A novel CMAS‐resistant material based on thermodynamic equilibrium design: Apatite‐type Gd10(SiO4)6O3

Abstract

AbstractCalcium‐magnesium‐alumino‐silicates (CMAS) melt attack has been a critical issue for the thermal barrier coatings (TBCs) with ever‐increasing engine operating temperature. In this study, a novel CMAS‐resistant material apatite‐type Gd10(SiO4)6O3 is developed for TBCs application based on thermodynamic equilibrium design. The chemical reaction of Gd10(SiO4)6O3 bulk and CMAS melt is investigated at 1300°C. The CMAS corrosion resistance of Gd10(SiO4)6O3 bulk is evaluated and compared with the well‐studied CMAS‐resistant material Gd2Zr2O7 (GZO). It is found that Gd10(SiO4)6O3 shows a significantly enhanced CMAS resistance, including lower intrinsic CMAS infiltration rate (~1.09 μm/h1/2) and smaller infiltration upper limit (50‐62 μm) for a 20 mg/cm2 CMAS deposition. More importantly, for Gd10(SiO4)6O3, the CMAS infiltration only alters the composition but does not change the crystal structure or destroy microstructural integrity. The reaction mechanism is elucidated as following two stages: (a) surface Gd10(SiO4)6O3 quickly transforms into Ca2Gd8(SiO4)6O2 in suit by interdiffusion with CMAS melt and then is thermodynamically stable with CMAS melt, thereby effectively inhibiting the further CMAS infiltration and (b) with the ongoing interdiffusion of Gd/Ca, the CMAS‐infiltrated layer slowly thickens and follows a parabolic law. Meanwhile, the CMAS melt gradually precipitates Ca2Gd8(SiO4)6O2 and CaAl2Si2O8 (anorthite) until the melt is exhausted.