High-corrosion-resistant Al2O3 passivation-film formation by selective oxidation on austenitic stainless steel containing Al

Abstract

We have developed Al2O3 passivation film having very high anticorrosion resistance on the surface of austenitic stainless steel containing 3 wt % aluminum. Al2O3 passivation film is formed by selective oxidation of aluminum in the austenitic stainless steel in the Ar and H2 ambient including a small amount of H2O at predetermined temperatures. Al2O3 film is obtained at temperatures higher than 750 °C in the Ar and H2 ambient, where the partial pressure ratio of H2 and H2O is set higher than 2×103. Al2O3 films have been confirmed to exhibit very high anticorrosion resistance for various halogen gases and various plasma ambients (Cl2, H2, and O2) with ion-bombardment energies less than 100 eV at temperatures less than 150 °C. In the case of fluorine-gas plasma, the Al2O3 film surface has been converted to AlF3 with a depth of 15 nm, where AlF3 film is thermodynamically stable, as well as Al2O3, resulting in an excellent passivation film exhibiting very high anticorrosion capability. Moreover, the Al2O3 film surface has been confirmed to exhibit no catalytic activity for various specialty gases at temperatures less than 150 °C.