Abstract Scope |
Environmental barrier coatings (EBC) for ceramic matrix composites serve multiple functions in the turbine engine environment, providing resistance to high-temperature steam and calcium magnesium aluminosilicate (CMAS) molten deposits. Multicomponent rare earth silicates enable reductions in thermal conductivity as well as stabilization of nonequilibrium polymorphs, tailoring of EBC thermal expansion and thermochemical stability. In this presentation, the high temperature steam resistance of a two phase (Sc,Nd,Er,Yb,Lu)2Si2O7 material, the CMAS resistance of the single phase (Sc,Nd,Er,Yb,Lu)2SiO5 counterpart, and thermal conductivity of both the disilicate and monosilicate materials are presented. Choice of rare earth constituents with a wide mass and size range reduces thermal conductivity, small lanthanide rare earth silicates improve steam resistance, and large rare earths improve CMAS resistance. Thermal expansion is found to obey a rule of mixtures. Simultaneous optimization of multiple coating properties is demonstrated with this (Sc,Nd,Er,Yb,Lu) silicate mixture. |