Oxidation kinetics of the pack siliconized TiAl-based alloy and microstructure evolution of the coating

Abstract

The cyclic oxidation resistance of a two-phase TiAl-based alloy was remarkably improved with the formation of composite coating by siliconization with mixed powder of 15 wt%Si + 85 wt%Al 2O 3. The composite coating consists of a Ti 5Si 3-based inner layer and an Al 2O 3-based outer layer. The cyclic oxidation test at 900 °C showed that increasing the siliconization temperature benefits the oxidation resistance. The higher the siliconization temperature, the stabler the Ti 5Si 3-based layer and the more Al 2O 3 concentrated in the outer layer. Usually, the oxidation curves consist of three regions, the parabolic, the linear and the quadratic. For the specimen that was siliconized at 1250 °C for 2 h, however, only the parabolic region appeared during the whole cyclic oxidation test at 900 °C up to 1000 h. The weight gain is less than 0.3 mg cm −2 after cyclic oxidation at 900 °C for 1000 h, corresponding to a parabolic oxidation rate constant, K p ≈ 6.03 × 10 −5 mg 2/(cm 4 h). Such a low oxidation rate is attributed to the composite layer of the specimen with a stable Ti 5Si 3-based layer and a dense Al 2O 3-based layer.