In biomedical field, fretting-corrosion between 316L SS femoral stem and bone cement is one of the significant causes of the hip prosthesis loosening. This article investigates wear by fretting-corrosion at the contact between 316L and PMMA . The influences of the ionic strength (NaCl solutions from 10 -3 to 1 mol.L -1 ), a model protein (albumin) and electrochemical conditions on contact behaviour are studied. At OCP (Open Circuit Potential) conditions, the chlorides concentration, i.e. the ionic strength, increases the 316L wear; and albumin, concentration of 1g.L -1 , does not play a significant role in total 316Lwear. At cathodic applied potential E = -400 mV(SCE), a threshold concentration of 10 -1 mol.L -1 (NaCl solution), C th , indicates two behaviours: a protective effect below C th , and an additional anodic dissolution above C th . One might suggest that, beyond C th , the passive layer is not efficient for protecting against the corrosion. At this potential, albumin reduces wear due to corrosion and amplifies mechanical wear induced by corrosion. Albumin seems to act as an anodic inhibitor. To determine the mechanisms of synergism, a "more cathodic" potential is applied, E = -800 mV(SCE), during fretting-corrosion experiments.Consequently, the corrosive wear can be neglected and the mechanical wear can be only measured.
The permeation of hydrogen in steel in the presence of acid gases is not a simple phenomenon as the steel may contain trapping sites and also because the permeation may be governed by surface reactions associated with corrosion. Recently, hydrogen permeation experiments carried out at the corrosion potential have shown a constant flux for various membrane thicknesses in the range 0.05-0.8 mm. These results revealed the difficulty to express the flux for thicker steel membrane (i.e. pipe) from laboratory studies on thin membranes, as the classical rule (flux proportional to the inverse of the membrane thickness) is not always applicable and not conservative. This paper presents new permeation results, obtained on steel membranes up to 10 mm thick. The transition between thin and thick membranes is clearly established, and is in the millimeter range in sour conditions. The necessity to adopt a new interpretative framework to link permeation measurements and hydrogen cracking mechanisms is reinforced. For thin membranes, the permeation flux is constant and governed only by the charging flux crossing the entry face. This surface mechanism is probably correlated with surface cracking mode, like SSC. On the other hand, the traditional concept of diffusion can only be used in thick membrane situations. The diffusion flux is inversely proportional to the sub-surface concentration. This concentration is in direct relation with the hydrogen activity in the steel, which is probably correlated with internal cracking modes, like HIC.
International audienceIn the case of hip prostheses, debris generation, due to the fretting-corrosion phenomenon between the femoral stem and the bone cement is one of the most significant causes of reintervention. In this study we use atomic force microscopy (AFM) to analyze PMMA particles and pitting corrosion on 316L SS as a function of chlorides and albumin concentration. Without albumin, the number of pits increases with the chlorides concentration. Contrary to the protective effect of albumin on global corrosive wear, albumin tends to increase the number of pits. The number of ejected particles highly depends on electrochemical conditions and the in vivo conditions, Open Circuit Potential, seem to lead to a small number of particles. This work has also explored atomic force microscopy as a "new" characterization technique for wear debris and demonstrates that 80% of particles have a size inferior to 100 nm, which is the 'critical size' for tissues response
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