基于太赫兹技术的热障涂层平行裂纹监测研究

目的监测热障涂层内部的平行裂纹。方法针对采用大气等离子喷涂方法制备的热障涂层,在内部预制不同规格的两种平行裂纹,利用反射式太赫兹时域光谱系统进行测试,获取时域谱图,联合Hanning窗函数-小波降噪滤波方法进行反卷积处理,提取不同反射峰间的时间间隔,建立数学模型进行裂纹规格参数计算。结果太赫兹时域光谱可以有效测量服役前未出现平行裂纹的热障涂层的陶瓷顶层厚度D。针对不同类型和规格的平行裂纹,通过提取时域光谱反射峰1和反射峰2的时间间隔Δt1,用于计算裂纹上端距涂层表面预制值d1和判断裂纹的位置类型。当d1

Parallel Crack Monitoring of Thermal Barrier Coatings Based on Terahertz Technology

The work aims to monitor the parallel cracks in thermal barrier coatings. For the thermal barrier coating prepared by atmospheric plasma spraying method, two kinds of cracks with different sizes were prefabricated. The time domain spectrum was obtained by the reflective Terahertz time-domain spectroscopy system, and the Hanning window function-wavelet noise reduction filtering method was used to carry out reverse-convolution to extract the featured time interval between different reflection peaks and establish mathematical models for crack dimension parameters estimation. The terahertz time-domain spectroscopy could effectively measure the D thickness of ceramic coatings without parallel cracks. For the parallel cracks with different sizes, the pre-made distance d1 between the upper surface of the crack and the top surface of ceramic coatings could be estimated by extracting the time interval Δt1 between the 1st reflection peak and the 2nd reflection peak, and it could be used to determine the location type of the crack. When d1 was smaller than D, the crack was an internal parallel crack, and when d1 was approximately equal to D, the crack was an interface parallel crack. For the larger crack with width of 130 μm, the error caused by the time interval Δt2 between the 2nd reflection peak and the 3rd reflection peak in the calculation of D was still within a reasonable range, which was about 16.47%. For the smaller crack with width of 80 μm, the error was 41.10%. The characteristic time interval Δta of the secondary reflection inside the crack which was effectively extracted by Hanning window function-wavelet noise reduction filtering method was used for the crack width estimation, and the error of the cracks with larger and smaller width was significantly reduced, respectively 4.61% and 10.01%. The experimental results showed that reverse-convolution could effectively reduce the estimation error ΔD and provide a possibility for detecting crack of narrower width. Thermal barrier coatings evaluation technology based on Terahertz time-domain spectroscopy system provides a non-contact, low-emission, on-line and non-destructive parallel cracks monitoring method, which can effectively identify and monitor the thermal crack coating interface and internal parallel cracks.