A study of the potentials achieved during mechanical abrasion and the repassivation rate of titanium and Ti6Al4V in inorganic buffer solutions and bovine serum

Titanium alloys in orthopaedic implants are susceptible to mechanical disruption of the passive film (fretting corrosion). To study this effect, open-circuit potential (ocp) measurements before, during and after mechanical disruption of the passive film in a tribo-electrochemical cell on commercial pure titanium and Ti6Al4V alloy in inorganic buffer solutions in the pH range from 2.0 to 12.0 and calf bovine serum at pH 4.0 and 7.0 are reported. Additionally, the effect of pH, electrolyte and sample composition on the repassivation rate has been investigated. The potentials achieved during the abrasion of Ti6Al4V are the same as those characterizing pure titanium, which indicates that the corrosion current of both materials in the active state is due to the oxidation of titanium. However, commercial pure titanium displays a tendency to repassivate faster than Ti6Al4V in inorganic buffer solutions thanks to the lower critical current density and the higher catalytic activity towards the hydrogen evolution reaction observed on the pure metal in comparison with the alloy. Proteinaceous solutions like bovine serum significantly slow down the anodic dissolution and the cathodic reactions both on titanium and the alloy. However, the repassivation rate of the Ti6Al4V is not affected by serum, while that of cp titanium significantly decreases both at pH 4.0 and 7.0.