Sol–gel Al2O3/ZrO2 duplex films for protection of a γ-TiAl based alloy against high temperature oxidation

Abstract

Al2O3/ZrO2 duplex films were deposited on a γ-TiAl based alloy by sol–gel processing starting from aluminum isopropoxide (Al(OC3H7)3) and zirconium (IV) oxychloride octahydrate (ZrOCl2 · 8H2O) as raw materials. Isothermal oxidation at 900 and 1,000 °C in 0.1 MPa O2 and cyclic oxidation at 1,000 °C in air of the coated and uncoated specimens were performed to investigate the effect of the duplex films on the oxidation behavior of the γ-TiAl alloy. The results of the isothermal oxidation tests indicated that the parabolic rate constants of the alloy were decreased due to the applied thin film. Additionally, the present film exhibited a beneficial effect on the cyclic oxidation resistance of the alloy in air. The duplex film could restrain the growth of TiO2, causing an increase of the Al2O3 content in the oxide mixture and thus decreased the oxidation rate.