Development of an environmental barrier coating to mitigate CMAS attack

Gas turbine engines rely on Thermal Barrier Coatings (TBCs) to protect the high pressure turbine blades from high operating temperatures. Engine effciency and fuel consumption improve with increasing Turbine Inlet Temperature(TET). Therefore, a constantly rising TET has been observed during the last decades. However, any further increase is hindered by the presence of molten deposits of calcia-magnesia-alumina-silicates (CMAS), which is present in sand, dust, runway debris and volcanic ash. CMAS, characterized by a low melting temperature and excellent wettability, attacks the TBC. Mechanical and chemical degradation have been observed. This project studies the interaction between CMAS and Environmental Barrier Coatings (EBCs) doped with Rare Earths (REs). CMAS is expected to react with the EBC and to seal the TBC against any further attack. In the last years more attention has been given to REs in the incorporation into EBCs. Lanthanum, Gadolinium, Dysprosium and Ytterbium were identifed as being highly reactive with CMAS. In this work EBCs are produced via two novel routes: Sol-gel and Aerogel. These methods are cost effective and have a quick turnaround compared to Electron Beam Physical Vapour Deposition of RE-EBC; these properties make them ideal for research purpose. TBCs coated with an environmental barrier showed less damage compared with an uncoated sample. Production of new reaction material was observed in Dysprosium and Ytterbium doped sol-gel at higher atomic concentration. This reaction material forms on the top of the TBC columns, seals them and hinders the CMAS to infltrate.