A Mathematical Model to Assess CMAS Damage in EBCs

As the power density of advanced engines increases, the need for new materials that are capable of higher operating temperatures, such as ceramic matrix composites (CMCs), is critical for turbine hot-section static and rotating components. Such advanced materials have demonstrated the promise to significantly increase the engine temperature capability relative to conventional super alloy metallic blades. They also show the potential to enable longer life, reduced emissions, growth margin, reduced weight and increased performance relative to super alloy blade materials. Environmental Barrier Coatings (EBCs) are required for SiC-based composites used in hot-section components of aircraft turbine engines to limit degradation from reaction of the composite with combustion gases. EBCs themselves are subject to degradation when debris composed of calcium-magnesium alumino-silicates (CMAS) is ingested into the engine melts in the turbine hot-section, and deposits on the coated components. The CMAS reacts with the coating and degrades the mechanical properties of the coating during temperature cycling which occurs during normal engine operation. Models linking the thermochemical and thermomechanical degradation of the EBCs due to CMAS are needed to understand life of the coatings and to identify best strategies for developing improved coating systems. MR&D is proposing a combined analytical and experimental program to develop a mathematical model for CMC EBCs exposed to CMAS.

NASA Glenn has been directly involved in the effort to bring these materials to turbine hot section components. The NASA Ultra Efficient Engine Technology program (UEET) was focused on driving the next generation of turbine engine technology. Currently, the Aeronautics Research Mission Directorate (ARMD) Thrust 3 for Ultra-Efficient Commercial Vehicles focuses on the development and demonstration of advanced high-temperature materials which are capable of surviving the extreme environments of turbine combustion and CMAS attack.

In the commercial sector, the Rolls Royce Trent 1000 and Trent XWB engines are being developed for the Boeing 787 and Airbus A350 XWB aircraft, respectively. The Trent 1000 was the launch engine for the Boeing 787. These are large markets where the benefit of this technology will have a lasting impact in efficiency and cost. By working closely with Rolls Royce during the early stages of this development program, MR&D has ensured that the resulting products will meet the requirements of future customers. Rolls Royce has expressed a serious interest in this technology and, as demonstrated above, has a sizable market for its application. The aerospace industry is not the only potential beneficiary of this technology. The Department of Defense (DoD) is working hard to improve environmental barrier coatings' resistance to CMAS attack. The proposed modeling effort could be used to both improve existing CMAS damage models for in-service components and to aid in the evaluation of new coatings exposed to a wide range of CMAS compositions.

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