CORROSION BEHAVIOR OF TI-6AL-4V IN PHOSPHORIC-ACID

Ti-6Al-4V shows distinct active-passive behaviour in phosphoric acid o ver a wide concentration range. The cathodic polarization curves are s imilar over a wide range of acid concentration and temperatures. The a lloy undergoes active dissolution and turns passive in the negative po tential region followed by a wide range of passivity at all acid conce ntrations at different temperatures. Increasing acid concentration up to 11 M results in an increase in critical current density (i(cr)). Th e passive current density (i(p)) increases up to an acid concentration of 9 M while at 13 M i(cr) and i(p) decrease appreciably. A significa nt increase in both i(cr) and i(p) occurs with increase in solution te mperature. The passive specimen remained stable for a long time when e xposed to phosphoric acid under open circuit conditions.