Abstract
Thermal barrier coatings (TBCs) are widely used to protect gas turbine blades but internal stress near the interface in TBCs is one of the main causes of thermal barrier failure under thermal cycling. A non-destructive inspection technique based on Eu3+ photoluminescence piezospectroscopy has been successfully used to analyze the residual stress in TBCs, but systematic and quantitative evaluation of data processing is still needed, especially with respect to the identification of peak positions. In this work, processing methods for Eu3+ photoluminescence spectroscopy data were studied to characterize TBC internal stress. Both physical and numerical experiments were carried out where Eu3+ luminescence spectra were obtained from a sample of europium-doped yttria-stabilized zirconia (YSZ:Eu3+) under step-by-step uniaxial loading, and the simulated spectra were numerically deduced from the measured spectra. The peak shifts were then obtained by processing the spectral data in different ways (Gaussian, Lorentzian, pseudo-Voigt fitting, and the barycenter method), and comparing the results. We found that the Gaussian function, rather than the commonly used Lorentzian function, is the most appropriate method for the application of Eu3+ photoluminescence piezospectroscopy in TBCs because it provides sufficient sensitivity, stability and confidence for quantitative stress analysis.
Highlights
Thermal barrier coatings (TBCs) are key to the development of advanced aircraft engines and energy generators because of their excellent thermal insulation and high durability, which enable them to protect gas turbine blades [1,2,3,4,5,6]
Theoretical modeling, numerical simulation, and experimental measurement are all indispensable for analyzing the state, magnitude, distribution, and evolution of the internal stress near the top coat (TC)/bonding coat (BC) interface, both for scientific research and engineering failure analysis of TBCs
The existing Cr3+ photoluminescence piezospectroscopy has been widely used for stress analysis of thermally grown oxides (TGO) in the TC/BC interface [11]
Summary
Thermal barrier coatings (TBCs) are key to the development of advanced aircraft engines and energy generators because of their excellent thermal insulation and high durability, which enable them to protect gas turbine blades [1,2,3,4,5,6]. Based on the simplified photoluminescence piezospectroscopic theory, Jiang et al [27] determined the piezospectroscopic coefficient for sprayed YSZ:Eu3+ material using a uniaxial loading system and a Raman spectrometer They measured the residual stress fields near the interface of TBCs under different thermal cycles in situ. To increase the service life of turbine blades in extremely hot and humid environments, physical-chemical-mechanical models to describe quantitatively the residual stress near the interface and non-destructive methods to evaluate the structural safety of the TBCs are needed [32] Both these goals require accurate (precision of around 10 MPa) in situ stress characterization [33]. Lu et al [45] compared the fitting results using different functions and found that the Lorentzian method was the most applicable and contributed to improving the stress measurement precision in the TGO layer based on Cr3+ photoluminescence piezospectroscopy. Tphieezpoisepzeocstproescctroopsiccocpoicefcfoiceifefinctisenwtserwe etrheetnheonbtoabintaeidnebdy bliynleianreafirtsfitosf othf ethceocrroerlraetliaotnionbebtwetweeenenthtehepepaekakshshifitftaanndduunniaiaxxiaiallssttrreessss..TThheeddiiffffeerreenntt ffiittttiinngg ffuunnccttiioonnss wweerree vveerriififieedd aanndd ccoommppaarreedd ttooddeetteerrmmiinnee tthheemmoossttrreelliiaabblleeaannddsseennssiittiivveewwaayyttoofiftitEEuu33++ pphhoottoolluummiinneesscceennccee ssppeeccttrroossccooppyyddaattaattooeevvaalluuaatteessttrreessssiinnTTBBCCss
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