热震过程中热障涂层隔热层内部裂纹扩展动态行为研究

To investigate the high temperature failure mechanism of the thermal barrier coatings (TBCs) in depth is of great significance for the life assessment and prediction of the TBCs. It is beneficial to realize the tracking of the failure of the coating in time and further understand the process of the high temperature failure of the coating in depth through the study of the dynamic behavior of crack propagation. Three kinds of TBCs (double ceramic layer La2Zr2O7/8YSZ, nanostructured 8YSZ TBCs and conventional 8YSZ TBCs) will be prepared by plasma spraying in this project. The thermal shock resistance ability of the three as-sprayed coatings will be measured by heating-water quenching method. The dynamic behavior of the crack propagation during thermal shock at high temperature will be investigated by extended finite element method.The evolution law of the cracks in the heat insulation layer of the three as-sprayed TBCs during thermal shock will be observed and characterized by Scanning Electron Microscope (SEM) and Acoustic Emission Method (AEM) in orer to further validate the simulaton results. The investigation results will exhibit dynamic images of the crack propogation in the heat insulation layers of the three as-sprayed TBCs at different thermal shock temperatures, and reveal the variation characteristic of the crack propagation and the fracture parameters in the process of thermal shock, at the same time, the investigation results will also explore the failure modes and failure mechanism of the three as-sprayed coatings in depth. This study will lay the theoretical foundation for the high-temperature service life prediction of TBCs, and provide a scientific basis to further expand the application of the TBCs with excellent performance in the field of aviation, aerospace and defense.

深入研究热障涂层的高温失效机制对于热障涂层寿命的评估及预测具有十分重要的意义。通过对裂纹扩展动态行为的研究有助于实现对涂层失效过程的实时跟踪，进一步深入理解涂层高温失效的过程。本项目拟通过等离子喷涂工艺制备双陶瓷层La2Zr2O7(LZ)/8YSZ、 纳米结构8YSZ、传统结构8YSZ三种涂层。采用加热-淬水法测试三种涂层的高温抗热震性能，并结合扩展有限元方法研究三种涂层隔热层内部裂纹在热震过程中扩展的动态行为，利用扫描电镜和声发射器研究裂纹在高温热震过程中的扩展规律以验证模拟结果。研究结果将建立不同热震温度下三种涂层隔热层的内部裂纹扩展的动态图像，揭示关键裂纹在热震过程中扩展形态及断裂参数的变化规律，深入探讨三种涂层的高温热震破坏形式及失效机制。本研究将为热障涂层的高温服役寿命预测奠定理论基础，并进一步为拓展高性能热障涂层在航空、航天及国防领域的应用提供科学依据。

热障涂层作为沉积在燃气轮机叶片上的一种重要的陶瓷涂层材料, 对于提高叶片工作温度及燃气轮机的热机效率，同时使其免受高温氧化、腐蚀、磨损等具有很重要的作用。本项目以等离子喷涂YSZ (yttria stabilized zirconia, 氧化钇稳定的氧化锆) 涂层为基本研究体系，开展相应的研究工作。考虑到热障涂层材料通常工作在冷热循环交替的工况下，因此本项目着重分析在高温热震条件下涂层的失效机理。模拟计算方面，首先采用生死单元的方法对涂层的残余应力进行了模拟计算，通过残余应力的计算，进一步通过厚度优化，找到了热障涂层体系各层厚度的配比，为等离子喷涂制备实际涂层提供了重要的理论依据。此外，通过有限元模拟，计算了涂层在热震过程中的残余应力演变的规律。在涂层中引入了不同分布形态的微裂纹，计算了裂纹尖端的断裂力学参数，分析了裂纹可能的扩展趋势以及对涂层热震失效的影响规律。进一步考虑了如果在热循环过程中，打底层和陶瓷层之间形成一层热生长氧化物层。涂层中横向裂纹和纵向裂纹的分布位置对涂层中TGO及周围处的应力的影响规律。研究结果表明纵向裂纹与TGO层具有双向影响的效果。采用扩展有限元法模拟计算了涂层在热震过程中的裂纹扩展趋势。进一步我们考虑打底层中孤岛状氧化物的存在对TGO应力以及TGO处横向裂纹扩展的影响规律。采用声发射技术研究了涂层在热震下的失效行为模式及失效机理，利用自用设计的工装夹具实现了涂层在高温热冲击条件下的失效过程中的裂纹扩展的声发射信号的采集，研究结果表明：引起裂纹扩展的信号的频率段分布在102.5kHz-570kHz之间。模拟计算与声发射表征结果为燃机用热障涂层的工艺优化提供了理论支撑和实践指导。