High temperature oxidation resistance of Ti-5553 alloy with electro-deposited SiO2 coating

Ti–5Al–5V–5Mo–3Cr (Ti-5553) metastable β titanium alloy possesses excellent high temperature mechanical properties, however, the oxidation resistance is fairly poor. In this work, a SiO2 coating was prepared on Ti-5553 alloy by cathodic electro-deposition. The high temperature oxidation resistance of the deposited SiO2 coating was evaluated at 800 °C. The results show that the optimal current density of deposition is −2.0 mA/cm2 for 300 s, and the thickness of the compact SiO2 film reaches 5.5 μm. The SiO2 film can react with Ti-5553 substrate and form protective Ti5Si3 layer, which inhibits the inward diffusion of oxygen from air, leading to the remarkable improvement of oxidation resistance. The mass gain is only 1.13 mg/cm2 after oxidation at 800 °C for 80 h. The oxide scale consists of TiO2, Al2O3, V2O5, Cr2O3 and SiO2, but Mo2O5 is absent. The occurrence of Kirkendall voids as well as the cracks induced by internal stress should be responsible for the deterioration of oxidation resistance, which may provide extra channels for oxygen diffusion inwards the substrate.