Reactive Sputtered Ytterbium Silicate Environmental Barrier Coatings for Protection of Mo-Si-Based Alloys

The implementation of a structural material into the hot section of a turbine engine requires the protection against oxidation and water vapour. Since Mo-Si-based alloys do not provide this protection on their own over a long period of exposure time, the necessity for protective coatings becomes inevitable. Rare earth silicates, especially Yb-silicates, are known for their great potential to protect silica against water vapour recession and also for their oxidation protective behaviour due to their low silica reactivity. Reactive pulsed DC co-sputtering was investigated and used to produce a two-layered coating of Yb2Si2O7 and Yb2SiO5. The layers were implemented into a four-layered environmental barrier coating system combined with a bond coat consisting of a graded Mo-Si interlayer and a thin Si top layer intended to form slow-growing silica. The EBCs were tested up to 100 h at 1200 degrees C and 800 degrees C isothermally in air on top of three different Mo-Si-based alloys and show promise for oxidation protection. The pesting phenomenon was completely suppressed.