氮化硅陶瓷高温表界面能理论研究与断裂机理分析

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.

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。

现役高端燃气涡轮发动机的工作温度已达到了高温合金的使用极限，目前世界各国都在积极开展用高温结构陶瓷替代金属材料制造冷发动机方面的工作。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。本项目基于固体物理，考虑陶瓷材料的热力学过程，并结合固体材料的温度相关性理论拉伸强度和理论剪切强度模型，建立了考虑热分解和相变影响的材料温度相关性表面能和晶界能理论模型。采用Vickers压痕法测试了Si3N4陶瓷材料从室温到1200℃之间的断裂性能，基于微观断裂力学分析了裂纹扩展行为，表征了室温和高温下的裂纹偏转角分布和裂纹穿沿晶比例。分析了Si3N4陶瓷材料的表面能、晶界能、Vickers硬度、杨氏模量和断裂韧性的温度相关性，阐述了材料断裂韧性在韧脆转变温度之后升高的原因。将断裂力学分析模型和Fortran程序相结合，开展了Si3N4陶瓷材料裂纹扩展分析。通过改变晶界能强弱，并结合前述分析，讨论了影响Si3N4陶瓷材料高温断裂性能的主要因素。研究表明表面能和晶界能具有相似的温度相关性，与前期不考虑相变影响给出的理论结果的上限更接近。残余热应力在晶界附近处于拉应力状态，减弱了晶界的结合强度，降低了裂纹的沿晶阻力。晶界相在高温下可能软化并对断裂性能产生较大影响，沿晶临界能量释放率是影响Si3N4陶瓷材料高温断裂行为的重要参量。本项目研究成果有望丰富和发展高温强度理论和断裂力学，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。