Corrosion protection of 304L stainless steel by chemical vapor deposited alumina coatings

Abstract

The corrosion protection of 304L stainless steel by aluminium oxide coatings deposited by metal-organic chemical vapor deposition (MOCVD) was investigated in a 0.1 M NaCl solution at room temperature by polarization curves and electrochemical impedance spectroscopy. The effect of the coating thickness was specifically considered. Transmission electron microscopy cross-section observations of the stainless steel/alumina coating showed that the coating is amorphous and porosity-free. The impedance response, for short immersion times, confirmed the absence of porosity and revealed that the alumina coatings with thickness ranging from 250 nm to 1700 nm provide high corrosion resistance. The corrosion protection increased when the alumina coating thickness increased. However, from the impedance data obtained for different exposure times to the aggressive solution, a threshold film thickness of 500-600 nm was determined, above which the corrosion protection was not improved. Due to their interesting physicochemical properties, such films of amorphous alumina are an innovative and economically accessible alternative to improve the stainless steel corrosion resistance and could be used in miniaturized sensors operating in marine environment. c-Al 2 O 3 takes place. Deposition temperature also impacts the composition of the films: combined electron probe microanalysis (EPMA), Rutherford backscattering spectroscopy (RBS) and energy-dispersive X-ray spectroscopy (EDS) showed that, for films processed at 350°C, the O/Al ratio is equal to 2. For these films, Fourier transform infrared spectrometry (FTIR) revealed the presence of OH groups, with the overall composition corresponding to that of aluminium oxy-hydroxide, AlOOH. With increasing deposition temperature, the O/Al ratio and the concentration of OH groups gradually decrease to reach a composition which matches

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