In some technological areas, mechanical structures and components are exposed to high temperatures and environmental conditions that may lead to material degradation or damage. For example, certain mechanical structures and components associated with gas turbine engines are subjected to very high temperatures and harsh environmental conditions, particularly in the combustion section and at the turbine inlet section. Such structures and components include, but are not limited to, blades, vanes, blade tracks, and combustor liners. Improvements in efficiency and reductions in emissions have driven increased demands for higher gas turbine inlet temperatures, which in turn require technological improvements in cooling, materials, and coatings to achieve higher inlet temperatures. Due to intrinsic limitations in the material properties and performance characteristics of high temperature metallic materials such as Ni-based superalloys, emphasis has shifted to the use of next generation high temperature materials such as, for example, silicon-based ceramic materials.
Although silicon-based ceramic materials exhibit desirable high temperature mechanical, physical and chemical properties, such materials can suffer from rapid recession in combustion environments due to volatilization of silica scale by water vapor. Therefore, protective coatings are used to protect the silicon-based ceramics from volatilization caused by water vapor present in the hot combustion gases. Such coatings are commonly referred to as environmental barrier coatings (EBC).