Delayed formation of thermally grown oxide in environmental barrier coatings for non-oxide ceramic matrix composites

The oxidation and corrosion behavior at elevated temperatures of a SiCF/SiC(N) composite with two environmental barrier coating (EBC) systems topcoat was studied. After both processes, the formation of a silica-based thermally grown oxide (TGO) layer was observed. The formation of this TGO caused two principal failure mechanisms of the EBC. Firstly, spallation of the EBC induced by stresses from volume expansion and phase transformation to crystalline SiO2 was observed. Water vapor corrosion of the TGO with gap formation in the top region of the TGO was found to be a second failure mechanism. The formation of the TGO could be controlled by introducing an additional intermediate layer based on Yb2Si2O7 filled with SiC particles. The SiC particles in the intermediate layer were oxidized and served as getter to reduce the permeation of oxidants (O2, H2O) into the material. In this way, the formation of the TGO and the failure mechanisms caused by their formation and growth could be significantly delayed.