Near surface analysis of duplex PIII treated CoCr alloys

The formation of expanded austenite in CoCr alloys is a well established process for forming hard and wear resistant surfaces for biomedical applications. However, even nitrogen implantation at reduced temperatures of 350 °C, where no CrN formation is observed, leads to a significant increase in the corrosion current, together with selective release of Co ions. By using a duplex nitrogen/oxygen process, a strong reduction of the corrosion rate is possible when the processing temperatures are limited to 300–350 °C. Detailed investigations into the chemical environment imply that a strong influence of grain boundaries or defects on the corrosion rate exists, which is not visible when measuring XPS spectra across a sufficiently large surface area.