Analogy between the effects of a mechanical and chemical perturbation on the conductivity of passive films

In order to study the passivity breakdown of a type 316L stainless steel, the electrochemical impedance and surface stresses were measured under straining conditions. The Mott-Schottky analysis, performed at high frequency, appears as very useful method to study, below the apparent yield strength, the effects of a mechanical stress on the capacitance values. The results obtained in sodium chloride media indicate that the semiconducting properties of passive films formed in a tensile stress field reflect a higher vacancies concentration than those formed in a stress-free state, suggesting that the passive film conductivity is increased. It was also shown that the Mott-Schottky plots drop in the presence of tensile surface stresses, indicating that the passive film composition may be different from that formed in the presence of compressive surface stresses. A comparison between the effects of mechanical stresses and those of chloride is proposed. (C) 22002 Elsevier Science Ltd. All rights reserved.