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. EBC is fabricated by depositing several layers on SiC/SiC composite and cooling it to room temperature. During the cooling process, creep appears to occur due to the slow cooling rate. The purpose of this study is to ensure the mechanical stability of EBC model (Yb2SiO5 column/ gradient composition layers of Yb2SiO5 and Yb2Si2O7/mullite/SiAlON/SiC) subject to thermal stress considering creep by numerical simulation. We conducted thermal stress finite element method (FEM) analysis to predict energy release rates (ERRs) for mullite/SiAlON and SiAlON/SiC interface crack initiations and investigate the effect of creep on ERRs. The result reveals that ERRs are decreased by stress relaxation due to creep. We also evaluated ERRs for these interface crack initiations with varying thicknesses of the mullite, SiAlON and SiC layers by FEM calculations to obtain the dependence of layer thicknesses on ERRs.
