Corrosion behavior of pure titanium and titanium alloys in various concentrations of Acidulated Phosphate Fluoride (APF) solutions.

The corrosion behaviors of Ti, Ti-6Al-7Nb and Ti-6Al-4V alloys, and an experimentally produced Ti-0.5Pt alloy in 0.05% to 2.0% concentrations of Acidulated Phosphate Fluoride (APF) solutions (corresponding to 226 to 9,050 ppm fluoride at pH 3.5 or 3.6) were examined. While the corrosion of Ti, Ti-6Al-7Nb and Ti-6Al-4V alloys might occur easily even in a diluted 0.05% APF solution, dissolution of Ti from the Ti-0.5Pt alloy was observed only in test solutions with APF concentration exceeding 0.2%. When Ti-6Al-7Nb and Ti-6Al-4V alloys were immersed in 2.0% APF solution, their surfaces were entirely covered by compact corrosion products of Na3TiF6 due to severe corrosion. As a result, Ti dissolution was prevented and the amount of Ti dissolved decreased. However, since Ti was covered by porous, large-sized corrosion products of Na3TiF6 and that Ti-0.5Pt alloy was not covered with any corrosion product, the amount of Ti dissolved increased in the 2.0% APF solution.