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.