Oxidation Behavior of a High-Nb-Containing TiAl Alloy with Multilayered Thermal Barrier Coatings
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Oxidation Behavior of a High-Nb-Containing TiAl Alloy with Multilayered Thermal Barrier Coatings Kun Zhang1 • Tiebang Zhang1 • Lin Song1
Submitted: 16 April 2018 / in revised form: 21 June 2018 ASM International 2018
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. Keywords air plasma spraying multilayered thermal barrier coatings oxidation resistance TiAl alloy
& Tiebang Zhang [email protected] 1
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China
Introduction In recent years, TiAl alloys have attracted an increasing attention in high-temperature applications due to their attractive combination of low density and excellent hightemperature strength and creep properties, etc. (Ref 1-3). As advanced structural materials, TiAl alloys exhibit considerable potential for high-temperature applications in aerospace, automotive and power generation industries (Ref 4, 5). However, when exposed in air at elevated temperatures for a long time, TiAl alloys exhibit a poor oxidation resistance and a deterioration of mechanical properties. The oxidation resistance of TiAl alloys decreases rapidly at temperatures above 750 C due to the formation of fast-growing TiO2 (Ref 6, 7). What is more, TiAl alloys always suffer a reduction in ductility following high-temperature exposure in air, which has been shown to be a result of near-surface microstructural changes owning to diffusion of oxygen into the near-surface region (Ref 8, 9). Over the past several years, substantial efforts have been made to improve the oxidation resistance and mechanical properties of TiAl alloys. Alloying and surface modification are two main methods, which have been widely u
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