Microstructural characterization of YSZ-CoNiCrAlY two-layered thermal barrier coating formed on γ-TiAl intermetallic alloy via APS process

Abstract

With the aid of development in materials science in recent years, γ-TiAl alloys have been extensively utilized to reduce mass density and enhance mechanical characteristics of gas turbine blades used in the last stage of low pressure part. In the current study, the γ-TiAl alloy with chemical composition of Ti-48Al-2Nb–2Cr (at. %) is employed as the substrate material. Two different coatings including a single-layer coating applied via Co-based powder of AMDRY 995C [CoNiCrAlY] and a two-layered TBC coating consisted of a ceramic top coat of YSZ and a metallic bond coat of CoNiCrAlY using APS process at 2000°C. Microstructural analysis as well as the isothermal oxidation resistance of the both obtained coatings at 1050°C is investigated. For the two-layered TBC coating, it is demonstrated that the dominant compounds include ZrO2 oxide with a little amount of Y2O3 oxide. The presence of these oxides plays the essential role in high temperature oxidation resistance of the formed TBC coating on the γ-TiAl alloy. Furthermore, it is revealed that the best high temperature oxidation resistance is obtained by the two-layered TBC coating on the γ-TiAl substrate.