Innovative, Multifunctional Layered Coatings for High Temperature Ceramic Matrix Composites

The design and realization of thermal/environmental barrier coatings systems for the protection and insulation of ceramic matrix composites that can withstand combustion temperatures approaching 3100 Fahrenheit is a formidable challenge. But that is necessary for achieving 65% efficiency target in future combined-cycle gas-turbine engines. A multifaceted research program is proposed to address this challenge squarely. At the core of the proposed program is an innovative three-pronged approach that builds on our vast collective/collaborative experience in this area. Approach 1 entails multilayer, multifunctional plasma-sprayed coating system comprising different embodiments of thermal barrier coatings, environmental barrier coatings, and bond-coat. The materials and microstructures in each of these layers are rationally designed and selected to meet the afore-stated requirements. In Approach 2, dense plasma-sprayed coatings of newly designed ceramics with unprecedentedly low thermal conductivity will be used to combine both thermal-barrier and environmental-barrier functions in a single material for the first time. The hybrid Approach 3 combines Approaches 1 and 2 into one, where the thermal-barrier layer and the new low-thermal conductivity environmental-barrier layer are combined for synergistic benefits. Some redundancies and well thought out risk-mitigation strategies are built-in in the proposed program to ensure its success. The materials design will be guided by model experiments on sintered ceramic pellets, and the design of the multilayer, multifunctional architecture design will be informed by a thermo-mechanical modeling effort that can anticipate failures and their locations under aggressive thermal loading (thermal gradient) and excursions that are expected in these systems, enabling optimal design strategies. The deposition of multi-layer coatings of different materials will be guided by in situ diagnostics and process- modeling protocol pioneered by our team. The suite of process parameters that emerge from this effort will be used to achieve programmed plasma-sprayed coatings with target compositions, phases, microstructures, and other characteristics. The resulting coatings will be characterized, and their performance will be evaluated, results from which will be fed back into the models iteratively to create a fine-tuned coatings solution for future commercialization. In Phase I of the proposed program, the initial feasibility of the three-pronged approach will be demonstrated, working closely with key partners including government, an engine manufacturer, and a coatings company. The Phase I effort will establish a framework for full scale development in Phase II and beyond.