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Stresses and Microstructural Development of Thermal Barrier Coatings Using AIP/D‐gun Two‐Step Processing
Author(s) -
Ke Peiling,
Wang Qimin,
Hua Weigang,
Gong Jun,
Sun Chao,
Zhou Yanchun
Publication year - 2007
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.1551-2916.2007.01496.x
Subject(s) - materials science , thermal barrier coating , spallation , composite material , yttria stabilized zirconia , coalescence (physics) , superalloy , ceramic , nucleation , temperature cycling , alloy , thermal , cubic zirconia , chemistry , physics , organic chemistry , quantum mechanics , astrobiology , neutron , meteorology
After depositing a Ni–32Co–20Cr–8Al–0.5Y–1Si–0.03B (wt%) bond coat on a Ni‐base superalloy using arc ion plating (AIP), a ceramic top coat with hollow spherical powder of ZrO 2 –8 wt%Y 2 O 3 (HSP–YSZ) was deposited using detonation gun (D‐gun) spraying. Thermal exposure behaviors of thermal barrier coatings (TBCs) were investigated at 1100°C. The thermal growth oxides (TGO) layer thickened and became more undulated during thermal exposure. Yttrium aluminum garnet (YAG) was observed within TGO, which produced thickness imperfections and thus aided to build up out‐of‐plane stresses. As a result, radial cracks initiated at the defects around TGO imperfections and separation developed through crack nucleation, propagation, and coalescence at the weaker TGO/bond coat interface. With further thermal exposure, coalescence of interfacial separations created a connected crack. The TBC detached and final failure occurred at the TGO/bond coat interface, leading to spallation of TBC when cooling to ambient. The stress distributions in the TGO layer with different thermal exposure times were also measured using luminescence spectroscopy. The stresses were independent of time after a transient period from θ‐Al 2 O 3 to α‐Al 2 O 3 scale. It is suggested that the lifetime of AIP/D‐gun TBCs with an HSP–YSZ coat is controlled by the initiation and linking of a sub‐critical interfacial crack.