【作者】 杨玉娥；

【导师】 何存富；

【作者基本信息】 北京工业大学 ， 机械工程， 2013， 博士

【摘要】 为了提高发动机的热效率，热障涂层（Thermal Barrier Coatings，简称TBCs）已经被广泛应用到发动机的涡轮叶片等热端部件上，热障涂层是在叶片等热端部件表面涂覆的具有一定厚度和耐久性的绝热陶瓷层薄膜。由于热障涂层的制备工艺复杂，在制备过程中制备工艺参数的变化会影响热障涂层的厚度和孔隙率等结构性能，热障涂层的结构性能直接影响其热障效果；高温的工作环境会造成各层间粘结状况差的位置脱粘，并且产生的热生长氧化层（Thermal Growth Oxide，简称TGO层）会促进脱粘现象的产生。为了保证热障涂层良好的热障效果，并避免在工作过程中失效而造成不必要的损失，急需一种可以在位检测的无损检测方法。微波无损检测技术是一种新型的无损检测技术，因其具有穿透介电材料的能力强、对界面和不均匀性很敏感等特点，适合对热障涂层进行无损检测。根据热障涂层的结构特性，适合用微波反射法对其进行无损检测。本文在电磁波理论的指导下，利用微波无损检测技术对热障涂层中陶瓷顶层（Top coating，简称TC层）的厚度、孔隙率等结构特性，粘结层（Bond coating，简称BC层）表面的裂缝、TC层与BC层间的脱粘等健康状况参数，以及TC层和BC层间的TGO层进行了检测和评价。主要以理论分析和数值模拟为指导，通过优化检测参数进行了试验研究，提出了一种高频、宽带、高分辨率，适合热障涂层检测的微波无损检测方法。主要工作如下：(1)建立了微波反射系数法检测热障涂层的理论模型。通过模型的建立可知，在检测中探头的特性、工作频率以及提离距离会影响检测的灵敏度，因此在检测前需要对这几个参数进行优化设计，以期达到更好的检测效果。通过对理论模型的计算可知，利用微波信号的反射系数可以表征热障涂层中各介质层的厚度、与介电常数有关的物理特性、合金层表面的健康状况以及各层间的脱粘状况等。(2)规则波导探头的参数敏感性分析。根据微波在波导中的传输条件，确定了波导中单模传播时波导尺寸与工作频率间的对应关系，以简化微波检测过程中模态分析的过程。根据微波在不同形状波导中的传播特点，以及检测空间分辨率的要求，分析了如何根据工作频率选择合适的波导探头；并分析了波导探头法兰对检测结果的影响。(3)微波检测热障涂层时检测参数的优化研究。利用CST微波工作室(Computer Simulation Technology-Microwave Studio)仿真软件对检测过程中工作频率和提离距离等参数进行了优化设计。在接触式检测中，主要对检测的工作频率进行了优化设计，根据优化的工作频率选择合适的波导探头进行无损检测以达到较高的检测灵敏度；在非接触式检测中，主要对提离距离进行了优化设计，为扫描检测时提离距离的选择奠定了理论基础。(4)微波检测热障涂层的试验研究。根据检测参数优化的结果，利用网络分析仪E8363C对热障涂层的厚度和孔隙率进行了微波无损检测试验研究。在检测工作频率范围内，可以利用微波信号的反射系数相位差，来良好的表征热障涂层厚度的变化，并且利用卡尺测量法对微波检测结果进行了标定；在敏感工作频率处，可以用微波信号的反射系数相位差，来表征热障涂层孔隙率的变化，利用切片图像分析的方法对微波无损检测结果进行了标定。(5)热障涂层健康状况的毫米波无损检测研究。选用了多种型号的终端开口矩形波导作为探头，在毫米波段对热障涂层系统中常见的缺陷进行了无损检测研究，检测中利用信号的反射系数相位差来表征被检测参数的变化。在毫米波段可以实现对热障涂层中裂缝、脱粘和TGO层的微波无损检测；利用高频率段的探头进行检测可以明显提高检测灵敏度。更多还原

【Abstract】 Thermal barrier coatings (TBCs) have been developed in order to increase theoperating temperature in gas turbine engines and some components operating inhigh-temperature condition. TBCs are thin ceramic layers with durability whichdeposited onto the hot-section components. In the process to produce TBCs, processparameters affect coating thickness profiles and morphological features, which affectthermal conductivity of TBCs. Besides, the delamination is induced by thermalstresses under the environment of high temperature and TGO. Therefore, it isnecessary to detect TBCs in order to ensure the quality of TBCs.Although not as widely known or understood as other NDE techniques,microwave non-destructive evaluation (NDE) has proven to be very useful in certainapplications. Non-contact inspection and the ability to penetrate into dielectricmaterials are two of most import attributes of microwave NDE and make it suitablefor the non-destructive inspection of TBCs. Due to the structure features of TBCs, inthis paper microwave NDE is simply based on wave reflection from a dielectric mediainterface.The objective of this paper is to investigate feasibility of microwave NDE todetect or monitor TC thickness, TC porosity, crack on BC, delamination between TCand BC and thermally grown oxide (TGO) growth. Three main works are setting upthe theory model, optimizing detecting parameters and detecting TBCs usingmicrowave NDE. Main works are as follows:(1) The theory model to detecting TBCs using wave reflection of microwaveNDE was established. An effective reflection coefficient is determined in this waywhose phase characteristics are used in the detection and evaluation of TC thickness,TC porosity, crack on BC, delamination between TC and BC and thermally grownoxide (TGO) growth. The characteristics of this phase as a function of severalparameters such as the frequency of operation, standoff distance and probe featuresare investigated.(2) The optimization of waveguide probe was carried out. According to thetransmission condition of microwave in waveguide, the relation of frequency andprobe size was presented in order to predigest model analysis of microwave in probe.How to select the appropriate probe shape was showed according to the transmissioncharacter of microwave in probe. Besides, the influence of probe flange wasdiscussed.(3) The optimization of detect parameter was carried out in microwave NDE byusing computer simulation technology-microwave studio (CST–MS). The detectparameters include frequency and standoff distance (in non-contact detection). The best parameters would be used to detect TBCs, in order to improve sensitivity ofmicrowave NDE.(4) TC thickness measurements and TC porosity monitor in TBCs system hasbeen carried out using microwave NDE. The measurement system used in this paperconsisted of a network analyzer (Agilent E8363C,100MHz-40GHz) feeding signalsto a Ka-band rectangular waveguide (Agilent R281A). The results showed that thephase difference can be used to evaluate TC thickness and porosity. The results werevalidated using destructive detection.(5) The defects of TBCs were detected using millimeter wave NDE. Four kindsof rectangular waveguides were used to detect TBCs. Changes in the phase ofreflection coefficient were primarily studied. The results showed the crack, thedelamination and TGO in TBCs, can be detected effectively using millimeter wavenondestructive testing techniques. Besides, the sensitivity is greater in high frequencythan low frequency.更多还原