Microstructural Features Resulting From Isothermal and Thermocyclic Exposure of a Thermal Barrier Coating

Thermal barrier coating (TBC) systems are receiving a great deal of attention as a result of their ability to enable higher operating temperatures without sacrificing component durability in gas turbine systems. Nonetheless, there are a number of unknowns associated with the failure of TBC systems. In particular, the initiation and propagation of damage has not been observed. In this paper, the microstructural changes in and along the thermally growth oxide layer of a TBC are presented. Specimens were studied primarily after isothermal exposure for 48, 96, 200, and 300 hours at 1100°C and also after thermocyclic exposure. Failure features are discussed and the growth of oxide is quantified. The oxide growth is placed within the context of a parabolic growth model. [S0094-4289(00)01503-6]

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Progress in Novel Electrodeposited Bond Coats for Thermal Barrier Coating Systems

Materials ◽

10.3390/ma14154214 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4214

Author(s):

Kranthi Kumar Maniam ◽

Shiladitya Paul

Keyword(s):

Gas Turbine ◽

Thermal Barrier Coating ◽

Gas Turbines ◽

High Performance ◽

Turbine Engines ◽

Thermal Barrier ◽

Gas Turbine Engines ◽

Potential Cost ◽

Bond Coats ◽

Barrier Coating

The increased demand for high performance gas turbine engines has resulted in a continuous search for new base materials and coatings. With the significant developments in nickel-based superalloys, the quest for developments related to thermal barrier coating (TBC) systems is increasing rapidly and is considered a key area of research. Of key importance are the processing routes that can provide the required coating properties when applied on engine components with complex shapes, such as turbine vanes, blades, etc. Despite significant research and development in the coating systems, the scope of electrodeposition as a potential alternative to the conventional methods of producing bond coats has only been realised to a limited extent. Additionally, their effectiveness in prolonging the alloys’ lifetime is not well understood. This review summarises the work on electrodeposition as a coating development method for application in high temperature alloys for gas turbine engines and discusses the progress in the coatings that combine electrodeposition and other processes to achieve desired bond coats. The overall aim of this review is to emphasise the role of electrodeposition as a potential cost-effective alternative to produce bond coats. Besides, the developments in the electrodeposition of aluminium from ionic liquids for potential applications in gas turbines and the nuclear sector, as well as cost considerations and future challenges, are reviewed with the crucial raw materials’ current and future savings scenarios in mind.

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Evaluation of Impact Properties of Thermal Barrier Coating on Gas Turbine Components.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A ◽

10.1299/kikaia.66.1841 ◽

2000 ◽

Vol 66 (650) ◽

pp. 1841-1846

Author(s):

Hiroshige ITOH ◽

Kazuhiro SAITOH ◽

Takahiro KUBO ◽

Masashi TAKAHASHI ◽

Hideo KASHIWAYA

Keyword(s):

Gas Turbine ◽

Thermal Barrier Coating ◽

Thermal Barrier ◽

Impact Properties ◽

Barrier Coating

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Oxygen Transport Through the Zirconia Top Coat in Thermal Barrier Coating Systems

Thermal Spray 1998: Proceedings from the International Thermal Spray Conference ◽

10.31399/asm.cp.itsc1998p1589 ◽

1998 ◽

Author(s):

A.C. Fox ◽

T.W. Clyne

Keyword(s):

Thermal Barrier Coating ◽

Bond Coat ◽

Ionic Conduction ◽

Gas Permeability ◽

Gas Permeation ◽

Thermal Barrier ◽

Barrier Coating ◽

Oxygen Gas ◽

Plasma Sprayed ◽

Tbc Systems

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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On the Change in Stress State Associated with Bond Coat Oxidation during Heat Treatment of a Thermal Barrier Coating System

Thermal Spray 1997: Proceedings from the United Thermal Spray Conference ◽

10.31399/asm.cp.itsc1997p0267 ◽

1997 ◽

Author(s):

Y.C. Tsui ◽

T.W. Clyne ◽

R.C. Reed

Keyword(s):

Heat Treatment ◽

Stress State ◽

Oxide Layer ◽

Thermal Barrier Coating ◽

Bond Coat ◽

Driving Forces ◽

Lateral Strain ◽

Thermal Barrier ◽

Residual Stress State ◽

Barrier Coating

Abstract Thermal barrier coating systems have been heat treated in order to study the oxidation kinetics of the bond coat. All the surfaces of Ni superalloy substrates were sprayed with ~100 μm of a NiCrAlY bond coat, with or without ~250 μm of a ZrO2 top coat. Thermogravimetric analysis (TGA) was used to monitor continuously the mass change as a result of oxidation of the bond coat during heating at 1000°C for 100 hours in flowing air. In addition, some specimens were heated to 1000°C in static air, cooled to room temperature, weighed and re-heated cyclically. The total exposure time was 1000 hours. Rates of weight gain were found to be higher for the cycled specimens, despite the absence of air flow. This is attributed to damage to the oxide film, which was predominantly α-Al2O3, as a consequence of differential thermal contraction stresses. The changing residual stress state during heat treatment was predicted using a previously-developed numerical model. A thin (1 mm) substrate with ~100 μm bond coat and ~250 μm ZrO2 top coat was used in these simulations, which incorporated creep of the bond coat and the lateral strain associated with oxidation. It is concluded from these computations that, while high stresses develop in the oxide layer, the associated driving forces for interfacial debonding remain relatively low, as do specimen curvature changes. It seems likely that coating spallation after extensive oxide layer formation arises because the interface is strongly embrittled as the layer thickens.

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Field Evaluation of 2CaO-SiO2-CaO-ZrO2 Thermal Barrier Coating on Gas Turbine Vanes

Thermal Spray 1997: Proceedings from the United Thermal Spray Conference ◽

10.31399/asm.cp.itsc1997p0299 ◽

1997 ◽

Author(s):

N. Mifune ◽

Y. Harada ◽

H. Taira ◽

S. Mishima

Keyword(s):

Gas Turbine ◽

Thermal Barrier Coating ◽

Thermal Barrier Coatings ◽

Field Evaluation ◽

Thermal Barrier ◽

Barrier Coatings ◽

Thermal Change ◽

Barrier Coating ◽

Turbine Vanes ◽

Higher Temperature

Abstract Higher-temperature operation in a gas turbine has urged development of heat-resistant coatings and thermal barrier coatings. We have developed a 2CaO-SiO2-CaO-ZrO2 based thermal barrier coating. This coating should effectively prevent separation of the coating by relieving the shear stress generated due to thermal change of environment between layers with dissimilar properties. The coating was applied to stationary vanes of an actual gas turbine in a 25,000-hour test. This paper describes the results of the field test.

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