YSZ Environmental Barrier Coatings for Oxide/Oxide Ceramic Matrix Composites

Kurzfassung

Oxide/oxide ceramic matrix composites (CMCs) are considered key high-temperature materials for combustor liners, vanes or shrouds of next generation gas turbines. State-of-the-art oxide/oxide CMCs are prone to high-temperature recession in combustion environments caused by hydroxylation and subsequent volatilization of the constituents alumina and mullite. Therefore, CMC protection by suitable environmental barrier coatings (EBCs) is mandatory. Development and performance assessment of EBCs for oxide/oxide CMCs are focused topics at DLR since many years. EBC materials must exhibit superior corrosion stability with respect to alumina and mullite. But also compatibility between EBC and CMC substrate is mandatory. Among candidate EBC materials, yttria stabilized zirconia (YSZ) offers high corrosion resistance and adequate compatibility to alumina and mullite. YSZ-EBCs have been deposited on alumina/alumina CMCs by a variety of processes including electron beam physical vapor deposition (EB-PVD), air plasma spraying (APS) and metal-organic chemical vapor deposition (MOCVD). The different manufacturing processes for YSZ-EBCs are reviewed with regard to microstructure and microstructural stability. A common problem of YSZ coatings is their susceptibility against high-temperature corrosion induced by airborne inorganic particles, commonly referred as CMAS-type corrosion. CMAS-type corrosion of YSZ-coated oxide/oxide CMCs is discussed with respect to turbine target applications.