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

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.