Time of flight improved thermally grown oxide thickness measurement with terahertz spectroscopy

Zhang, Zhenghao; Huang, Yi; Zhong, Shuncong; Lin, Tingling; Zhong, Yujie; Zeng, Qiuming; Nsengiyumva, Walter; Yu, Yingjie; Peng, Zhike

doi:10.1007/s11465-022-0705-3

Cited by 5 publications

(5 citation statements)

References 45 publications

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“…ECT Large internal coating pores, the remaining thickness of the top Completed the detection of the (1) TC layer with a thickness of 244 µm, with an error of 1.4%; (2) thickness and conductivity of bond coating to detect delamination. (c) Thermal barrier coating structure [4].…”

Section: Thicknessmentioning

confidence: 99%

“…Thermal barrier coatings (TBCs) on the aeroengine turbine blades are an important factor in improving the operating efficiency of the engine [2,3]. As shown in the following picture, Figure 1a is a turbine engine, Figure 1b is the blade of a turbine engine, and the typical structure of the thermal barrier coatings is shown in Figure 1c [4], which consists of super alloy, bond coat (BC), and ceramic layer (Topcoat, TC). The propagation of microcracks on the TC layer and the thickening of thermally grown oxide (TGO) caused by oxidation at high temperatures are the main factors causing the failure of TBCs [5].…”

Section: Introductionmentioning

confidence: 99%

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Combined Terahertz Pulsed Imaging and Optical Coherence Tomography Detection Method for Multiple Defects in Thermal Barrier Coatings

Luo,

Zhong,

Huang

et al. 2024

Coatings

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While thermal barrier coatings (TBCs) are being sprayed onto aero-engine turbine blades, or while the engine blade is working, high temperatures and strong impact forces will damage TBCs under thermal cycles, resulting in the coating peeling off from the blades. The current method of using ECT, IRT, or another method alone cannot achieve the real-time detection of coating defects with both high precision and high penetration power. Two detection methods, namely, terahertz pulsed imaging (TPI) and optical coherence tomography (OCT), were combined to evaluate typical defects observed in TBCs (including internal debonding cracks, surface high-temperature cracks, and surface etched cracks). The results showed that the OCT system successfully obtained the micron-level axial resolution, but the detection depth of the OCT system was limited. The TPI system achieved a higher penetration depth than OCT—hence, it can be used for the nondestructive detection and evaluation of the internal debonding defects in the sample—but its resolution needs to be improved. Following this conclusion, a method is proposed using TPI and OCT concurrently for the nondestructive testing and quantitative evaluation of TBCs on etched cracks, thus achieving progress both in terms of depth and resolution. In our experiment, defects with a depth of 519 μm and a width of 100 μm were measured. The proposed method is suitable for situations where multiple defects in TBC samples of blades need to be detected simultaneously during the working process. When there are defects deep inside the sample, more small cracks on the surface can be evaluated to achieve a combination of depth and accuracy.

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Section: Thicknessmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Combined Terahertz Pulsed Imaging and Optical Coherence Tomography Detection Method for Multiple Defects in Thermal Barrier Coatings

Luo,

Zhong,

Huang

et al. 2024

Coatings

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“…After the calculation of the results in Eqs. ( 8)- (10), the values of refractive indices for both the reference GFRP composite laminate and Teflon film were obtained as presented in The average value of the calculated real part of the refractive index n of the GFRP composite sample and the PTFE film is found to be 2.157 and 1.462, respectively, at the frequency of 0.45 THz. Figure 6 indicates that the refractive indices for both materials remain almost steady (i.e., they vary very little in the considered range of frequencies) while the absorption coefficients of these two materials (i.e., the GFRP composite sample and the Teflon film) continuously increase in the same range of frequencies.…”

Section: Optical Parameters Of the Samplesmentioning

confidence: 99%

“…In the field of materials and structural systems testing, terahertz (THz) technology has recently become one of the most promising NDT techniques, thanks to the adaptive physical modeling of the transmission process of the THz waves and their high-penetration capabilities in non-conducting materials [8][9][10]. The THz part of the electromagnetic spectrum extends from 0.1 to 10 THz (i.e., corresponding to the wavelength ranging from 3 mm down to 30 μm), and lies between the microwave and infrared regions of the electromagnetic spectrum.…”

Section: Introductionmentioning

confidence: 99%

Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites

Nsengiyumva

Zhong

Luo

et al. 2023

Chin. J. Mech. Eng.

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The use of terahertz time-domain spectroscopy (THz-TDS) for the nondestructive testing and evaluation (NDT&E) of materials and structural systems has attracted significant attention over the past two decades due to its superior spatial resolution and capabilities of detecting and characterizing defects and structural damage in non-conducting materials. In this study, the THz-TDS system is used to detect, localize and evaluate hidden multi-delamination defects (i.e., a three-level multi-delamination system) in multilayered GFRP composite laminates. To obtain accurate results, a wavelet shrinkage de-noising algorithm is used to remove the noise from the measured time-of-flight (TOF) signals. The thickness and location of each delamination defect in the z-direction (i.e., through-the-thickness direction) are calculated from the de-noised TOF signals considering the interaction between the pulsed THz waves and the different interfaces in the GFRP composite laminates. A comparison between the actual and the measured thickness values of the delamination defects before and after the wavelet shrinkage denoising process indicates that the latter provides better results with less than 3.712% relative error, while the relative error of the non-de-noised signals reaches 16.388%. Also, the power and absorbance levels of the THz waves at every interface with different refractive indices in the GFRP composite laminates are evaluated based on analytical and experimental approaches. The present study provides an adequate theoretical analysis that could help NDT&E specialists to estimate the maximum thickness of GFRP composite materials and/or structures with different interfaces that can be evaluated by the THz-TDS. Also, the accuracy of the obtained results highlights the capabilities of the THz-TDS for the NDT&E of multilayered GFRP composite laminates.

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“…Chen et al [20] proposed the use of the terahertz reflection method combined with the time-domain simulation technique for the characterization of the interfacial oxide layer. Zhang et al [21] proposed an improved time of flight (TOF) method for measuring the TGO thickness in TBCs using terahertz time-domain spectroscopy. The method achieved efficient and accurate TGO thickness measurement, making it suitable for condition monitoring and life prediction of TBCs.…”

Section: Introductionmentioning

confidence: 99%

Multi-Scale Analysis of Terahertz Time-Domain Spectroscopy for Inversion of Thermal Growth Oxide Thickness in Thermal Barrier Coatings

et al. 2023

Coatings

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To address the inverse problem of thermal growth oxide (TGO) thickness in thermal barrier coatings (TBCs), a novel multi-scale analysis (MSA) method based on terahertz time-domain spectroscopy (THz-TDS) is introduced. The proposed method involves a MSA technique based on four wavelet basis functions (db4, sym3, haar, coif3). Informative feature parameters characterizing the TGO thickness were extracted by performing continuous wavelet transform (CWT) and max-pooling operations on representative wavelet coefficients. Subsequently, multi-linear regression and machine learning regression models were employed to predict and assess the wavelet feature parameters. Experimental results revealed a discernible trend in the wavelet feature parameters obtained through CWT and max-pooling in the MSA, wherein the visual representation of TGO thickness initially increases and then gradually decreases. Significant variations in these feature parameters with changes in both thickness and scale enabled the effective inversion of TGO thickness. Building upon this, multi-linear regression and machine learning regression prediction were performed using multi-scale data based on four wavelet basis functions. Partial-scale data were selected for multi-linear regression, while full-scale data were selected for machine learning regression. Both methods demonstrated high accuracy prediction performance. In particular, the haar wavelet basis function exhibited excellent predictive performance, as evidenced by regression coefficients of 0.9763 and 0.9840, further confirming the validity of MSA. Hence, this study effectively presents a feasible method for the inversion problem of TGO thickness, and the analysis confirms the promising application potential of terahertz time-domain spectroscopy’s multi-scale analysis in the field of TBCs evaluation. These findings provide valuable insights for further reference.

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Time of flight improved thermally grown oxide thickness measurement with terahertz spectroscopy

Cited by 5 publications

References 45 publications

Combined Terahertz Pulsed Imaging and Optical Coherence Tomography Detection Method for Multiple Defects in Thermal Barrier Coatings

Combined Terahertz Pulsed Imaging and Optical Coherence Tomography Detection Method for Multiple Defects in Thermal Barrier Coatings

Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites

Multi-Scale Analysis of Terahertz Time-Domain Spectroscopy for Inversion of Thermal Growth Oxide Thickness in Thermal Barrier Coatings

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