Investigation of Long-Term Corrosion of CoCrMoW Alloys under Simulated Physiological Conditions

Abstract

The corrosion resistance of two cast CoCr-based alloys with different amounts of chromium and with different alloying elements in the bulk composition of the alloy was assessed. In this study, we investigated the corrosion behavior of Co21Cr8Mo7W and Co29Cr7W by open-circuit potential (OCP), potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS) in 0.1 M phosphate buffer solution (PBS) at 37 °C with long immersion times. After 1000 h of immersion, the corrosion current density (icor), estimated from anodic polarization tests, was lower for the Co21Cr8Mo7W (i.e., 49 nA cm−2) alloy compared to the Co29Cr7W alloy (180 nA cm−2). As regards the corrosion potential (Ecor), a greater value was observed for Co21Cr8Mo7W (i.e., −59 mV vs. Ag/AgCl) compared to Co29Cr7W (i.e., −114 mV vs. Ag/AgCl). Microstructure analysis before and after immersion revealed the formation of a more compact passive film on the Co21Cr8Mo7W alloy, suggesting superior corrosion resistance compared to Co29Cr7W. These findings suggest better corrosion resistance for the film formed on the alloy containing lower amounts of Cr and two alloying elements, Mo and W. These results are promising in terms of medical applications because they open the door to new strategies for obtaining alloys with lower chromium content and with more protective anti-corrosion properties.