Challenges of Testing EB Coated CMC under SPLCF Conditions in Steam Environment at High Temperatures

Environmental barrier (EB) coated monolithic SiC (Hexoloy) and 3D woven SiC/SiC composite specimens were tested under sustained peak low cycle fatigue (SPLCF) conditions at 1204°C at 69 MPa (maximum stress) in steam environment up to 200hrs. Both types of specimens were coated with a multilayer EB coating (Mullite + rare earth disilicate (RED) bond coat and RED top coat) by slurry method. The coated Hexoloy specimen survived 200hrs testing of testing, but the coating showed through-the-thickness cracks and delamination. In contrast, the coated 3D woven SiC/SiC composite specimens failed between 48 and 160 hrs and showed extensive damage in the coating as well as within the CMC substrate.