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Research Papers: Gas Turbines: Ceramics

# Sensor Thermal Barrier Coatings: Remote In Situ Condition Monitoring of EB-PVD Coatings at Elevated Temperatures

[+] Author and Article Information
Rémy J. L. Steenbakker

National High Temperature Surface Engineering Centre, Cranfield University, Bedfordshire MK43 0AL, UKr.steenbakker.2003@cranfield.ac.uk

Jörg P. Feist1

Southside Thermal Sciences (STS) Ltd., c/o Imperial Innovations, Level 12, Electrical Engineering, Imperial College London, London SW7 2AZ, UKj.feist@stscience.com

Richard G. Wellman, John R. Nicholls

National High Temperature Surface Engineering Centre, Cranfield University, Bedfordshire MK43 0AL, UK

1

Corresponding author.

J. Eng. Gas Turbines Power 131(4), 041301 (Apr 10, 2009) (9 pages) doi:10.1115/1.3077662 History: Received April 09, 2008; Revised April 09, 2008; Published April 10, 2009

## Abstract

Thermal barrier coatings (TBCs) are used to reduce the actual working temperature of the high pressure turbine blade metal surface. Knowing the temperature of the surface of the TBC and at the interface between the bondcoat and the thermally grown oxide (TGO) under realistic conditions is highly desirable. As the major life-controlling factors for TBC systems are thermally activated, therefore linked with temperature, this would provide useful data for a better understanding of these phenomena and to assess the remaining lifetime of the TBC. This knowledge could also enable the design of advanced cooling strategies in the most efficient way using minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of TBCs to be realized due to improved precision in temperature measurement and early warning of degradation. This, in turn, will increase fuel efficiency and reduce $CO2$ emissions. The concept of a thermal-sensing TBC was first introduced by Choy, Feist, and Heyes (1998, “Thermal Barrier Coating With Thermoluminescent Indicator Material Embedded Therein,” U.S. Patent U.S. 6974641 (B1)). The TBC is locally modified so it acts as a thermographic phosphor. Phosphors are an innovative way of remotely measuring temperatures and also other physical properties at different depths in the coating using photo stimulated phosphorescence (Allison and Gillies, 1997, “Remote Thermometry With Thermographic Phosphors: Instrumentation and Applications,” Rev. Sci. Instrum., 68(7), pp. 2615–2650). In this study the temperature dependence of several rare earth doped EB-PVD coatings will be compared. Details of the measurements, the influence of aging, the composition, and the fabrication of the sensing TBC will be discussed in this paper. The coatings proved to be stable and have shown excellent luminescence properties. Temperature detection at ultrahigh temperatures above $1300°C$ is presented using new types of EB-PVD TBC ceramic compositions. Multilayer sensing TBCs will be presented, which enable the detection of temperatures below and on the surface of the TBC simultaneously.

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## Figures

Figure 2

Calibration curves of YSZ:Eu2%, YSZ:Gd2%, and YSZ:Dy2% EB-PVD TBCs

Figure 3

Effect of dysprosia concentration on the luminescence intensity of YSZ:Dy EB-PVD TBCs at room temperature

Figure 4

Influence of dysprosia concentration on the luminescence lifetime of YSZ:Dy EB-PVD TBCs

Figure 5

Emission spectrum of YSZ:Dy at room temperature

Figure 6

Lifetime decay measurements using three different emission wavelengths

Figure 7

Influence of aging on the phosphorescence lifetime of YSZ:Dy 2% EB-PVD TBCs

Figure 8

Luminescence spectra of the YAG:Dy EB-PVD coating and YAG:Dy powder

Figure 9

Calibration curves of YSZ:Dy and YAG:Dy EB-PVD coatings

Figure 10

SEM micrograph of the multilayer sensing EB-PVD TBC with the excitation and emission wavelengths

Figure 11

Calibration curves of the YAG:Tm and YSZ:Dy layers of the multilayer EB-PVD TBC

Figure 12

XRD graphs of the multilayer coating aged 3 h at 1100°C and 300 h, 750 h, and 1000 h at 1200°C

Figure 1

Dieke diagram; energy levels of the 4f configuration of rare earth trivalent ions (51)

## Errata

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