A coupled theory for deformation and phase transformation due to CMAS infiltration and corrosion of thermal barrier coatings

The failure behavior of thermal barrier coatings (TBCs) involves multilayered systems infiltrated with calcium–magnesium–alumino-silicates (CMAS). The metastable tetragonal phase is mainly composed of 7YSZ (7 mol.% Y2O3-stabilized ZrO2), and it destabilizes into the Y-lean tetragonal phase, which may be induced by CMAS infiltration, and transforms into a monoclinic phase during cooling. The phase transformation leads to volume expansion around the CMAS-rich layer. Furthermore, it is shown that the spalling of the coating system emerges when the surface of the coating system is subjected to significant residual stress. In this study, a double-cantilever beam model is established to describe the macroscopic phenomenon of thermal buckling induced via CMAS. The result of the buckle height is used to demonstrate the consistency of the experiment and finite element simulation. The experimental parameters are imported into a multilayer cantilever beam model to analyze the interfacial stresses due to CMAS infiltration. The finite element results indicate that the phase transformation leads to damage in the coating system wherein the interfacial stresses due to phase transformation are 27% higher than those in the model without phase transformation.

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Characterization of thermal barrier coatings formed by electon-beam physical vapor deposition (EB-PVD)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010015410x ◽

1989 ◽

Vol 47 ◽

pp. 426-427

Author(s):

Ozer Unal

Keyword(s):

Thermal Barrier Coatings ◽

Physical Vapor Deposition ◽

Ceramic Coating ◽

High Vacuum ◽

Ceramic Coatings ◽

High Energy ◽

Thermal Barrier ◽

Protective Oxide ◽

Barrier Coatings ◽

Energy Beam

Interest in ceramics as thermal barrier coatings for hot components of turbine engines has increased rapidly over the last decade. The primary reason for this is the significant reduction in heat load and increased chemical inertness against corrosive species with the ceramic coating materials. Among other candidates, partially-stabilized zirconia is the focus of attention mainly because ot its low thermal conductivity and high thermal expansion coefficient.The coatings were made by Garrett Turbine Engine Company. Ni-base super-alloy was used as the substrate and later a bond-coating with high Al activity was formed over it. The ceramic coatings, with a thickness of about 50 μm, were formed by EB-PVD in a high-vacuum chamber by heating the target material (ZrO2-20 w/0 Y2O3) above its evaporation temperaturef >3500 °C) with a high-energy beam and condensing the resulting vapor onto a rotating heated substrate. A heat treatment in an oxidizing environment was performed later on to form a protective oxide layer to improve the adhesion between the ceramic coating and substrate. Bulk samples were studied by utilizing a Scintag diffractometer and a JEOL JXA-840 SEM; examinations of cross-sectional thin-films of the interface region were performed in a Philips CM 30 TEM operating at 300 kV and for chemical analysis a KEVEX X-ray spectrometer (EDS) was used.

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Delamination of Electron-Beam Physical-Vapor Deposition Thermal Barrier Coatings using Luminescent Layers

AIAA Scitech 2021 Forum ◽

10.2514/6.2021-0432 ◽

2021 ◽

Author(s):

Quentin P. Fouliard ◽

Ranajay Ghosh ◽

Seetha Raghavan

Keyword(s):

Electron Beam ◽

Thermal Barrier Coatings ◽

Vapor Deposition ◽

Physical Vapor Deposition ◽

Thermal Barrier ◽

Barrier Coatings

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