VI - Études par microscopie à champ proche des films passifs formés sur les aciers inoxydables

Applications à la corrosion sous contrainte

AFM and STM studies of passive films formed on stainless steels. Applications to stress corrosion cracking

Abstract

Modelization of crack propagation and theoritical prediction of rupture are the two main objectives of researchers in stress corrosion cracking. Nevertheless, to reach this aim, the behavior of the passive film which appears spontaneously on the substrate in contact with an environment has to be known. This structural and mechanical characterization is all the more difficult because the number of parameters is important : cristallinity rate, defects concentration, thickness (about a few nanometers), electric field, chemical composition (a lot of oxides are present), peeling capacity, etc… In this condition, the near field microscopy (AFM or STM) gives us important informations about these layers (atomic structure for example) and some hypothesis can be made about their multi-layer structure, their chemical composition or their epitaxial character..,

Passive films formed on 316L or 304L stainless steels in different aqueous solutions (in ambiant air, in MgCl₂ at 117°C…) have been studied and some important remarks about their mechanical properties are made (brittle behavior, strong or weak adherence stress between the oxide and the substrate).