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Research Papers

A Comparative Experimental Study on Radiative Properties of EB-PVD and Air Plasma Sprayed Thermal Barrier Coatings

[+] Author and Article Information
G. Yang

Institute of Engineering Thermophysics,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China

C. Y. Zhao

Institute of Engineering Thermophysics,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: changying.zhao@sjtu.edu.cn

1Corresponding author.

Manuscript received May 24, 2014; final manuscript received February 9, 2015; published online May 14, 2015. Assoc. Editor: L. Q. Wang.

J. Heat Transfer 137(9), 091024 (Sep 01, 2015) (12 pages) Paper No: HT-14-1344; doi: 10.1115/1.4030243 History: Received May 24, 2014; Revised February 09, 2015; Online May 14, 2015

In this paper, the radiative properties of electron beam physical vapor deposition (EB-PVD) and air plasma sprayed (APS) partially yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) have been comparatively studied for the first time by measuring the spectral diffuse reflectance and transmittance in a broad spectral band ranging from 250 nm to 15 μm. The radiation transfer mechanisms inside the coatings are explored based on the experimental data and theoretical model. The results indicate that the distinctive micronanostructures of APS and EB-PVD coatings have an important effect on the radiative heat transfer. In particular, the larger grain boundary and the total porosity strongly affect the volume scattering properties of the coatings, and the scattering coefficient is closely related to the arrangement of grain boundary as well as the pore architecture (i.e., its size, morphology, and its distribution). Compared to the laminar microstructure of APS TBCs, the columnar microstructure of EB-PVD freestanding coatings exhibits a higher transmittance, a lower reflectance, and a larger absorption in the spectral region from 400 nm to 10 μm, which leads to an increase of the total heat flux. By modifying the microstructure of TBCs properly, the radiative heat flux can be reduced and thereby providing a better thermal protection for the metallic substrate.

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Figures

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Fig. 1

Measurement principle of hemispherical transmittance/reflectance

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Fig. 2

SEM micrographs of 8YSZ EB-PVD freestanding coatings with thickness of 200 μm; (a) cross section of coating and (b) top surface of coating

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Fig. 3

Microstructure feature of cross section of 8YSZ EB-PVD coatings; (a) bottom features of 200 μm freestanding coatings and (b) top features of 200 μm freestanding coatings

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Fig. 4

Cross-sectional SEM micrographs revealing feathery striations; (a) the primary columns with feathery structure and (b) feathery striations at a higher resolution

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Fig. 5

SEM micrographs of APS coating with the porosity of 15%; (a) surface section (A5) and (b) cross section (A5)

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Fig. 6

Spectral normal-hemispherical reflectance of 8YSZ APS and EB-PVD freestanding coatings

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Fig. 7

Spectral normal-hemispherical transmittance of 8YSZ APS and EB-PVD freestanding coatings

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Fig. 8

Emittance/absorptance spectra of 8YSZ APS and EB-PVD freestanding coatings

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Fig. 9

Effects of grain boundary and porosity on the normal-hemispherical reflectance of 8YSZ APS and EB-PVD freestanding coatings

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Fig. 10

Effects of grain boundary and porosity on the normal-hemispherical transmittance of 8YSZ APS and EB-PVD freestanding coatings

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Fig. 11

Effects of grain boundary and porosity on the emittance/absorptance spectra of 8YSZ APS and EB-PVD freestanding coatings

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Fig. 12

Spectral scattering coefficients of EB-PVD coatings

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Fig. 13

Spectral absorption coefficients of EB-PVD coatings

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Fig. 14

Spectral scattering coefficients for APS and EB-PVD TBCs

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Fig. 15

Spectral absorption coefficients for APS and EB-PVD TBCs

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Fig. 16

Temperature distribution in the coating-metallic systems, parameters: Tgas = 1950 K, Tsurr = 1700 K, hgas = 2200 W/(m2.K), hair = 1000 W/(m2.K), εgas = 0.3, εsurr = 1.0, εsub = 0.6, ksub = 25.4 W/(m·K), n = 2.1, porosity = 17.1%(APS), porosity = 17.3%(EB-PVD), thickness = 200 μm (TBCs), thickness = 0.8 mm (metal)

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