Corrosion pits in thin films of stainless steel

Thin stainless steel films were prepared by sputter deposition onto silicon substrates using a 304 stainless steel target. The film composition was essentially that of 304 stainless steel, but they had a body-centered cubic structure and were free of sulfide inclusions. Potentiodynamic polarization curves were obtained for thin films in various chloride-containing solutions and compared to results from conventional stainless steel samples. In addition, video images of two-dimensional pits in thin films were used to determine the anodic pit current density as functions of potential and chloride concentration. Thin stainless steel films were found to be significantly more resistant to pit initiation than their bulk counterparts, but pit propagation was possible at relatively low potentials. A diffusion-controlled growth regime was identified at high potentials, with a transition to mixed activation/ohmic control at lower potentials (just above that required for repassivation). (C) 1999 The Electrochemical Society. S0013-4651(98)04-038-5. All rights reserved.