Recession of an
EB‐ PVD YSZ Coated Turbine Blade by and CaSO4 , Fe ‐Rich
Ti CMAS‐Type Deposits
An in‐service high‐pressure turbine blade with a columnar,
‐stabilized Y2O3 ( ZrO2 YSZ) thermal barrier coating ( TBC)
fabricated by electron‐beam physical vapor deposition was investigated to access the TBC hot corrosion mechanisms during turbine operation. The TBC exhibits a through‐thickness pore filling with anhydrite‐type .
Chemical analysis of the CaSO4 CMAS‐type particle deposits reveals relatively low but high SiO2 contents and substantial amounts of CaO
and Fe2O3 . The hot corrosion scenario observed at the TiO2 YSZ column tips involves newly formed and the garnet‐type phase CaZrO3 ,
also known as the mineral kimzeyite. The phase relationships were confirmed in laboratory experiments. Ca3(Zr,Mg,Ti)2(Fe,Al,Si)3O12 as well as the particle deposits prove to be effective solvents for CaSO4 YSZ introducing distinct solid‐state
reactions. The results support the idea of a dual YSZ hot corrosion process. A first stage controlled by a ‐free SiO2 ‐source, most likely primary Ca
produces a thin CaSO4 layer. A second, CaZrO3 CMAS‐type stage providing high concentrations of , Fe2O3 ,
and TiO2 favors the formation of kimzeyite. The melting temperature of kimzeyite presumably defines a thermal operation limit for SiO2 YSZ‐based TBCs.
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Document Type: Research Article
Publication date: 2011-12-01