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

Al(2)O(3)/ZrO(2) duplex films were deposited on a gamma-TiAl based alloy by sol-gel processing starting from aluminum isopropoxide (Al(OC(3)H(7))(3)) and zirconium (IV) oxychloride octahydrate (ZrOCl(2) center dot 8H(2)O) as raw materials. Isothermal oxidation at 900 and 1,000 degrees C in 0.1 MPa O(2) and cyclic oxidation at 1,000 degrees 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 gamma-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 TiO(2), causing an increase of the Al(2)O(3) content in the oxide mixture and thus decreased the oxidation rate.