An investigation on dissolution and passivation behaviour of Ti-6AI-4V in sulphuric acid

Potentiostatic technique has been employed to investigate the polarization behaviour of a titanium alloy (Ti-6Al-4V) in a wide concentration range (1-17 M) of sulphuric acid, at 30°C and 40°C. Effect of temperature variation of the experimental solution has been studied in selected concentrations (5M and 9M) of the acid. The cathodic current density increased in accordance with increasing acid concentration, temperature and applied potential. Anodic polarization studies showed active-passive transition and broad passivity range of potential available for the stability of alloy. The critical current density and passivity current density. (i c and i p ) increased with an increase in the concentration and temperature of the solution. However, these values decreased in solution above 11M sulphuric acid. The passivated specimen revealed formation of uniform and stable anodic film during longer exposure time. Apparent activation energy, obtained from Arrhenius plots, corresponding to critical current densities is of order for the chemical reaction. Impedance measurements indicate that the passive film has the characteristics of valve metal in respect of capacitance and formation potential, and consists of two types of grains on the surface.