Environmental barrier coatings on alumina-reinforced CMCs: Experimental validation and numerical modeling of thermal stability

Recent advancements in ceramic matrix composites (CMCs), including SiC/SiC, C/SiC, C/C, Al 2 O 3 reinforced Al 2 O 3 , face various challenges at high temperature applications, including grain growth, sintering, and creep deformation which are leading to strength loss. The new generation of Environmental Barrier Coatings (EBCs) must allow the protection of these CMCs when operating under harsh conditions, which can reach up to 1100 °C in some applications, such as gas turbines and certain reforming processes. In this work, 8 wt% yttria stabilized zirconia (8YSZ) applied by Atmospheric Plasma Spraying (APS) on top of a porous alumina oxide matrix with reinforced alumina fibers Al 2 O 3 /Al 2 O 3 -CMC (OCMC), considering different interfaces, has been studied. Surface morphology and pre-treatment of CMCs is the most challenging part for thermal spray applications. Hence, two different surface structure were used in this work. The results show that the roughness of OCMC can be reduced from Rz = 41.8 ± 6.8 μm to 20.3 ± 1.1 μm with the new porous bond coat and plasma sprayed coating, resulting in a homogeneous surface morphology.. In terms of thermal stability, a numerical model that combines Object Oriented FEM (OOF) and Cohesive Zone Model CZM tools, has been developed to evaluate the effect of the porosity of the real microstructure and the characteristics of the interfacial roughness profile, respectively, in CMC/EBC structures. In addition, other materials, such as La 2 Zr 2 O 7 and Y 2 O 3 , have been numerically studied in order to evaluate their suitability as EBC. • Two different surface preparations are applied to the OCMC/EBC interface: structured by peel ply fiber and alumina porous coating (APO) • APO enables a better adhesion of EBC and homogenous coating • A numerical model based on the combination of OOF and CZM tools was developed to evaluate both surface preparations in terms of interfacial and mechanical properties • The mechanisms of crack propagation in OCMC/EBC systems were predicted by analysing the numerical results • The APO layer acts as a bond coat that improves adhesion and reduces the thermal stresses due to its porous structure