发动机喷管扩张密封片裂纹失效机理研究

航空发动机喷管扩张密封片采用JG4246A金属间化合物高温合金铸造。针对发动机工作过程中产生的扩张密封片裂纹故障，利用视频显微镜、扫描电镜等设备，通过对故障扩张密封片进行宏观检查、断口分析、表面形貌检查、材质分析以及JG4246A材料高温热模拟试验组织对比分析，确定扩张密封片裂纹的性质和失效机理。结果表明:扩张密封片裂纹为以热应力为主引发的疲劳裂纹；组织热模拟试验对比得出，故障部位承受的最高温度已超过JG4246A的许用温度1 200℃，组织中初生γ'相明显回溶，导致性能大幅降低；在冷热交变条件下，故障部位产生较大的热应力梯度，超过了材料的疲劳极限，从而最终导致疲劳开裂。提出提高铸造工艺和优化设计的改进建议。

Cracking Mechanism of Expansion Seal Sheetin Engine Nozzle

The expansion seal sheet in the nozzle of an engine was made of intermetallic compound superalloy JG4246A. It was found to have cracked during service. In order to find out the failure cause, macro and micro observation, material analysis, and over-heating microstructure simulation test were carried out. Results indicate that the cracking mode of the seal sheet is fatigue crack primarily induced by thermal stress. According to the results of the microstructure simulation test, the highest temperature the failure position had experienced exceeded the allowed service temperature, 1 200℃. Obvious redissolution of primary γ' phase caused the significant reduction of performance. In the condition of cold-and-hot alternation, there existed large thermal stress gradient at the failure position, which exceeded the material fatigue strength limit, leading to final fatigue crack. In the end, some measures were proposed to improve the casting technology and optimize the design.