The gross slip fretting corrosion mechanisms of biomedical ceramic-metal couples

Abstract

Fretting corrosion in taper joints is of concern since the mid-1970s. Thus, different metallic and ceramic material combinations have been tested and used clinically. While the stem is typically made of Ti-alloy the head materials can vary and may consist of CoCrMo-base alloys, alumina- or zirconia-based ceramics, and materials that rely on surface engineering. Based on retrieval analysis as to the acting mechanisms in real taper joints we tested some of these material combinations under gross slip fretting corrosion as one of the failure mechanisms at ultra-mild wear rates. We found that the main submechanisms for the generation of the tribomaterial (or 3rd-body) – which remains in contact and provides boundary lubrication – are microploughing, microcutting, and mechanical mixing, while the wear loss is brought about by the ejection of metal ions (and wear particles) and predominantly governed by the balance between tribocorrosion and triboxidation. We also showed that topography plays a major role under these circumstances. On the basis of ultra-mild wear gross-slip fretting corrosion experiments we demonstrated that non-self-mating combinations of Ti6Al4V against CoCr29Mo6 or zirconia-toughened alumina (ZTA) ceramic show a smaller wear loss provided that the reaction products can act as boundary lubricants. In addition, the material properties of bodies, counterbodies and the interfacial medium are also governed by the topographies in contact and their capability to act as reservoir for the tribomaterial. Hence, the fluted Ti6Al4V worked best against polished ZTA under these specific test conditions.