航空发动机导叶用热障涂层高温冲蚀条件下裂纹扩展动态行为研究

Thermal barrier coatings (TBCs) which are used for the turbine blades of aero-engine (including the guide vanes and moving blades) are usually endured with coupled service conditions of high temperature impact erosion (also called foreign object damage, FOD). The failure mechanism of the TBCs is very complicated. Not only the thermal residual stress produced under the thermal-mechanic coupling conditions can cause the coating damage, but also the high temperature impact erosion can also cause failure of the coating. In our previous work, we have investigated the thermal residual stress and crack propagation of TBCs during thermal shock systematically, and the corresponding simulation algorithms and experimental characterization techniques for crack propagation were preliminarily established. The project is proposed on the basis of previous work, the plasma sprayed YSZ TBCs used for the guide vanes of the aero-engine will be studied, the nonlinear dynamic finite element calculation method will be adopted to investigate the dynamic behavior of crack propagation of the TBCs under the coupled service conditions of foreign particle erosion and alternating temperature field, the evolution mode of the residual stress and micro-cracks inside the coating under this service conditions will be analyzed. The dynamic image of crack propagation of the coating will be established. The crack propagation behavior under the coupled service conditions will be also investigated via the in situ acoustic emission technique. We will try to reveal the dynamic relationship between the characteristic parameters of acoustic emission signals of the crack propagation and the propagation modes of the cracks in the TBCs deeply. The corresponding relationship between the experimental and simulation results will be also elucidated. This study will lay a theoretical foundation for the prediction of lifetime of TBCs which are endured with high temperature impact erosion conditions, and further provide scientific basis for optimizing the preparation process of TBCs with excellent performance used for guide vanes of aero-engine.

航空发动机涡轮叶片（包括导叶和动叶）用热障涂层通常服役在高温冲蚀多因素作用的环境中，其失效机制复杂。不仅仅热力耦合条件下产生的热残余应力会引起涂层破坏，外部粒子冲蚀也会对涂层造成损伤。申请人前期对热障涂层在热震条件下的热应力及裂纹扩展进行了系统研究，初步建立了裂纹扩展相应算法及实验表征技术。本项目拟在前期工作基础上，以航空发动机导叶用等离子体喷涂YSZ热障涂层为研究对象，采用非线性动力学有限元计算手段对涂层在高温冲蚀作用下的裂纹扩展动态行为进行计算，分析在此环境中涂层内部的热残余应力、微裂纹扩展模式。建立涂层内部裂纹运动的动态图像。并采用原位声发射技术研究涂层在此耦合作用环境下的裂纹扩展行为，深入揭示裂纹扩展的声发射信号特征参数与裂纹扩展模态之间的动态联系，与模拟结果建立对应关系。本研究将为热障涂层高温冲蚀寿命预测奠定理论基础，并进一步为优化高性能航机导叶用热障涂层的制备工艺提供科学依据。

热障涂层对于提高航空发动机涡轮叶片的工作温度，提高发动机推重比及热机效率具有重要作用。然而航空发动机在运行时，带热障涂层的涡轮叶片通常受到外来的CaO-MgO-Al2O3-SiO2（CMAS）粒子和燃烧室中杂质颗粒的撞击，通常称为冲蚀，导致涂层过早剥落，是引起热障涂层失效的主要原因之一。本项目以大气等离子喷涂YSZ热障涂层为研究对象。采用有限元模拟结合原位声发射技术，系统研究了航空发动机涡轮导叶用热障涂层材料在CMAS粒子冲蚀条件下的应力演化，裂纹扩展及其失效机制。取得了以下主要研究成果：(1) CMAS粒子冲蚀时接触方式的不同对涂层表面残余应力有显著影响，接触方式不同会导致裂纹产生的方式和类型也有差异。冲蚀速度的增大使接触位置周围产生了不可恢复的形变，改变了YSZ顶层的应力状态，并使界面处的残余应力更加严重，从而诱发涂层的分层失效；(2) 冲蚀角度越大，涂层损伤越严重，在90°时达到最大值，YSZ顶层发生较大程度的破裂，逐渐丧失了其对基体的保护作用。低冲蚀角度下，粒子主要通过切削作用对造成涂层损伤，从样品表面SEM图可以看出，切削处的划痕和沟壑中有微裂纹产生。(3) 冲蚀过程中涂层局部受到压应力，受压的周围区域会发生翘曲，其应力状态类似于涂层的三点弯曲加载，从而借助三点弯的裂纹扩展信号间接分析了冲蚀过程中的裂纹扩展信号。提取了事件计数、振幅、峰值频率和能量四类声发射信号特征参数，并对其进行失效分析，发现声发射信号与加载过程中的应力-应变曲线匹配度很高。基于傅里叶变换和小波分析，得到了基体变形、裂纹萌生和裂纹扩展的频率分布。原位声发射信号来自两个方面：即基材的塑性变形以及涂层中裂纹的萌生和扩展。进一步结合涂层破坏后的横截面观测，发现许多临界裂纹是从涂层的表面开始萌生并向下扩展。而一些主要的裂纹倾向于向粘结层/YSZ顶层和基材/粘结层界面扩展。在该项目资助下，发表SCI论文10篇，申请专利2项，参加国内外会议并作口头报告3次。项目的研究为热障涂层高温冲蚀寿命预测奠定理论基础，并进一步为优化高性能航机导叶用热障涂层的制备工艺提供科学依据。