Tribocorrosion behavior of S-phase surface engineered medical grade Co–Cr alloy

Co–Cr alloy is one of the most widely used metallic biomaterials for metal-on-metal joint prostheses. However, concerns about increased revision rates associated with large head metal-on-metal replacements have been raised recently. Release of such toxic ions as Cr and Co from corrosion–wear induced nano-sized wear debris has been envisaged as the potential cause. This research was aimed at studying the tribocorrosion behavior of S-phase surface engineered medical grade ASTM F1537 Co–Cr alloy with a view of addressing problems associated with current metal-on-metal joint prostheses. To this end, ASTM F1537 Co–Cr alloy surfaces were plasma alloyed with carbon at low-temperature to produce a surface carbon S-phase layer, which is a precipitate-free carbon super-saturated solid solution with high hardness, good corrosion and wear resistance. Cyclic potentiodynamic and potentiostatic measurements were performed under unidirectional sliding wear condition in 1 M Ringerʹs solution to evaluate tribocorrosion properties of the low temperature plasma treated as well as untreated ASTM F1537 Co–Cr alloy. The results showed that the S-phase layer can significantly enhance the tribocorrosion properties of Co–Cr alloy in terms of reduced corrosion potentials and wear volume. The much improved tribocorrosion behavior of the S-phase layer can be attributed to its high hardness, good corrosion resistance and excellent repassivation ability.