CoCrMo alloys used for biomedical applications are often exposed to the combined effect of mechanical wear and electrochemical corrosion. Tribocorrosion tests have been performed in this work to investigate the repassivation kinetics of a HC CoCrMo alloy in four different solutions commonly used to simulate body fluids. The repassivation kinetics are analysed by fitting two different exponential equations. The comparison of the different equations reveals that that a second order exponential equation models the repassivation currents more closely than a first order exponential equation. A repassivation model based on a second order exponential equation is suggested. The repassivation currents are divided in two main phases, a ’coverage’ phase and a ’film thickening’ phase. At the initial stage, when part of the surface is exposed to the corrosive media, higher potentials lead to faster repassivation rates. By contrast, potential does not have a clear effect at the thickening phase, when the material is protected by the oxide film formed on top of the surface.Conclusions The repassivation kinetics of a CoCrMo alloy have been investigated.
Conclusion:
- A second order exponential decay represents the repassivation of the studied CoCrMo alloy more closely than a first order exponential decay under the studied conditions.
- The repassivation phenomena can be divided in two phases. First, at the coverage phase, the formation of oxide film that deposits and covers the mechanically damaged part of the surface governs the equation. Second, at the film thickening phase, most of the surface is already repassivated and the thickness of the oxide film grows, being this reaction dominant.
- The coverage phase is dominated by the fraction of the surface covered by oxide, whereas the thickness of the reformed passive layer dominates the currents measured during the thickening phase.
- The faster repassivation observed at higher potentials at the initial of the repassivation phase or coverage phase indicates that a fraction of the base alloy is exposed to the media, increasing the reactivity of the material.
- Sample potential does not have a clear effect on the repassivation time constant at the second repassivation stage or thickening stage because the sample is protected