Mixed-metal fretting corrosion of Ti6Al4V and wrought cobalt alloy.

Corrosion has been reported at the modular interfaces of total joint replacement implants, but with conflicting theories as to the cause of such damage. The modular design itself leaves the interface susceptible to galvanic, crevice, or fretting corrosion, or a combination of the three. The purpose of this study was to quantify the effect of material combination on fretting corrosion of orthopedic alloys. Each test specimen consisted of a two-hole plate with spherical countersinks and two cortical bone screws. The plates and screws were made of either Ti6Al4V or wrought cobalt-chromium-molybdenum (CCM), and were tested in all mixed-metal and similar-alloy combinations. Fretting corrosion experiments were conducted for 14 days in 10% calf serum, according to ASTM F897. Corrosion damage was evaluated by weight-loss measurements, atomic absorption spectrophotometry and scanning electron microscopy analyses. The results indicated that Ti6Al4V suffered relatively severe damage when fretted against itself, as a result of adhesive galling. The extent of titanium damage was reduced considerably, however, when Ti6Al4V was fretted against wrought CCM. In contrast, there was essentially no difference in wrought CCM damage when the alloys was fretted against itself compared to fretting against Ti6Al4V. Finally, in similar-alloy combinations, Ti6Al4V suffered more severe damage than wrought CCM.