Corrosion behaviour of Ti-4Al-4V alloy in nitric, phosphoric and sulfuric acid solutions at room temperature

Electron beam melting of Ti-6-4 scrap has been carried out. Aluminium losses were verified for all the runs and commercial-size ingots of Ti-4-4 alloy were obtained. Tensile tests and hardness measurements have shown that the Ti-4-4 alloy has mechanical strength close to the Ti-6-4 alloy as well as higher ductility. The corrosion behaviour of the Ti-4-4 alloy was investigated in HNO3, H3PO4 and H2SO4 solutions at room temperature. Ti-4-4 alloy is passive in all HNO3 solutions and in 20 wt% H3PO4 and presents an active behaviour in 40–80 wt% H3PO4 and in all H2SO4 solutions. Ti-4-4 alloy is highly corrosion resistant in HNO3 and 20 wt% H3PO4 and has a moderate resistance in 40 wt% H3PO4. Ti-4-4 alloy can be regarded as a potential candidate to replace CP–Ti in these media. In more concentrated H3PO4 solutions, and in H2SO4, very high corrosion rates were observed.