The effect of water vapor on the oxidation behavior of γ-TiAl-Ag coatings at 800°C in air

Oxidation exposures were carried out to assess the oxidation resistance of Ti-48Al-xAg (x = 1 and 3 at.%) coatings at 800degreesC in air with different H2O contents for 100 hours. The coatings containing 3.0 at.% Ag have been proved to be resistant against oxidation attacks in wet air. It has been found that both Ag content in the coating and H2O content in the atmosphere have substantial influence on the oxidation behavior. For coatings with 1.0 at.% Ag, TiO2 and mixed TiO2 + Al2O3 were formed in 30.8 vol.%H2O, while TiO2, the mixture of TiO2 + Al2O3 and continuous Al2O3 layers were formed in 9.0 vol.% H2O. For the coatings containing 3.0 at.% Ag, higher H2O content (30.8 vol.%) resulted in the formation of duplex oxide scale with a mixture of TiO2 + Al2O3 on top of continuous Al2O3, while continuous single Al2O3 layer was formed in lower H2O content (9.0 vol.%). The effect of H2O vapor on the oxidation behavior was explained by the interaction of H2O and TiO2, or the rapid and anisotropic diffusion of hydrogen in TiO2 during oxidation.