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Laser Thermal Gradient Testing and Fracture Mechanics Study of a Thermal Barrier Coating

  • Yingsang Wu
  • Pei-feng HsuEmail author
  • Yao Wang
  • Mary Helen McCay
  • D. Edward Croy
  • David Moreno
  • Lei He
  • Chao Wang
  • Hongqi Zhang
Peer Reviewed
  • 40 Downloads

Abstract

It is critical for thermal barrier coating (TBC) development that a testing method be used to understand the potential and limitation of a coating’s durability and integrity under gas turbine engine operating conditions. To this end, a TBC-coated button is tested using a laser high-heat flux facility. The ceramic coating is ZrO2-8 wt.% Y2O3 applied via the air plasma spraying process on top of a NiCoCrAlY bond coating and an Inconel alloy 617 substrate button of 25.4 mm diameter. The coated button is subject to precisely controlled laser heating on the top side (1150 °C) and a temperature gradient of 63.9 °C/mm through the button overall thickness. The coated button lasts 160.9 h or 570 cycles of laser heating. The void fraction change before and after the test, the thermal conductivity change during the laser test and the failure assessment are presented. After the test, significant horizontal cracks exist in the top coating close to the thermally grown oxide (TGO) layer and near the button center. Based on the cracks and the TGO layer geometry, the stress intensity factor and strain energy release rate are computed. The combined experimental and computational approach can lead to a TBC lifetime model.

Keywords

crack analysis energy release rate finite element analysis laser thermal gradient test thermal barrier coating thermally grown oxides yttria-stabilized zirconia 

List of Symbols

APS

Air plasma spraying

BC

Bond coating

Cp

Specific heat

E

Young’s modulus

FWHM

Full-width at half-maximum

G

Strain energy release rate

K

Stress intensity factor

kn

Normalized thermal conductivity

k

Thermal conductivity

SEM

Scanning electron microscope

SUB

Substrate superalloy

TBC

Thermal barrier coatings

TC

Top coating

TGO

Thermally grown oxides

T

Temperature

TH

Hot side or top side of button temperature

TL

Cold side or bottom side of button substrate temperature

YSZ

Yttria stabilized zirconia

α

Coefficient of thermal expansion

ρ

Density

v

Poisson’s ratio

Notes

Acknowledgments

The authors wish to acknowledge the support of laser high-heat flux testing by Shanghai Electric Gas Turbine Co. Ltd. The support of the numerical study is provided by Florida Institute of Technology.

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Copyright information

© ASM International 2019

Authors and Affiliations

  • Yingsang Wu
    • 1
  • Pei-feng Hsu
    • 1
    Email author
  • Yao Wang
    • 1
  • Mary Helen McCay
    • 1
    • 2
  • D. Edward Croy
    • 2
  • David Moreno
    • 2
  • Lei He
    • 3
  • Chao Wang
    • 3
  • Hongqi Zhang
    • 3
  1. 1.Mechanical Engineering ProgramFlorida Institute of TechnologyMelbourneUSA
  2. 2.National Center for Hydrogen ResearchFlorida Institute of TechnologyMelbourneUSA
  3. 3.Gas Turbine InstituteShanghai Electric Gas Turbine Co. Ltd.ShanghaiChina

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