The effect of porosity, mixed molecular/Knudsen diffusion, and a surface barrier layer on steam corrosion of Yb2Si2O7

Yb2Si2O7 is a promising candidate environmental barrier coating (EBCs) for ceramic aero-engine components. The effect of microstructure, especially porosity, on steam corrosion of Yb2Si2O7 was studied for sintered compacts of different porosities at 1350 degrees C. A porous layer of Yb2SiO5 formed on the surface, with the level of porosity determining corrosion rate independent of grain size. Mixed molecular/Knudsen diffusion significantly reduced effective gaseous diffusion through the pores. A thin deposit of dense Yb3Al5O12 on the surface offered protection from corrosion suggesting that microstructural control of pore formation and the inclusion of Al2O3 in Yb2Si2O7 coatings can have significant beneficial effects steam corrosion resistance of EBCs.