氮化硅陶瓷高温表界面能理论研究与断裂机理分析

陶瓷材料的高温断裂行为对其微观结构十分敏感，然而，由于缺乏有效的陶瓷材料高温表界面能预测方法，已有理论和数值计算方法在研究陶瓷材料的高温断裂行为时并不能很好地考虑微观结构的影响。本项目将重点开展陶瓷材料温度相关性表面能和晶界能理论建模方面的研究，解决陶瓷材料高温表界面能等参量预测难的问题，理论预测Si3N4陶瓷材料的高温表界面能；开展高温压痕实验获得Si3N4陶瓷材料的高温力学参数和高温断裂参数；根据压痕附近的真实微观结构，基于微观断裂力学，建立数值分析模型，采用理论获得的高温表界面能和实验获得的高温力学参数，预测Si3N4陶瓷材料的高温断裂行为，计算得到的裂纹扩展路径信息与实验结果对比，验证数值分析模型，然后通过控制变量法，研究影响Si3N4陶瓷材料高温断裂行为与破坏模式的主要参量，揭示其高温断裂机理，为Si3N4陶瓷材料在燃气涡轮发动机中的应用和安全可靠性评估提供理论基础和技术支撑。

The high-temperature fracture behavior of ceramics is susceptible to the microscopic structures. However, the existing theoretical and numerical methods for studying the facture behavior of ceramics at elevated temperatures cannot include the effects of microscopic structures well because that the surface and interfacial energies of ceramics cannot be determined accurately. In this project, taking silicon nitride (Si3N4) ceramics as an example, the temperature-dependent theoretical models for surface energy and grain boundary energy are established based on the classical theories for crystal deformation and the temperature-dependent theories for ideal tensile strength and ideal shear strength. The mechanical and fracture properties of Si3N4 ceramics at elevated temperatures are measured by Vickers indentation technique. A numerical analysis model is established according to the microscopic structures near the Vickers indentation based on the micromechanics. The fracture behavior of Si3N4 ceramics at high temperatures is predicted by this model using the surface and interfacial energies from the theories and mechanical properties from the experiment. The crack path given by the numerical analysis model is compared with that from the experiment to verify the accuracy of the model. The main factors affecting the high-temperature fracture behavior and fracture modes of Si3N4 ceramics are studied by controlling variables method to reveal the fracture mechanisms. This project is a cutting-edge basic research. The achievement will lay the groundwork for developing the high-temperature strength theory and fracture mechanics. At the same time, it can also provide both theoretical basis and technical guidance for the design, application, and evaluation of the reliability of Si3N4 ceramics in the gas turbine engines.