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Recession of an EB ‐ PVD YSZ Coated Turbine Blade by CaSO 4 and Fe , Ti ‐Rich CMAS ‐Type Deposits
Author(s) -
Braue Wolfgang,
Mechnich Peter
Publication year - 2011
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2011.04747.x
Subject(s) - materials science , yttria stabilized zirconia , thermal barrier coating , chemical vapor deposition , particle (ecology) , corrosion , phase (matter) , chemical engineering , coating , composite material , metallurgy , mineralogy , nanotechnology , chemistry , cubic zirconia , geology , ceramic , organic chemistry , engineering , oceanography
An in‐service high‐pressure turbine blade with a columnar, Y 2 O 3 ‐stabilized ZrO 2 ( 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 CaSO 4 . Chemical analysis of the CMAS ‐type particle deposits reveals relatively low SiO 2 but high CaO contents and substantial amounts of Fe 2 O 3 and TiO 2 . The hot corrosion scenario observed at the YSZ column tips involves newly formed CaZrO 3 and the garnet‐type phase Ca 3 (Zr,Mg,Ti) 2 (Fe,Al,Si) 3 O 12 , also known as the mineral kimzeyite. The phase relationships were confirmed in laboratory experiments. CaSO 4 as well as the particle deposits prove to be effective solvents for YSZ introducing distinct solid‐state reactions. The results support the idea of a dual YSZ hot corrosion process. A first stage controlled by a SiO 2 ‐free Ca ‐source, most likely primary CaSO 4 produces a thin CaZrO 3 layer. A second, CMAS ‐type stage providing high concentrations of Fe 2 O 3 , TiO 2 , and SiO 2 favors the formation of kimzeyite. The melting temperature of kimzeyite presumably defines a thermal operation limit for YSZ ‐based TBCs .