Novel Processing Approaches for Advanced Thermal / Environmental Barrier Coatings

Lightweight silicon-based ceramics are leading candidates to replace heavier nickel-based superalloys for use on hot section components in next generation gas turbine engines having increased specific power.  However, exposures of these materials to the high temperatures, pressures and velocities of water vapor containing combustion environments alter the effectiveness of thermally grown silica scales in protecting the ceramic components from oxidation and component recession during service. To limit this drawback, environmental barrier coatings (EBCs) are required that protect the underlying ceramic substrate from environmental attack. Such coatings require good stability in the presence of water vapor, a mechanism for limiting the transport of oxygen and water vapor to the ceramic substrate, good chemical compatibility at the interface of unlike materials, high temperature phase stability to limit volume changes resulting from phase transformations in the coating materials and the ability to provide thermal and erosion protection. The ongoing drive to promote higher temperature protection and prime reliant performance of these systems has led to interest in advanced thermal/environmental barrier coating (T/EBC) systems having enhanced performance over current state-of-the-art T/EBC systems (based on silicon / mullite + barium strontium aluminosilicate (BSAS) / BSAS). In this work, novel coating synthesis techniques that enable the deposition of multilayered T/EBC’s anticipated to have higher temperature capability and improved durability over of current systems have been investigated. The effect of processing variables on the microstructure of T/EBC layers will be discussed, along with the effect of coating composition, microstructure and architecture on the performance of T/EBC systems in high temperature, water vapor containing environments.