Environmental durability of slurry based mullite–gadolinium silicate EBCs on silicon carbide

Water vapor oxidation and salt corrosion resistances of mullite–gadolinium silicate (Gd2SiO5) environmental barrier coatings (EBCs) dip coated on α-SiC substrates and sintered to 1430 °C/3 h in air were investigated. The EBC exhibited excellent adherence to the substrate during thermal cycling between 1350 °C and room temperature (RT) for 100 h in a simulated lean combustion environment (90% H2O–balance O2),11, 13 and 15 forming ∼10 μm porous silica layer at coating-substrate interface, compared to ∼17 μm for uncoated α-SiC exposed under same conditions. The EBC did not spall after a 24 h 1200 °C exposure in Na2SO4 corrosion environment leading to further coat densification. However, after 48 h salt exposure, the EBC showed severe through-thickness cracks, and cavities and de-lamination at coating-substrate interface. The corrosion gaseous products such as CO2, CO and SO2 trapped under a low viscosity glassy (Na2O·x(SiO2)) liquid phase were formed due to salt vapor reaction with α-SiC substrate created these cavities.