Development of Life Predictive Method For Thermal Barrier Coating Systems

本研究的目的是建立热障涂层系统的评估方法和寿命预测方法，特别是针对先进的燃气轮机叶片前沿，总结了以下个别任务的研究结果。任务(1)热障涂层试件的制备：采用空气等离子喷涂和电子束-物理气相沉积技术制备了顶层为氧化锆、粘结涂层为NiCrAlY的热障涂层试件。试件的几何形状是模拟前沿曲率的圆柱管，衬底是镍基超合金。任务(2)界面性能评估(2-1)采用激光加热方法对带有热障涂层的圆柱形试件进行了热冲击/疲劳试验。采用空气强制冷却循环来模拟TRIP过程中的热瞬变过程。采用声发射方法对激光加热实验中的断裂过程进行了研究。带…的IT此外，声发射监测还表明，顶层涂层的屈曲导致了TBC系统的最终层裂。此外，根据TBC内部的温度梯度和失效循环次数来评估高温氧化对层裂的影响。(2-2)参照圆柱形试件的几何形状，使用有限元方法进行热应力分析。在热应力分析中考虑了界面裂纹。任务(3)利用激光加热热冲击/疲劳试验获得的界面裂纹扩展实验数据，通过有限元确定的界面裂纹应力强度因子，建立了基于断裂力学的疲劳裂纹扩展速率关系式，并用该关系式再现了激光加热实验中的断裂过程。结果表明，预测的临界界面裂纹长度与激光加热实验结果接近，表明基于断裂力学的寿命预测方法是有效的。较少

The objective of this research is to develop evaluation methods of charcterizing thermal barrier coating (TBC) systems and predictive methodology of their life with special reference to a leading edge of advanced gas turbine blades, The research results are summarized for the following individual task.Task (1) Preparation of TBC specimens : TBC specimens with a top coat of ZrO and a bond coat of NiCrAlY were prepared by air plasma splay and electron beam-physical vapor deposition techniques. The specimen geometry was a cylindrical tube for simulating the curvature of leading edges and the substrate was a Ni-based superal loy.Task (2) Evaluation of interface properties(2-1) Thermal shock/fatigue tests were conducted on the cylindrical specimens with the TBCs using a laser heating method. A air-forced cooling cycle was employed to simulate the thermal transient history during trips. An acoustic emission method was used to examine the fracture process in the laser heating experiment. It w … More as shown from the AE monitoring that the buckling of the top coating layer induced the final spallation of the TBC system. Furthermore, the effect of high-temperature oxidation on the spallation was evaluated in terms of the thermal gradient within the TBC and the number of cycles to failure.(2-2) Thermal stress analyses using a FEM method were performed with reference to the cylindrical specimen geometry. The interface crack was accounted for in the thermal stress analyses. The stress intensity factor was determined as a function of interfacial crack length which formed a foundation for the analysis of the spallation behavior of the TBCs.Task (3) The experimental data of interface crack growth obtained from the laser heating thermal shock/fatigue tests were used to produce the fracture mechanics based relationship of fatigue crack growth rate through the interfacial crack stress intensity factor as determined by the FEM, The relationship was then used to reproduce the fracture process in the laser heating experiment. It was demonstrated that the predicted critical interfacial crack length was close to that observed in the laser heating experiment, indicating the validity of the fracture mechanics based life predictive method. Less