Abstract
Oxidation of TiAl alloys has been recognized as an obstacle for high-temperature applications such as aero engine and gas turbine. Substantial efforts have been made to improve oxidation resistance of TiAl alloys at elevated temperatures. In this study, multilayered thermal barrier coatings are prepared to protect a high-Nb-containing TiAl alloy from oxidation by air plasma spraying. The combination of Al2O3-13wt.%TiO2 ceramic coatings and NiCoCrAlY metallic coatings can improve thermal stability and increase the service lifetime of coatings. The fully melted TiO2 particles distribute in ceramic coatings uniformly and act as sealing pores and microcracks, which decrease porosity of the ceramic coatings and reduce diffusion channels of oxygen atoms. The porosity of surface and cross-section morphology are 5.5 ± 0.8 and 5.1 ± 0.8%, respectively. The results of oxidation experiment carried out at 800 and 900 °C for 100 h indicate that the coatings can effectively protect a high-Nb-containing TiAl alloy from oxidation. The mass gain of the high-Nb-containing TiAl alloys with coatings is lower than that of the one without coatings. The ceramic coatings retard diffusion of large amount of oxygen atoms, and bond coatings avoid to be excessively oxidized. Thus, the multilayered thermal barrier coatings exhibit an excellent long-term stability.
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