Effect of Interfacial Roughness of Bond Coat on the Residual Adhesion Strength of a Plasma Sprayed TBC System after Thermal Cycle Fatigue(<Special Issue>Thermal Barrier Coating Systems for Gas Turbines)

Abstract The gas permeability of plasma sprayed yttria-stabilised zirconia coatings has been measured over a range of temperature, using hydrogen and oxygen gas. The permeability was found to be greater for coatings produced with longer stand-off distances, higher chamber pressures and lower torch powers. Porosity levels have been measured using densitometry and microstructural features have been examined using SEM. A model has been developed for prediction of the permeability from such microstructural features, based on percolation theory. Agreement between predicted and measured permeabilities is good. Ionic conduction through the coatings has also been briefly explored. It is concluded that transport of oxygen through the top coat in thermal barrier coating (TBC) systems, causing oxidation of the bond coat, occurs primarily by gas permeation rather than ionic conduction, at least up to temperatures of about 1000°C and probably up to higher temperatures. Top coat permeabilities appreciably below those measured will be required if the rate of bond coat oxidation is to be reduced by cutting the supply of oxygen to the interface.

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R&D Status and Needs for Improved EB-PVD Thermal Barrier Coating Performance

MRS Proceedings ◽

10.1557/proc-645-m10.1.1 ◽

2000 ◽

Vol 645 ◽

Cited By ~ 1

Author(s):

C. Leyens ◽

U. Schulz ◽

M. Bartsch ◽

M. Peters

Keyword(s):

Thermal Barrier Coating ◽

Bond Coat ◽

Gas Turbines ◽

Systems Approach ◽

Thermally Grown Oxide ◽

Thermal Barrier ◽

Factors Affecting ◽

Performance Improvements ◽

Barrier Coating ◽

Temperature Capability

ABSTRACTThe key issues for thermal barrier coating development are high temperature capability and durability under thermal cyclic conditions as experienced in the hot section of gas turbines. Due to the complexity of the system and the interaction of the constituents, performance improvements require a systems approach. However, there are issues closely related to the ceramic top coating and the bond coat, respectively. Reduced thermal conductivity, sintering, and stresses within the ceramic coating are addressed in the paper as well as factors affecting failure of the TBC by spallation. The latter is primarily governed by the formation and growth of the thermally grown oxide scale and therefore related to the bond coat. A strategy for lifetime assessment of TBCs is discussed.

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Shear Strength of a Thermal Barrier Coating Parallel to the Bond Coat

Journal of Engineering Materials and Technology ◽

10.1115/1.2806834 ◽

1998 ◽

Vol 120 (1) ◽

pp. 26-32 ◽

Cited By ~ 9

Author(s):

T. A. Cruse ◽

R. C. Dommarco ◽

P. C. Basti´as

Keyword(s):

Shear Strength ◽

Thermal Barrier Coating ◽

Bond Coat ◽

Low Cycle Fatigue ◽

High Stress ◽

Test Method ◽

Thermal Barrier ◽

Cycle Fatigue ◽

Air Plasma ◽

Barrier Coating

The static and low cycle fatigue strength of an air plasma sprayed (APS) partially stabilized zirconia thermal barrier coating (TBC) is experimentally evaluated. The shear testing utilized the Iosipescu shear test arrangement. Testing was performed parallel to the TBC-substrate interface. The TBC testing required an innovative use of steel extensions with the TBC bonded between the steel extensions to form the standard losipescu specimen shape. The test method appears to have been successful. Fracture of the TBC was initiated in shear, although unconstrained specimen fractures propagated at the TBC-bond coat interface. The use of side grooves on the TBC was successful in keeping the failure in the gage section and did not appear to affect the shear strength values that were measured. Low cycle fatigue failures were obtained at high stress levels approaching the ultimate strength of the TBC. The static and fatigue strengths do not appear to be markedly different from tensile properties for comparable TBC material.

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