Repressing high‐temperature radiative heat transfer in thermal barrier coatings

2022 ◽  
Author(s):  
Hafiz Sartaj Aziz ◽  
Muzhang Huang ◽  
Zongyuan Li ◽  
Chunlei Wan ◽  
Wei Pan
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Thermal Barrier Coatings ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Thermal Barrier ◽  
Barrier Coatings

Near Infrared Radiative Properties of Thermal Barrier Coatings

2021 ◽  
Author(s):  
Yao Wang ◽  
Pei-feng Hsu ◽  
Yingsang Wu
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Thermal Barrier Coatings ◽  
Near Infrared ◽  
Radiative Heat ◽  
Radiative Properties ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Plasma Sprayed

Abstract Thermal barrier coatings are widely used in gas turbines to protect the gas turbine metal components against very high combustion product temperature. To improve energy efficiency, higher combustion temperatures are needed. A limiting factor at present is the stability under extreme and prolonged heating of thermal barrier coatings. The coatings are typically made by the air plasma sprayed process in which fine particles of yttria-stabilized zirconia (YSZ) are melted or partially melted and ejected from plasma jet at high speed onto the bond coated substrate metal. With increasing combustion temperature and pressure in the modern gas turbine engines radiative heat transfer is becoming an important portion of the overall heat transfer in the thermal barrier coating. This study has demonstrated that the commonly used Kubelka-Munk method in the radiative property reduction from the measured transmittance and reflectance spectra of YSZ coatings will incur inaccurate result when the coating optical thickness is not sufficiently large. An alternative method — the discrete ordinates method with the asymmetric spherical ring angular quadrature — is used instead. The absorption and scattering coefficients of air plasma sprayed YSZ films are determined over the wavelength range from 1 to 2.6 μm at room temperature. Over this near infrared wavelength range, the scattering coefficient decreases with the increasing wavelength and the absorption coefficient is very small overall. The pore size distributions before and after the 50-hr temperature gradient, thermal cycling are compared. The sintering effect as well as the crack growth will impact the coating radiative properties. These results point to a clear need for better understanding of the radiative heat transfer process, which includes the microstructure-property relationship, progressive changes of the radiative properties with the operation condition and time.

Microstructure and Heat Transfer Phenomena in Ceramic Thermal Barrier Coatings

2001 ◽  
Vol 84 (4) ◽  
pp. 827-835 ◽  
Author(s):  
Paolo Scardi ◽  
Matteo Leoni ◽  
Federico Cernuschi ◽  
Angelamaria Figari
Keyword(s):  
Heat Transfer ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Barrier Coatings

High Temperature Radiation Heat Transfer Performance of Thermal Barrier Coatings With Multiple Layered Structures

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Xiao Huang
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Thermal Barrier Coatings ◽  
Wavelength Range ◽  
Coating Thickness ◽  
Single Layer ◽  
Layered Structures ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Layered Coating

Meeting the demands for ever increasing operating temperatures in gas turbines requires concurrent development in cooling technologies, new generations of superalloys, and thermal barrier coatings (TBCs) with increased insulation capability. In the case of the latter, considerable research continues to focus on new coating material compositions, the alloying/doping of existing yttria stabilized zirconia ceramics, and the development of improved coating microstructures. The advent of the electron beam physical vapor deposition coating process has made it possible to consider the creation of multiple layered coating structures to meet specific performance requirements. In this paper, the advantages of layered structures are first reviewed in terms of their functions in impeding thermal conduction (via phonons) and thermal radiation (via photons). Subsequently, the design and performance of new multiple layered coating structures based on multiple layered stacks will be detailed. Designed with the primary objective to reduce thermal radiation transport through TBC systems, the multiple layered structures consist of several highly reflective multiple layered stacks, with each stack used to reflect a targeted radiation wavelength range. Two ceramic materials with alternating high and low refractive indices are used in the stacks to provide multiple-beam interference. A broadband reflection of the required wavelength range is obtained using a sufficient number of stacks. In order to achieve an 80% reflectance to thermal radiation in the wavelength range 0.3–5.3μm, 12 stacks, each containing 12 layers, are needed, resulting in a total thickness of 44.9μm. Using a one dimensional heat transfer model, the steady state heat transfer through the multiple layered TBC system is computed. Various coating configurations combining multiple layered stacks along with a single layer are evaluated in terms of the temperature profile in the TBC system. When compared with a base line single layered coating structure of the same thickness, it is estimated that the temperature on the metal surface can be reduced by as much as 90°C due to the use of multiple layered coating configurations. This reduction in metal surface temperature, however, diminishes with increasing the scattering coefficient of the coating and the total coating thickness. It is also apparent that using a multiple layered structure throughout the coating thickness may not offer the best thermal insulation; rather, placing multiple layered stacks on top of a single layer can provide a more efficient approach to reducing the heat transport of the TBC system.

scholarly journals Advancing Radiative Heat Transfer Modeling in High-Temperature Liquid Salts

2020 ◽  
Vol 194 (8-9) ◽  
pp. 782-792 ◽  
Author(s):  
Carolyn Coyle ◽  
Emilio Baglietto ◽  
Charles Forsberg
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Heat Transfer Modeling ◽  
Temperature Liquid ◽  
Liquid Salts

Strain Tolerance and Microstructure of Thermal Barrier Coatings Produced by Electron Beam Physical Vapor Deposition Process

2006 ◽  
Vol 522-523 ◽  
pp. 267-276 ◽  
Author(s):  
Kunihiko Wada ◽  
Yutaka Ishiwata ◽  
Norio Yamaguchi ◽  
Hideaki Matsubara
Keyword(s):  
Electron Beam ◽  
High Temperature ◽  
Thermal Barrier Coatings ◽  
Vapor Deposition ◽  
Physical Vapor Deposition ◽  
Aging Treatment ◽  
Nanoindentation Test ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Strain Tolerance

Several kinds of thermal barrier coatings (TBCs) deposited by electron beam physical vapor deposition (EB-PVD) were produced as a function of electron beam power in order to evaluate their strain tolerance. The deposition temperatures were changed from 1210 K to 1303 K depending on EB power. In order to evaluate strain tolerances of the EB-PVD/TBCs, a uniaxial compressive spallation test was newly proposed in this study. In addition, the microstructures of the layers were observed with SEM and Young’s moduli were measured by a nanoindentation test. The strain tolerance in as-deposited samples decreased with an increase in deposition temperature. In the sample deposited at 1210 and 1268 K, high-temperature aging treatment at 1273 K for 10 h remarkably promoted the reduction of the strain tolerance. The growth of thermally grown oxide (TGO) layer generated at the interface between topcoat and bondcoat layers was the principal reason for this strain tolerance reduction. We observed TGO-layer growth even in the as-deposited sample. Although the thickness of the initial TGO layer in the sample deposited at high temperature was thicker, the growth rate during aging treatment was smaller than those of the other specimens. This result suggests that we can improve the oxidation resistance of TBC systems by controlling the processing parameters in the EB-PVD process.

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