Effect of TEBC on the Performance of Al2O3/Al2O3 Ceramic Matrix Composites

Abstract

State-of-the art oxide-oxide ceramic matrix composites (CMC) based on Al2O3 fibers and porous Al2O3 matrices and are developed for various applications in harsh environments such as combustion atmospheres. Thermal-chemical degradation of such CMC includes fiber grain growth, matrix densification, fiber-matrix sintering, surface reactions with mineral dusts or molten salts, and hydroxylation/volatilization of Si- or Al-hydroxide species. Additionally, the relatively weak porous oxide matrices make CMC surfaces prone to surface erosion e.g. in high velocity gas flows or mechanical impact/abrasion. Low-thermal conductivity and environmentally stable protective oxide coatings promise effective thermal protection, improved chemical stability, reduced gas permeability, and erosion/abrasion resistance. As typical coating deposition processes are introducing additional thermal loads or surface chemical reactions, coatings may also significantly impact the CMC substrate. The effect of coatings on the overall performance of coated Al2O3-Al2O3 CMC materials is discussed on the examples of slurry-based, reaction-bonded Al2O3 and APS Y2O3 coatings.