Residual stress generated during the high-temperature service of thermal barrier coatings is the key factor leading to their failure. The present research paper details the development, comprehensive characterisation, and mechanistic investigation of a novel series of Y3Al5O12:xCe³⁺ (YAG:xCe, x = 0.03, 0.06, 0.08, 0.12) fluorescent stress-responsive units, which have been engineered specifically for the non-destructive, in-situ stress monitoring of thermal barrier coatings (TBCs). The primary objective is to establish and optimize the critical linkage between the atomic-scale structure, governed by dopant concentration, and the macroscopic stress-sensing performance, thus surpassing conventional fluorescence intensity optimization. The YAG:xCe composite powders were synthesised via a solid-state reaction at 1 400 °C for 6 hours under a vacuum atmosphere, with high-purity Y3Al5O12 and CeO2 as precursors. The resulting phase-pure powders, confirmed by X-ray diffraction (XRD), were subsequently deposited as ceramic layers onto substrates using atmospheric plasma spraying (APS) with meticulously controlled parameters (current: 620 A, primary gas: Ar). A suite of advanced characterization techniques was employed: X-ray diffraction (XRD) with Rietveld refinement was utilized for the precise determination of lattice parameters. Photoluminescence (PL) spectroscopy was employed for excitation/emission analysis. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) was used for microstructural and elemental mapping. Density functional theory (DFT) calculations were conducted for electronic structure analysis. The experimental data revealed a definitive and nuanced structure-property relationship. XRD Rietveld refinement quantified a systematic linear increase in the cubic lattice parameter from approximately 12.010 1 Å (x=0.03) to 12.019 2 Å (x=0.12), providing direct evidence of lattice expansion due to the larger ionic radius of Ce3+ (1.14 Å) compared to Y3+ (1.019 Å). Photoluminescence studies demonstrated that the absolute fluorescence intensity peaked at a doping concentration of x=0.06, indicative of the onset of concentration quenching at higher levels. Crucially, and diverging from simple intensity-based optimization, the stress-sensing sensitivity—defined by the magnitude of fluorescence peak shift (piezospectroscopic coefficient) per unit applied stress—reached its maximum at a different, higher concentration of x=0.08. This pivotal finding of decoupled optimal concentrations for luminescence efficiency (x=0.06) and stress sensitivity (x=0.08) forms the central innovation of this work. It is explained by a competitive mechanism: while higher doping enhances lattice strain and crystal field tunability (beneficial for sensitivity), it also concurrently increases non-radiative energy transfer pathways (detrimental to overall brightness). The YAG:0.08Ce composition represents the optimal balance where the strain-induced enhancement of the crystal field's responsivity to external stress outweighs the detrimental effects of incipient quenching. DFT calculations corroborate this by showing a downshift in the Ce³+ energy levels with increased doping, which directly lowers the 4f-5d transition energy, manifesting as the observed red-shift in emission spectra. In conclusion, the present study successfully constructs a series of YAG:xCe fluorescent stress-responsive units and demonstrates that their luminescence efficiency and stress-responsive characteristics can be effectively tuned by the doping concentration. The structure-property relationship among doping concentration, lattice distortion, and the piezospectroscopic effect is elucidated. The present work provides a substantial material system and theoretical foundation for achieving highly sensitive, non-destructive, and in-situ monitoring of the internal stress state in TBCs, thus offering positive support for the health monitoring and lifetime prediction of next-generation aero-engine thermal barrier coatings.
Key words
thermal barrier coatings /
fluorescence /
stress /
YAG:Ce
{{custom_sec.title}}
{{custom_sec.title}}
{{custom_sec.content}}
References
[1] PADTURE N P, GELL M, JORDAN E H.Thermal Barrier Coatings for Gas-Turbine Engine Applications[J]. Science, 2002, 296(5566): 280-284.
[2] CLARKE D R, OECHSNER M, PADTURE N P.Thermal-Barrier Coatings for More Efficient Gas-Turbine Engines[J]. MRS Bulletin, 2012, 37(10): 891-898.
[3] VAßEN R, JARLIGO M O, STEINKE T, et al. Overview on Advanced Thermal Barrier Coatings[J]. Surface and Coatings Technology, 2010, 205(4): 938-942.
[4] 李荣斌, 邢悦, 张志玺, 等. 等离子喷涂YSZ热障涂层的工艺研究[J]. 表面技术, 2024, 53(7): 217-229.
LI R B, XING Y, ZHANG Z X, et al.Plasma Spraying Process of YSZ Thermal Barrier Coatings[J]. Surface Technology. 2024, 53(7): 217-229.
[5] 华佳捷, 张丽鹏, 刘紫微, 等. 热障涂层失效机理研究进展[J]. 无机材料学报, 2012, 27(7): 680-686.
HUA J J, ZHANG L P, LIU Z W, et al.Progress of Research on the Failure Mechanism of Thermal Barrier Coatings[J]. Journal of Inorganic Materials, 2012, 27(7): 680-686.
[6] GOTOH N, OGAWA K, SHOJI T, et al. Nondestructive Evaluation of High-Temperature Oxidation Behaviour in Thermal Barrier Coatings (High Temperature Materials)[J]. Proceedings of the Asian Pacific Conference on Fracture and Strength and International Conference on Advanced Technology in Experimental Mechanics, 2001, 1.01.203: 303-308.
[7] MANERO A, SELIMOV A, FOULIARD Q, et al.Piezospectroscopic Evaluation and Damage Identification for Thermal Barrier Coatings Subjected to Simulated Engine Environments[J]. Surface and Coatings Technology, 2017, 323: 30-38.
[8] LU N, ZHANG Y H, QIU W.Comparison and Selection of Data Processing Methods for the Application of Cr3+ Photoluminescence Piezospectroscopy to Thermal Barrier Coatings[J]. Coatings, 2021, 11(2): 181.
[9] LI C, ZHANG X, CHEN Y, et al.Understanding the Residual Stress Distribution through the Thickness of Atmosphere Plasma Sprayed (APS) Thermal Barrier Coatings (TBCS) by High Energy Synchrotron XRD; Digital Image Correlation (DIC) and Image Based Modelling[J]. Acta Materialia, 2017, 132: 1-12.
[10] 罗军, 李楠, 王曦, 等. 中子衍射在航空发动机材料残余应力分析中的应用[J]. 材料导报, 2023, 37(S2): 497-508.
LUO J, LI N, WANG X, et al.Application of Neutron Diffraction in Residual Stress Analysis of Aero-Engine Materials[J]. Materials Reports, 2023, 37(S2): 497-508.
[11] CHRISTENSEN R J, LIPKIN D M, CLARKE D R, et al.Nondestructive Evaluation of the Oxidation Stresses through Thermal Barrier Coatings Using Cr3+ Piezospectroscopy[J]. Applied Physics Letters, 1996, 69(24): 3754-3756.
[12] ZHAO Y, MA C L, HUANG F X, et al.Residual Stress Inspection by Eu3+ Photoluminescence Piezo-Spectroscopy: An Application in Thermal Barrier Coatings[J]. Journal of Applied Physics, 2013, 114(7): 073502.
[13] ZHANG S J, ZHANG Y H, WANG Z, et al.YAG: Ce3+ Piezo-Spectroscopy: A High-Sensitive Method Used for Stress Characterization of Thermal Barrier Coating[J]. International Journal of Applied Ceramic Technology, 2022, 19(5): 2623-2631.
[14] KUMAR R, JORDAN E, GELL M, et al.CMAS Behavior of Yttrium Aluminum Garnet (YAG) and Yttria-Stabilized Zirconia (YSZ) Thermal Barrier Coatings[J]. Surface and Coatings Technology, 2017, 327: 126-138.
[15] BACHMANN V, RONDA C, MEIJERINK A.Temperature Quenching of Yellow Ce3+ Luminescence in YAG: Ce[J]. Chemistry of Materials, 2009, 21(10): 2077-2084.
[16] HE X W, LIU X F, LI R F, et al.Effects of Local Structure of Ce3+ Ions on Luminescent Properties of Y3Al5O12:Ce Nanoparticles[J]. Scientific Reports, 2016, 6: 22238.
[17] VALIEV D, HAN T, VAGANOV V, et al.The Effect of Ce3+ Concentration and Heat Treatment on the Luminescence Efficiency of YAG Phosphor[J]. Journal of Physics and Chemistry of Solids, 2018, 116: 1-6.
[18] MEHBOOB G, LIU M J, XU T, et al.A Review on Failure Mechanism of Thermal Barrier Coatings and Strategies to Extend Their Lifetime[J]. Ceramics International, 2020, 46(7): 8497-8521.
[19] HA H, YANG S, PARK S.Photoluminescence Spectra Correlations with Structural Distortion in Eu3+-and Ce3+-Doped Y3Al5-2x(Mg,Ge)xO12 (x=0, 1, 2) Garnet Phosphors[J]. Materials, 2024, 17(10): 2445.
[20] LINDERÄLV C, ÅBERG D, ERHART P. Luminescence Quenching via Deep Defect States: A Recombination Pathway via Oxygen Vacancies in Ce-Doped YAG[J]. Chemistry of Materials, 2021, 33(1): 73-80.
[21] ZHANG X J, SUN X R, LIU H S, et al.The Effect of Ce Concentration on the Structural and Optical Properties of YGG: Ce Phosphor[J]. Materials Chemistry and Physics, 2022, 278: 125619.
[22] WANG Z, ZHANG Y, ZHANG S, et al.Electronic Structure and Optical Properties of Ce-Doped Y3Al5O12 Crystals: A First-Principles Study[J]. Computational Materials Science, 2023, 217: 111876.
[23] ZHAO X, XIAO P.Residual Stresses in Thermal Barrier Coatings Measured by Photoluminescence Piezospectroscopy and Indentation Technique[J]. Surface and Coatings Technology, 2006, 201(3/4): 1124-1131.
[24] HU S H, JU M, WANG P, et al.Investigation of the Microstructure and Electronic Features for Ce3+-Doped YAG Crystal: A First-Principle Study[J]. Computational Materials Science, 2021, 200: 110762.
[25] KUNTI A K, PATRA N, HARRIS R A, et al.Structural Properties and Luminescence Dynamics of CaZrO3:Eu3+ Phosphors[J]. Inorganic Chemistry Frontiers, 2021, 8(3): 821-836.
[26] 白易博, 丁呈云, 楚倩倩, 等. La2Zr2O7/YSZ双陶瓷热障涂层的深层应力荧光检测[J]. 粉末冶金材料科学与工程, 2025, 30(5): 405-413.
BAI Y B, DING C Y, CHU Q Q, et al.Fluorescence Detection of Deep-Seated Stresses Inside La2Zr2O7/YSZ Double-Ceramic Thermal Barrier Coatings[J]. Materials Science and Engineering of Powder Metallurgy, 2025, 30(5): 405-413.
Funding
National Natural Science Foundation of China (52462010); Gansu Provincial Science and Technology Program Basic Research Plan Projects (25JRRA055, 25JRRA077); Lanzhou University of Technology Young Faculty Interdisciplinary Research Cultivation Project; "111" Program (D21032)
PDF(4458 KB)
