Corrosion Resistance of Oxide Coated Stainless Steel by Sputtering

Abstract

To improve the corrosion resistance of stainless steels, corrosion behavior of stainless steel with various sputtering-deposited oxide films, in acidic solutions, was studied. The effect of pinholes, inevitable structural defect in sputter coated oxides, on the corrosion protection properties of these films were examined. With a single, RF magnetron sputter-deposited, layer of oxide coating, the corrosion resistance was greatly improved compared to the non-coated stainless steel. Polarization experiments show the passive current density to be influenced by the pH_pzc (pH of zero charge of the oxide).
The defect probability was determined using both electrochemical measurements and optical method using nematic liquid crystals. The good correlation of the results between these two methods indicates that either method is available to determine the defect density of thin films. For double-layer coated oxide films, the effect of pH_pzc was clearly observed. In cases where the inner oxide layer possesed a higher value of pH_pzc, the corrosion resistance was proven to be greater. The effect is explained by the difference in ion migration through the coated films.