氧化锆热障涂层铁弹性增韧机制和热老化机理的实验和相场法研究

Thermal barrier coatings (TBC) play a vital role in improving the thermal efficiency of engines. The fracture toughness of the material used in the ceramic coating is an important factor that influences the reliability of the TBC. The metastable tetragonal zirconia ceramics (t'-YSZ，or YSZ) possesses the special ferroelastic toughening mechanism and is the most widely used ceramic layer material currently. In the manufacturing process, typical crystal and defect structures are formed in the YSZ coating. However, there are no corresponding mesoscale studies to quantitatively characterize the fracture mechanism and the ferroelastic toughening effect of the YSZ coating. In addition, with a further increase of the working temperature, the service performance of the YSZ coating is deteriorated by thermal aging. This project aims to develop the coupled phase field models to study the influences of the various microstructural factors such as the crystal orientation, the grain size, the domain structure and the internal defects on the crack propagation behavior and the ferroelastic toughening effect of the YSZ ceramics, by combining numerical simulations with experimental studies. On the basis of that, it is anticipated that the relation between the microstructure and the fracture toughness of the YSZ coating can be established. In the meantime, this project intends to simulate and characterize the thermal aging behavior of YSZ ceramics by combining phase field modelling with experimental studies and investigate how the microstructure influences its performance after thermal aging. It is anticipated that the research results of this project can provide valuable information for the improvement of the service performance of the YSZ coating through microstructure control and through defect morphology control and optimization.

热障涂层（TBC）对于提升发动机热效率起着关键作用。陶瓷层材料的断裂韧性是影响TBC可靠性的重要因素。亚稳态四方相氧化锆(t'-YSZ，简称YSZ)具有特殊的铁弹性增韧机制，是目前应用最广的陶瓷层材料。YSZ涂层在制备时形成特殊的晶体和缺陷结构。目前缺乏相应的介观尺度研究来定量表征YSZ涂层的断裂机理及其铁弹性增韧效应。此外，当工作温度进一步提升时，YSZ涂层的服役性能受热老化问题的困扰。本项目致力于发展相应的耦合相场模型，结合实验研究，探讨晶体取向、晶粒大小、初始畴结构以及内部缺陷等微结构因素对YSZ陶瓷内部裂纹扩展行为及其铁弹性增韧效应的影响，在此基础上，建立陶瓷层断裂韧性与其内部微结构之间的联系；同时，借助相场模拟，结合实验研究，对YSZ陶瓷的热老化行为进行模拟和表征，探讨各微结构因素对其热老化性能的影响；为从微结构调控、缺陷形态控制和优化角度提升YSZ涂层的服役性能提供参考依据。

热障涂层（TBC）能显著降低涡轮叶片表面温度、延长叶片服役寿命、提升发动机热效率。陶瓷层的断裂韧性是影响热障涂层可靠性的关键因素之一。亚稳态四方相氧化锆(t'-YSZ)具有特殊的铁弹性增韧机制，是目前应用最广的TBC陶瓷层材料。发展介观方法来定量表征t'-YSZ的断裂和增韧机理对于TBC的可靠性评估具有重要意义。此外，t'-YSZ涂层的耐受温度受热老化问题制约。尽管学术界开展了大量实验研究，但目前对t'-YSZ的热老化机理仍存在诸多争议，为了揭示相关机理，有必要发展介观尺度方法，从微结构演化角度对t'-YSZ的热老化行为进行定量表征。.在基金资助下，研究团队构造了模拟t'-YSZ陶瓷铁弹畴翻转以及氧化锆c-t'相变、t-m相变的相场模型，在此基础上，构造了可同时模拟裂纹扩展以及铁弹畴翻转/相变过程的耦合相场模型。利用所发展的耦合相场模型，团队研究了单晶单畴t'-YSZ、单晶多畴t'-YSZ、多晶单畴t'-YSZ、多晶多畴t'-YSZ以及t相氧化锆的裂纹扩展行为，探讨了晶体取向、晶界、初始畴结构以及反相畴界等因素对氧化锆断裂行为的影响，通过计算能量耗散率定量表征了t'-YSZ的铁弹增韧效应以及t相氧化锆的相变增韧效应。同时，团队构造了模拟t'-YSZ热老化行为的扩散-相变耦合相场模型，利用所发展的相场模型研究了单晶单畴t'-YSZ、单晶多畴t'-YSZ以及多晶多畴t'-YSZ的热老化行为，探讨了稳定剂浓度、初始畴结构和反相畴界等微结构因素对t'-YSZ热老化行为的影响，对实验中观测到的热老化现象给出了机理性解释。本项目的研究增进了对t'-YSZ断裂机理和热老化机理的理解，为热障涂层的断裂性能评估以及服役性能演变机理的表征提供了介观尺度模拟方法。