纳米结构热障涂层的损伤灾变实验及机理研究

Thermal barrier coatings have wide application in aerospace, marine, mechanical fields, etc. For example, for firebox of rocket engines worked in high temperature environment, the ZrO2 coatings of several hundred microns are sprayed or deposited on the Ni-based alloy substrates as thermal protection. The interface between the coatings and the substrates will fracture when the parts experience thermal shock, bending loading due to the interface mismatch of two materials. Once the coatings spall, the alloy parts will failure soon. The quality and life of the related parts are improved by changing microstructure, size and fabrication process of the coatings and the alloys. Nanostructured coatings may appear different mechanical behavior compared to the conventional coatings due to the smaller microstructure scale, related study on their mechanical behavior is few. To study damage and failure behavior of nanostructured ceramic coatings/alloy substrates systems under thermal, mechanical loading not only is significant in guiding design and application of coating systems, but also provides an appropriate platform for developing micro/nanoscale mechanical, interface mechanical theory, and elastic brittle damage model. In this project, damage and catastrophic failure characteristics and mechanism of several kinds of micro/nanostructured ceramic coatings/alloy substrates systems will be studied systematically by performing in situ 3-point bending and 4-point bending experiments and checking crack evolution. A general brittle damage model will be developed based on the Taylor’s expansion and the experimental results, a new damage parameter will be proposed, and the physical meaning of the related damage parameter will be revealed combining with the microstructure and nanoscale interface thermodynamics. Moreover, the model will be used to study damage and failure of the coatings under thermal shock to develop thermal-mechanical damage relation and to provide reference for designing coatings and failure prediction.

热障涂层在航天等许多领域有重要应用，如高温下服役的火箭发动机燃烧室、涡轮发动机叶片等，一旦涂层开裂、剥落，暴露在高温下的金属基底将很快失效，故该体系在各种力、热载荷下的失效行为广受关注，而其中纳米结构涂层由于较小的微结构尺度可能展现出不同的行为，相关研究却较少。对纳米结构热障涂层的损伤失效行为研究，不仅对实际应用具有借鉴意义，而且为发展薄膜及界面力学、微纳米多尺度力学以及弹脆性涂层损伤力学提供了契机。本项目基于热力等效思想，拟通过开展微纳米结构涂层样品的原位四点弯及三点弯系统实验，实时考察裂纹演化，定义损伤参量，结合控制变量（如应力）的Taylor 展开，发展弹脆性涂层的损伤灾变模型；并根据纳米结构涂层的损伤失效特征，结合纳米表界面热力学模型刻画纳米结构涂层的损伤失效机制；最后将之应用于研究涂层在热震及热冲击载荷下的损伤失效行为，建立热-力损伤失效关联，以期为涂层设计及破坏预测提供依据。

热障涂层在航空航天等许多领域有重要应用，如高温下服役的火箭发动机燃烧室、涡轮发动机叶片等，一旦涂层损伤开裂、剥落，暴露在高温下的金属基底将很快失效，因此研究涂层结构在力、热载荷下的损伤规律，尤其灾变失效研究具有重要意义。其中纳米结构涂层由于减小的微结构尺度展现出不同的力学性能，其损伤失效有什么特点，研究这一问题为从微结构特征到宏观损伤的跨尺度关联研究提供了载体。本项目通过设计并开展微纳米结构涂层样品的原位弯曲实验及模拟、以及热震实验等，实时考察了裂纹演化，定义了损伤变量，结合控制变量（如主控应力、温度、循环次数等）的Taylor展开，发展了弹脆性涂层的损伤灾变模型；发现实验结果与理论一致，损伤演化满足统一的幂次规律。研究表明厚涂层比薄涂层损伤较快、纳米结构厚涂层比微米结构涂层损伤较慢、弯曲载荷下损伤比热载荷下损伤较快、高温拉伸比室温拉伸损伤较快等；创新提出了表征损伤速率的损伤系数，揭示了它的能量机制。损伤模型可定量表征涂层结构的损伤与其几何、微结构尺度、界面强韧性、加载条件等的相关性。项目研究为涂层相关部件的设计及破坏预测与应用可靠性提供了基础依据。