Protective pre‐deposited slurry dip‐coating alumina layer on TBC system

In the present study, a thin intermediate protective α‐alumina layer was pre‐deposited by slurry dip‐coating technique on APS–CoNiCrAlY bond coat prior depositing APS–YSZ as top coat. The alumina layer acts as barrier for oxygen diffusion to protect the metallic bond coat from excessive oxidation. T...

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Bibliographic Details
Published in:Materials and corrosion 2017-07, Vol.68 (7), p.740-747
Main Authors: Abdeldaim, Hesham, Mahallawy, N. El
Format: Article
Language:English
Subjects:
Al2O3 intermediate protective layer
Aluminum oxide
Chromium oxides
Cracks
Diffusion barriers
Diffusion layers
Diffusion welding
Dip coatings
Image analysis
Immersion coating
Microscopy
Mixed oxides
Nickel base alloys
Oxidation
Protective coatings
Slurries
slurry dip‐coating technique
Spectroscopic analysis
thermal barrier coating
Thermal cycling
thermal cycling behavior
Thickness
Yttria-stabilized zirconia
α‐Al2O3 thermally grown oxide layer
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Summary:In the present study, a thin intermediate protective α‐alumina layer was pre‐deposited by slurry dip‐coating technique on APS–CoNiCrAlY bond coat prior depositing APS–YSZ as top coat. The alumina layer acts as barrier for oxygen diffusion to protect the metallic bond coat from excessive oxidation. The new TBC was compared with the standard TBC system which comprises of Ni‐superalloy substrate, CoNiCrAlY bond coat and YSZ top coat concerning the behavior under thermal cycling at 1150 °C. The samples were investigated before and after thermal cycling by optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive X‐ray spectroscopy (EDS), and X‐ray diffraction analysis (XRD). Image analysis was used to compare between the microstructure by measuring the crack lengths and the thermally grown oxide layer (TGO) average thickness after thermal cycling. It was observed that a more uniform and compact α‐Al2O3 TGO was formed in the new TBC system after thermal cycling comparing to the commercial one. It was, also, found that the alumina intermediate layer has the potential to reduce the length of the cracks and the average thickness of TGO by suppressing the detrimental mixed oxides, like Cr2O3, CoO, NiO, and (Ni, Co)(Cr, Al)2O4, thus, improving the TBC durability. A thin intermediate protective α‐alumina layer was pre‐deposited by slurry dip‐coating technique on APS‐CoNiCrAlY bond coat prior depositing APS–YSZ as top coat. The alumina layer acts as barrier for oxygen diffusion to protect the metallic bond coat from excessive oxidation. The new TBC was compared with the standard TBC system which comprises of Ni‐superalloy substrate, CoNiCrAlY bond coat and YSZ top coat.
ISSN:0947-5117
1521-4176
DOI:10.1002/maco.201609265