High temperature oxidation behaviour of Al2O3/Al composite coating on γ-TiAl

An Al2O3/Al composite coating was introduced on the substrate gamma-TiAl alloy by magnetron sputtering. The isothermal oxidation behaviour of the coated gamma-TiAl alloy was investigated at 1000 degrees C. The results suggested that the Al2O3/Al composite coating improved the oxidation resistance of gamma-TiAl alloy at 1000 degrees C air exposure. No spallation or crack was observed in the oxide scale of coated specimen, which was composed of alpha-Al2O3 and TiAl3 after the oxidation test. The outward Al diffusion from interlayer provided sufficient Al source for the formation of Al2O3 layer in the coating surface during the high temperature oxidation test. As an active intermetallic element with Ti, Al suppressed the outward of Ti effectively due to the formation of Ti-Al intermetallics. Owing to inward and outward diffusion, the Al interlayer was consumed after 100 h oxidation test and a Ti-Al interdiffusion zone was formed, which was beneficial for the adhesion between coating and substrate.