Surface and subsurface changes as a result of tribocorrosion at the stem-neck interface of bi-modular prosthesis

This study presents a detailed multi-scale analysis of the degradation processes occurring on both the CoCrMo and TMZF alloy surfaces at different regions across the taper interface. Co-ordinate measurement machine, scanning electron microscopy, transmission electron microscopy and X-ray diffraction methods have been utilised to identify the roles of degradation from the mm to nm scale. Depending on the region of interest, varying topographies and subsurface morphologies were observed across both surfaces. In regions where high pressures are expected, retention of the surface topography was seen on the CoCrMo trunnion. This was complimented by gross shear and plastic deformation of the subsurface material. In regions where maximum penetration was seen, evidence of fretting-corrosion was seen and a loss of the nano-crystalline layer. For the TMZF surface, refinement of the alloy was seen in the top 5 μm, with fatigue cracks within the bulk present. Precipitation and formation of oxide species were observed at depths of 2 μm. The degradation of a bi-modular prosthesis is a complex multifactorial process. It is hypothesised that this formation of oxide species at the interface and within the bulk alloy plays an important role in the degradation through a combined work-hardening and corrosion process.