Environmental Barrier Coatings for Gas Turbine Application: Processing and Testing

Environmental barrier coatings (EBCs) are developed for advanced gas turbines primarily to eliminate rapid volatilization of hot-section SiC/SiC ceramic matrix composite (CMC) components in the water vapor rich environment as well as to inhibit their oxidation. There are various difficulties with accelerated lifetime testing of EBCs, i.e. to simulate the testing environment with high-velocity water vapor flow and thermal gradient through the sample during thermal cycling. Furthermore, processing of EBCs is known to be complicated due to re-crystallization and secondary phase issues in silicate coatings. Therefore, a burner rig test facility in Jülich, IEK-1 was modified and various EBC systems deposited with different processing routes, namely APS (atmospheric plasma spraying), HVOF (high-velocity oxy-fuel), VLPPS (very low-pressure plasma spraying) on SiC/SiC CMCs were tested. In this paper, these test results will be presented and degradation mechanisms will be discussed in relation to microstructure and phase composition of different coating systems.