Effect of simulated inflammatory conditions and potential on dissolution and surface oxide of CoCrMo alloy: In situ electrochemical atomic force microscopy study

Inflammation may develop in association with implantation of hip replacements and the inflammatory state of the local body fluids may affect the corrosion of metallic biomaterials like CoCrMo alloy. In this study CoCrMo alloy surfaces were imaged using in situ electrochemical atomic force microscopy (ECAFM) to evaluate oxide film morphology and surface dissolution while immersed in phosphate buffered saline (PBS) solution or simulated inflammatory (SI) solutions across a range of potentials. The SI solution explored here consisted of a 30 mM hydrogen peroxide (H2O2) modified PBS solution. Analysis of ECAFM images, surface roughness and potentiostatic polarization current density data exhibited a correlated relationship between surface oxide morphology, loss of passivity and electrochemical behavior CoCrMo alloy. ECAFM results showed that the presence of H2O2 altered oxide film behavior, leading to positive shifts of open circuit potential (OCP) to 0.32 V (vs Ag/AgCl), higher current density and significantly altered oxide film topography compared to PBS only case. Surface morphology, surface roughness (Ra) and current density exhibited strong potential- and time-dependent behaviors. Significant surface oxide formation on alloy and carbides were observed, followed by dissolution of CoCrMo alloy as potentials were increased above 0.5 V. Carbide boundaries and metal grain boundaries were preferential sites for oxide dissolution at transpassive potential ranges. Formation and evolution of new oxides were directly imaged at 0.65 V in PBS solution. New oxides formed and covered the surface in 10 min at 0.65 V. However, they were less protective compared to the passive oxide films at OCP condition. Simulated inflammatory solutions raise alter corrosion behavior of CoCrMo alloys.