Improved high temperature oxidation resistance of TiAl alloy by pack cementation Al2O3/Ti5Si3 composite coating with sandwich structure

TiAl alloys are highly promising for aerospace applications due to their low density and high specific strength. However, their insufficient high-temperature oxidation resistance poses a significant limitation to widespread practical use. To address this, a TiAl substrate was embedded in an Al 2 O 3 -SiO 2 powder mixture and subjected to a diffusion-based pack cementation process at 1000 °C for 5 h under vacuum. This process produced a sandwich-structured Al 2 O 3 /Ti 5 Si 3 composite coating, with continuous Ti 5 Si 3 inner/outer layers separated by a middle Al 2 O 3 layer. During cyclic oxidation at 900 °C for 100 h, the coated alloy showed a significantly lower weight gain (2.38 mg/cm 2 ) than the uncoated alloy (10.76 mg/cm 2 ), representing a ∼77 % reduction. The enhanced protection stems from the ability of the Ti 5 Si 3 and Al 2 O 3 layers to act as a dual barrier, effectively blocking inward oxygen diffusion and outward migration of Ti/Al cations. In addition, the Al 2 O 3 formed by oxidation of the substrate itself further suppresses the inward diffusion of oxygen, thereby substantially improving the high-temperature oxidation resistance of the TiAl alloy.