Fretting corrosion behaviour of Ti-6Al-4V alloy in artificial saliva containing varying concentrations of fluoride ions

Abstract

The present communication addresses the fretting corrosion behaviour of Ti–6Al–4V alloy in artificial saliva containing 0, 190, 570 and 1140 ppm of fluoride ions. The fretting corrosion behaviour of Ti–6Al–4V alloy was evaluated based on the change in free corrosion potential (FCP) measured as a function of time. The wear morphology and surface profile of the fretted zone, assessed by scanning electron microscopy and non-contact optical profilometer, were used to ascertain the wear mechanism. The cathodic shift in FCP observed with the onset of fretting indicates damage of the passive film. After the fretting motion is ceased, an instantaneous repassivation of Ti–6Al–4V alloy is observed only in artificial saliva. The negative influence of fluoride ions on passive film formation hinders instantaneous repassivation of the damaged areas of the fretted zone. The morphology of the fretted zone reveals the occurrence of adhesive galling in all the cases. The wear volume of the fretted zone of Ti–6Al–4V alloy in artificial saliva free of fluoride ions is 3.26×1012 nm3. In presence of 190ppm of fluoride ions in artificial saliva, the wear volume is increased from 3.26 to 9.87×1012 nm3. However, the wear volume is reduced to 6.95×1012 nm3 and 3.60×1011 nm3 at 570 and 1140ppm of fluoride ions, respectively. The change in contact configuration from alumina–titanium to titanium-coated alumina–titanium reduced the mutual solubility between alumina and titanium, the extent of trapping and grinding of the wear debris and the wear rate of Ti–6Al–4V alloy in artificial saliva containing 1140 ppm of fluoride ions. The study reveals that the fretting corrosion behaviour of Ti–6Al–4V alloy in artificial saliva shows a strong dependence on the fluoride ion concentration.