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National audience; Some implants have approximately a lifetime of 15 years. The femoral stem, for example, should be made of 316L/316LN stainless steel. Fretting corrosion, friction under small displacements, should occur during human gait, due to repeated loadings and un-loadings, between stainless steel and bone for instance. Some experimental investigations of fretting corrosion have been practiced. As well known, metallic alloys and especially stainless steels are covered with a passive film that prevents from the corrosion and degradation. This passive layer of few nanometers, at ambient temperature, is the key of our civilization according to some authors. This work is dedicated to predict the passive layer thicknesses of stainless steel under fretting corrosion with a specific emphasis on the role of proteins. The model is based on the Point Defect Model (micro scale) and an update of the model on the friction process (micro-macro scale). Genetic algorithm was used for finding solution of the problem. The major results are, as expected from experimental results, albumin prevents from degradation at the lowest concentration of chlorides; an incubation time is necessary for degrading the passive film; under fretting corrosion and high concentration of chlorides the passive behavior is annihilated. // Les implants orthopédiques de hanche ont une durée de vie d'environ 15 ans. Par exemple, la tige fémorale d'un tel implant peut être réalisée en acier inoxydable 316L ou 316LN. Le fretting corrosion, frottement sous petits déplacements, peut se produire pendant la marche humaine en raison des chargements répétés entre le métal de la prothèse et l'os. Plusieurs investigations expérimentales du fretting corrosion ont été entreprises. Cette couche passive de quelques nanomètres, à température ambiante, est le point clef sur lequel repose le développement de notre civilisation, selon certains auteurs. Ce travail vise à prédire les épaisseurs de cette couche passive de l'acier inoxydable soumis au fretting corrosion, avec une attention spécifique sur le rôle des protéines. Le modèle utilisé est basé sur le Point Defect Model, PDM (à une échelle microscopique) et une amélioration de ce modèle en prenant en compte le processus de frottement sous petits débattements. L'algorithme génétique a été utilisé pour optimiser la convergence du problème. Les résultats les plus importants sont, comme démontré avec les essais expérimentaux, que l'albumine, la protéine étudiée, empêche les dégradations de l'acier inoxydable aux plus faibles concentrations d'ions chlorure ; ensuite, aux plus fortes concentrations de chlorures, un temps d'incubation est nécessaire pour détruire le film passif.

International audience; This work aims at investigating experimentally fretting corrosion, that is, corrosion induced by friction of AISI 316L SS against poly(methyl methacrylate) under small displacements. The observed wear on the stainless steel has been modeled using the Point Defect Model (PDM). The originality of this approach in applying the PDM to fretting corrosion consists of using a modified rate of the barrier layer dissolution, in the case of cyclical wear, such that the rate of destruction of the barrier layer at the barrier layer/solution interface exceeds the rate of barrier layer growth at the metal/barrier layer interface at zero barrier layer thickness, which is the condition specified by the PDM for depassivation. By optimization of the PDM on experimental electrochemical impedance data under fretting conditions, we have been able to ascertain values for various model parameters, and to calculate the steel volume loss as a function of potential.

Previous studies on the formation of passive oxide films on iron have been done, giving good agreements with experimental data on how the thickness of the oxide film depends on the electrolyte solution's pH and on the applied potential. In this study we follow in the steps of a series of publications that addressed the formation and semiconducting properties of iron oxide (particularly the Fe3O4 ) in borate buffer solutions with a pH of 8.4, undertaking a numerical simulation, using the finite element method (FEM), of a 1D steady state system comprising a passive film on an rotating disk electrode (RDE) of Fe in contact with an electrolyte solution. A set of diferential equations was solved using the finite element method in the simulation framework MuPhyS (Multi-Physics-Solver), developed by the research group SURF at the Vrije Univesiteit Brussel. The main chalange was to link the two physical domains using the point defect reactions model for the oxide layer domain and the balance model for both the electrolyte solution and the oxide layer domain; the results of our simulations show and conrm some of the reported conclusions in earlier studies related to the use of PDM with iron oxides.

Passivity of chromium in 0.5 M sulfuric acid has been explored using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The results of potentiostatic measurements have shown that the passive current density is potential-independent, while the thickness of the passive layer increases linearly on the applied potential, which is consistent with the postulation of the Point Defect Model. The Mott-Schottky analysis revealed that the passive film is an n-type semiconductor (related to the outer Cr(OH)3 layer). No evidence for p-type behavior was obtained, indicating that the cation vacancies do not have a significant population density in the film compared with the two donors (cation interstitial and oxygen vacancies). The transpassive state comprise a thick, porous oxide film on the surface, with characteristics consistent with the oxidative ejection of Cr(VI) species from the barrier layer.