Abstract
Environmental barrier coatings (EBCs) are necessary for silicon carbide (SiC) fiber-reinforced SiC matrix (SiC/SiC) composites in the application for next-generation aircraft engines to prevent degradation of the composites. Since EBCs are multi-layered structure in which each layer fulfills an individual function, the mechanical state becomes complicated. Addition of a columnar structure layer on top, which is being considered to alleviate thermal shock, could make the mechanical state even more complicated. The purpose of this study is to ensure the mechanical stability of an EBC (Yb2SiO5 column/ gradient composition layers of Yb2SiO5 and Yb2Si2O7/mullite/SiAlON/SiC) subject to thermal stress by numerical simulation. We established a finite element method (FEM) model to determine the coating layer thicknesses to prevent cracks along mullite/SiAlON and SiAlON/SiC interfaces in the EBC for SiC/SiC substrate, where strong thermal stress occurs during cooling in fabrication process. The structural condition to prevent these interface crack initiations can be obtained by comparing ERRs, which are evaluated by FEM calculations with varying thicknesses of the mullite, SiAlON and SiC layers, and experimental fracture toughnesses of corresponding interfaces.
