Wear is still the main problem causing the failure and limiting the lifetime of metal-on-metal (MoM) artificial hip joints. The continuous release of nano-sized metal particles and ions into the body is of long-term concern as it can cause allergies and other toxic reactions. Tribocorrosion, which is the interaction of mechanical wear and electrochemical corrosion has been proposed as the crucial wear mechanism of MoM hip joints and recently saw significant progress in mechanistic understanding and modeling. However, these studies neglect in the overall degradation the lubrication effects provided by synovial fluid in human body. Indeed, studies already showed a clear relation between wear and hydrodynamic lubrication of MoM hip joints.
A wear model for passive metals based on the plastic deformation of contacting metal asperities which considers mechanical wear, electrochemical corrosion and fluid lubrication aspects was proposed in this study to quantitatively describe and predict material degradation.
As applied to CoCrMo sliding tribocorrosion contacts, the model predicts remarkably well wear rates observed in tribometers and the running-in wear rate in simulators. In the case of MoM hip joints, the model predictions concerning the effect of crucial parameters such as head radius and clearance closely correlate with experimental observations. The model emphasizes the need of better understanding the electrochemical conditions established in artificial joints.