Modeling of Thermal Stresses in Yttrium Aluminum Garnet and Alumina Fibers Coated with β″-Alumina

Since layered aluminate coatings such as β″-alumina are being considered for tailoring the interfacial properties of oxidation-resistant fiber-reinforced composites, stresses arising from thermal expansion mismatch were calculated for the substrate fiber and coating. Both isotropic and anisotropic β″-alumina coatings were analyzed for yttrium aluminum garnet and single crystal and polycrystalline alumina fibers. It was possible to rank the various fiber-coating combinations in terms of the magnitude of maximum tensile stresses present in the coating. Polycrystalline alumina + isotropic β″-alumina yielded the lowest tensile stresses with radial stress on the order of 10 MPa, while single crystal alumina + anisotropic β″-alumina yielded the highest tensile stresses with tangential stress on the order of >100 MPa.