In the present study, the failure of a fifth stage blade of a gas turbine after 500 equivalent operation hours is investigated. After hot gas path inspection, it was found that an airfoil of a blade had been entirely separated from the root. The fracture surface of the root was investigated by stereo and scanning electron microscopes (SEM). Macroscopic investigations of the fracture surface suggested that the fatigue mechanism was responsible for the failure. Visual investigations of blades showed that there were small grooves in each blade root which were not in accordance with the technical maps. Furthermore, the dimensions of the grooves were not identical and each blade had its own groove dimension. The microstructure of the root within and outside of the groove was investigated and the results showed that the morphology, size and distribution of γ׳ precipitates had been changed within the groove area. Moreover, micro-cracks observed in the groove area. According to the obtained results, it was concluded that not only the presences of the groove and micro-cracks (as a potential site for stress concentration) could accelerate crack initiation, but also the microstructural changes within the groove area had a synergistic effect for crack nucleation due to localized softening within the groove.

在本研究中，研究了500个等效运行小时后燃气轮机第五级叶片的故障。经过热气路径检查后，发现叶片的翼型已与根部完全分离。通过立体和扫描电子显微镜（SEM）研究根部的断裂表面。断裂表面的宏观研究表明，疲劳机制是造成破坏的原因。叶片的视觉研究表明，每个叶片根部都有小的凹槽，与技术图不符。此外，凹槽的尺寸不相同，并且每个叶片具有其自己的凹槽尺寸。研究了凹槽内外根部的微观结构，结果表明：凹槽区域内γ׳析出物的大小和分布已经改变。此外，在凹槽区域观察到微裂纹。根据获得的结果，得出的结论是，不仅沟槽和微裂纹（作为应力集中的潜在部位）的存在可以加速裂纹的萌生，而且沟槽区域内的微观结构变化对裂纹具有协同作用。由于凹槽内的局部软化而导致形核。