The effect of water vapor on the oxidation behavior of γ-TiAl–Ag coatings at 1073 K in air

Oxidation exposures were carried out at 1073 K in air with different H2O contents for 100 h to assess the oxidation resistance of Ti–48Al–xAg (x=1, 2, 3 at.%) coatings. It has been found that both Ag content in the coating and H2O content in air have substantial influence on the oxidation behavior. For coatings with 1.0 at.% Ag, TiO2 and the mixture of TiO2+Al2O3 were formed in 15.5 and 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 2.0 and 3.0 at.% Ag, higher H2O contents (15.5 and 30.8 vol.%) resulted in the formation of a duplex oxide scale, with a mixed layer of TiO2+Al2O3 on top of a continuous Al2O3 layer, while continuous single Al2O3 layers were 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. The coatings have shown good compatibility with the TiAl–10Cr substrates after the corrosion tests. No hard, brittle compounds were observed at the coating/substrate interface.