Effect of thermal oxidation on the corrosion resistance of Ti6Al4V alloy in hydrochloric and nitric acid medium

The characteristics of Ti6Al4V alloy subjected to thermal oxidation in air atmosphere at 650 degrees C for 48h and its corrosion behavior in 0.1 and 4M HCl and HNO3 medium are addressed. When compared to the naturally formed oxide layer (approximate to 4-6nm), a relatively thicker oxide scale (approximate to 7 mu m) is formed throughout the surface of Ti6Al4V alloy after thermal oxidation. XRD pattern disclose the formation of the rutile and oxygen-diffused titanium as the predominant phases. A significant improvement in the hardness (from 324 +/- 8 to 985 +/- 40 HV0.25) is observed due to the formation of hard oxide layer on the surface followed by the presence of an oxygen diffusion zone beneath it. Electrochemical studies reveal that the thermally oxidized Ti6Al4V alloy offers a better corrosion resistance than its untreated counterpart in both HCl and HNO3 medium. The uniform surface coverage, compactness and thickness of the oxide layer provide an effective barrier towards corrosion of the Ti6Al4V alloy. The study concludes that thermal oxidation is an effective approach to engineer the surface of Ti6Al4V alloy to increase its corrosion resistance in HCl and HNO3 medium.