Applicability of a recently proposed tribocorrosion model to CoCr alloys with different carbides content

Existing sliding tribocorrosion models have been developed for homogeneous passive metals such as stainless steel and pure metals. Many technical alloys contains however second phases, usually much harder than the metallic matrix, intended to provide better mechanical properties. The tribocorrosion models are based on the assumption of nearly perfect plastic behavior that is not necessarily representative of the tribological response of inhomogeneous metals. This work was initiated with the aim of evaluating the applicability to inhomogeneous alloys of a recently developed tribocorrosion model that includes mechanical, chemical and lubrication phenomena. For this the tribocorrosion of three different CoCr alloys was investigated using a reciprocating ball (alumina)-on-plate tribometer in a 0.5 M sulfuric acid solution. The alloys studied were a Stellite 6 (S6) with 22% of carbides, a Stellite 21 (S21) with 6% of carbides and a Stellite 21 (LCS21) without carbides. Tribocorrosion tests were carried out under potentiostatic conditions under different loads. Scanning electron microscopy, laser profilometry and focused ion beam were used for surface and sub-surface characterization of the wear tracks. The results obtained with the S21 and LCS21 alloys are consistent with the model while in the case of alloy S6, exhibiting interconnected carbide phases, the model correctly describes the corrosion response but only approximately the mechanical release of wear particles.