热-力-化学三场耦合条件下热障涂层TGO层附近裂纹扩展动态行为研究

The thermally grown oxide (TGO) layer is the weak position of the thermal barrier coatings(TBCs). The chemical composition and microstructure of the TGO will be changed dynamically under the thermal-mechanical coupled condition at high temperature. The growth of the TGO and the propagation of cracks around the TGO layer are the most direct causes to induce the failure of the TBCs, while the corresponding mechanism is not completely clear. We have investigated the propagation behavior of the cracks at the inner of the ceramic layer of thermal barrier coatings previously. In fact, the propagation behavior of the cracks near the interface will determine the eventual failure modes of thermal barrier coatings directly. Based on our previous work, the Cohesive Zone Model will be used to simulate the dynamic propagation behavior of the cracks around the TGO under the thermal-mechanical-chemical coupled conditions in this project. The yttria stabilized zirconia(YSZ) thermal barrier coatings will be fabricated via plasma spraying techniques and the thermal shock resistance of the as-sprayed TBCs will be characterized by burner rig test (BRT). The acoustic emission technique combined with the SEM observation of cross-section of the TBCs will be used to further characterize the dynamic characteristics of the cracks around the TGO layer. The propagation behavior of the cracks around the TGO and the mutual effect between the cracks and TGO when the composition and microstructure of the TGO has changed during the high temperature service will be focused on. The investigation results will reveal the influencing mechanism of the cracks propagation around the TGO on the failure patterns of the TBCs under the thermal-mechanical-chemical coupled conditions. This investigation results will lay a theoretical foundation for the interface strengthening techniques and life prediction of the TBCs, as well as further provide the scientific basis for optimizing the processing techniques of TBCs.

热生长氧化物 (TGO) 层是热障涂层的薄弱环节，在高温热力耦合条件下，TGO的成分与微结构处在动态的演化过程中，TGO生长及其附近处的裂纹扩展是引起涂层失效的最直接诱因之一，然而该机制目前尚不十分清楚。我们先前研究了热力耦合条件下热障涂层隔热层内部裂纹扩展行为，但实际上，裂纹在界面处的扩展行为将直接决定涂层最终失效模式。在前期工作基础上，本项目拟采用Cohesive单元子程序研究热-力-化学三场耦合条件下热障涂层TGO层附近裂纹扩展的动态行为。利用强热流密度火焰循环热考核测试等离子喷涂制备的YSZ热障涂层的抗热冲击性能，并结合声发射及涂层截面观测探讨在TGO层成分及微结构演变过程中TGO层处裂纹扩展的动态特征。研究结果将揭示热-力-化学三场耦合条件下TGO层附近裂纹扩展行为对热障涂层失效的影响机制。本研究将为热障涂层界面强化技术奠定理论基础，并进一步为优化热障涂层的制备工艺提供科学依据。

热障涂层作为一类重要的涂层材料，被广泛应用于航空发动机及燃气轮机涡轮叶片上，保护高温合金叶片免受高温氧化、腐蚀、磨损，对于提高航空发动机推重比及燃气轮机热机效率具有重要作用。热障涂层在高温服役条件下，其粘结层与陶瓷层的界面会生成一层热生长氧化物（TGO）层, TGO 层是热障涂层的薄弱环节，在热障涂层高温热力耦合服役条件下，TGO层的成分与微结构处在动态的演化过程中，TGO生长及其附近处的裂纹扩展是引起热障涂层失效的最直接诱因之一。基于目前TGO层附近裂纹扩展引起的涂层失效机制尚不十分清楚，依托本项目开展了热障涂层在热-力-化三场耦合条件下其TGO层内部及附近应力，以及TGO层附近裂纹扩展的研究工作。首先，在不考虑化学场的作用，采用有限元方法计算了在热力耦合条件下热障涂层TGO层内部应力分布以及TGO附近横向裂纹和纵向裂纹的存在对TGO层应力分布的影响。进一步引入化学场作用，考虑TGO在高温服役过程中的生长过程，以及TGO层的形貌结构及化学成分随着服役时间的演变，采用Cohesive单元子程序，结合扩展有限元程序,系统研究了热-力-化学三场耦合条件下热障涂层TGO层附近裂纹扩展的动态行为，与此同时，利用强热流密度火焰循环热考核测试等离子喷涂制备的YSZ热障涂层的抗热冲击性能，并结合原位声发射技术系统研究了涂层在高温服役过程中内部裂纹萌生及扩展的动态行为，根据声发射信号的累积能量，对声发射信号参数进行机器学习，依据涂层应变能释放的断裂力学判据，建立了涂层寿命预测的数学物理模型。研究结果揭示了在热-力-化学三场耦合条件下TGO层附近裂纹扩展行为对热障涂层失效的影响机制。相关研究发表主要代表性SCI论文10篇，申请专利2项，授权专利1项。该研究提出了一种预测涂层高温服役寿命的模型及方法，同时为热障涂层界面强化技术奠定理论基础，并进一步为优化热障涂层的制备工艺提供了科学依据。