Thermal Shock Behavior of Environment Barrier Coatings in a Calcium/Magnesium-Included Water Vapour Condition.

Environment Barrier Coatings (EBCs) working in real service process meet not only environment of high-temperature water vapour, but also face of calcium and magnesium corrosion. In this paper, EBCs made by plasma spray with Yb2Si2O7 coatings were tested by thermal shock in a calcium/magnesium-included water vapour environment at 1 250 °C for 300 cycles. The results showed that there formed two-layer corrosion structures at the coating surface. The topmost layer sustained calcium corrosion, forming obvious multi-phase structure with large pores with phases of (Yb/Ca)2 Si2 O7, (Yb/Ca)2 SiO5 and (Ca/Yb)2 SiO4. The subsurface layer sustained both calcium and magnesium corrosion but mainly the magnesium corrosion, also forming multi phases (Yb/Mg/Ca)2SiO5 and (Mg/Ca/Yb)2SiO4 with relatively dense structure. Via analyses on surface morphology, cross section microstructure, micro-EDS composition and XRD phase structures, the chemical reaction mechanism of the EBC coatings was studied under the calcium/magnesium-included water-vapour thermal shock environment, and the failure mechanism of the coating was provided. [ABSTRACT FROM AUTHOR]