Enhancing the high-temperature oxidation resistance of TiAl alloy via a novel Al2O3/Ti5Si3 composite coating prepared through a modified pack cementation technique

Abstract

TiAl alloys, known for their low density and high strength, are used as structural components in aircraft engines at high temperatures. Considering the high-temperature application environment, their oxidation resistance becomes an essential requirement. In this study, Ti-48Al-2Cr-2Nb alloy was buried in SiO₂ powder and heat-treated at 1000 °C for 5 h under vacuum circumstance. After diffusion reaction, an ∼ 3 μm thick Al₂O₃/Ti₅Si₃ composite coating was successfully fabricated on the alloy surface. This novel coating was composed of a continuous Ti₅Si₃ layer and discontinuous Al₂O₃ layers surrounded by Ti₅Si₃. After 100 h oxidation, the mass gain of the coated sample was only 2.93 mg·cm⁻², significantly lower than the 10.30 mg·cm⁻² for the uncoated TiAl alloys. The higher oxidation temperature of the Ti₅Si₃ surface layer contributed to the excellent high-temperature oxidation resistance of the composite coating. Additionally, the formation of Al₂O₃ and SiO₂ during oxidation and the presence of the discontinuous Al₂O₃ layers within the coating reduced the effective cross-sectional area for elemental diffusion, thereby delaying the inward diffusion of O and further enhancing the oxidation resistance.