Abstract
Ytterbium silicate coatings were deposited on SiCf/SiC ceramics matrix composite (CMC) substrates by plasma spray-physical vapor deposition (PS-PVD), and the microstructures and phase constituents of the coatings were studied. The results show that the Yb2SiO5 coating prepared with high power and low pressure (65 kW/2 mbar) had quasi-columnar structure, mainly deposited from the vapor phase, whereas the coating prepared with low power and high pressure (40 kW/10 mbar) had a typical layered structure, mainly deposited from the liquid phase. The deposition efficiency of parameter A (~2 μm/min) was also significantly lower than that of parameter B (~20 μm/min). After annealing at 1300 °C for 20 h, the coating prepared by 65 kW/2 mbar was mainly composed of ytterbium disilicate phase (77.2 wt %). The coating also contained some silicon-rich phase. The coating prepared by 40 kW/10 mbar basically consisted of ytterbium monosilicate (63.6 wt %). In addition, a small amount of silicon-rich phase and ytterbium-rich phase were also present in the coating. Accompanied with calculation results by the FactSage software, the cause of deviations in phase compositions was analyzed.
Highlights
In order to meet the service requirements of next-generation aircraft engines with a high thrust-to-weight ratio, the application of ceramic matrix composites (CMCs) to thermal structural parts of engines is being increasingly considered for replacing the existing superalloys [1,2]
The top ceramic layer is mainly used to block the entry of water vapor, and the mullite layer can reduce the mismatch of coefficients of thermal expansion (CTEs) and alleviate thermal
Ytterbium silicate coatings were prepared by plasma spray-physical vapor deposition (PS-PVD) and the microstructure and phase constituents of the coatings before and after annealing were studied
Summary
In order to meet the service requirements of next-generation aircraft engines with a high thrust-to-weight ratio, the application of ceramic matrix composites (CMCs) to thermal structural parts of engines is being increasingly considered for replacing the existing superalloys [1,2]. Once CMCs are exposed to fast-flowing water-vapor-rich gasses, silicon oxide reacts with water vapor, forming gaseous silicon hydroxide and causing degradation of CMC components [3]. This reaction results in a serious drop in the thermal and mechanical properties of the CMCs. A protective coating on the surface of the CMCs (namely, an environmental barrier coating, EBC), is necessary to protect CMCs from environmental corrosion and improve both the service life and service temperature of CMCs [4]. Through many years of development, EBCs have evolved from the first single-layer of mullite to the advanced three-layer structure, including Si/mullite/rare earth silicate [5,6]. The top ceramic layer (rare earth silicate) is mainly used to block the entry of water vapor, and the mullite layer can reduce the mismatch of coefficients of thermal expansion (CTEs) and alleviate thermal
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