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Load bearing implant prostheses such as orthopaedic hip and knee implants may be considered as tribocorrosion systems since the wear processes are a result of combined mechanical and chemical mechanisms. The long-term success of implant prostheses depends on a number of factors, including age, body weight and activity levels. Pre-clinical testing is therefore crucial in determining the long-term performance, safety and reliability of the implant in-vivo. In this study CoCrMo alloy and UHMWPE couple was tested in a physiological solution of foetal calf serum (FCS) in 0.9 wt. % NaCl to assess the underlying wear mechanisms as a result of applied load (0-5N) and applied potential (-600, -400, -200, 0 and +200 mV). The transitioning behaviours due to micro-abrasion and corrosion were studied; corresponding micro-abrasion-corrosion wear maps were constructed to indicate the mass loss transitions in scope of wastage, mechanisms of wear and synergies between abrasion-corrosion for simulated hip contact conditions.

The micro-abrasion wear mechanisms for CoCrMo against variable size alumina balls, representing typical artificial femoral head sizes, were investigated over a range of applied loads in foetal calf serum solution. SEM analysis of resulting wear scars displayed two-body and mixed-mode abrasion modes of wear. The wear factor, κ, was found to range between 0.86 and 22.87 (10−6 mm3/Nm). Micro-abrasion mechanism and wastage maps were constructed for the parameter range tested. A dominant two- to three-body abrasion regime was observed with an increasing load and ball diameter. The 28-mm ball diameter displayed the lowest wastage, with an increasing load. Proteins may act to reduce the severity of contact between abrasive particles and bearing surfaces. Wear volumes did not necessarily increase linearly with applied load and ball diameter; therefore, there is a need to develop more accurate models for wear prediction during micro-abrasion conditions. Wear mapping for hip replacements could provide a useful aid for pre-clinical hip wear evaluations and long-term performance.