 °C demonstrated better protectiveness that exceeds 95%, in the acidic environment. The passive current densities and the pitting potentials of the films were likewise improved in both environments. Findings in this investigation suggest that an annealing temperature of 400 °C induced optimum protective barrier properties to the film. • Magnetron sputtered W 3 O films were fabricated on 316L stainless steel substrates. • Post-annealing effect at different temperatures on corrosion behavior was assessed. • This results in structural changes from cubic nanorods to monoclinic nanopyramids. • Corrosion and pitting resistance of the films in 3.5%NaCl and 0.5MH 2 SO 4 is improved. • Annealing at 400 °C induced optimum corrosion resistant properties to the W 3 O film.