Corrosion behaviour of CoCrMo implant alloy during fretting in bovine serum

CoCrMo alloys in dental skeletal structures and orthopaedic implants are susceptible to mechanical disruption of the passive film. To study this effect the open circuit potential (ocp) of CoCrMo alloy before, during and after mechanical disruption of the passive film in a tribo-electrochemical cell is recorded in serum and inorganic buffered solutions at pH 4.0 and 7.0. The ocp values achieved during rubbing (rubbing potentials) in serum are in agreement with a reaction mechanism whereby the anodic dissolution reaction involves the formation of the aqueous cations Co(II) and Cr(II) at acidic pHs and the oxides CoO and CrO at neutral and alkaline pHs. It is suggested that the kinetics describing the anodic dissolution reaction of the alloy in serum is under diffusion control, which is responsible for more positive rubbing potential values observed compared to inorganic solutions at the same pH. The corrosion current of the alloy is significantly lower in serum both at pH 4.0 and 7.0. In addition, the biological electrolyte increases the repassivation rate at neutral pH.