Selective Dissolution of Ti-6Al-4V Titanium Alloy in Mixed HCl + H2SO4 Solution

The effect of microstructure on the corrosion behavior of Ti-6Al-4V titanium alloy was investigated. Solution annealing at 1066 ^oC for 1 h followed by cooling at different media was applied to obtain different microstructure. The microstructure as well as the chemical composition changes after heat treatment was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Dual phase (α+β) microstructure was obtained regardless of cooling rate. However, the volume fraction and the grain size of α phase decreased with increasing cooling rate. Furthermore, the chemical composition in either α or β phase also varied with cooling rate. The stability of passive film formed in 1 M HCl + 0.5 M H₂SO₄ mixed solution was investigated by conducting potential decay measurement and Auger electron spectroscopy (AES). At open circuit potential, selective dissolution of vanadium-depleted α phase in 1 M HCl + 0.5 M H₂SO₄ mixed solution was found. The possible reason for the occurrence of selective dissolution was discussed by examining the electrochemical properties of the respective phases.