Microstructural evolutions of EK61 superalloy during long-term aging until 1000 h at 700°C and 750°C, respectively, are studied by combination of Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). Impact fracture morphologies after aging for different time are observed by the SEM. The microstructure is found to be relatively stable during aging at 700°C, and the fracture morphologies are characterized by transgranular fracture. At 750°C, the coarsening of γ′ phase leads the reduction of the quantity of dimples, the chainization of carbides on grain boundaries leads to intergranular fracture, and the netting of η phases within grains leads to the formation of lamellar cleavage steps. It is obvious that the destabilization of precipitated phases affects fracture morphology significantly. The relationship between fracture morphology and the microstructure promotes the evaluation of service reliability of EK61 superalloy.

中文翻译：

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EK61高温合金长期时效过程中断裂形貌与显微组织演变的相关性

结合扫描电子显微镜 (SEM) 和透射电子显微镜 (TEM)，研究了 EK61 高温合金在分别在 700°C 和 750°C 下长期时效直至 1000 小时的微观结构演变。通过扫描电镜观察老化不同时间后的冲击断口形貌。700℃时效时显微组织相对稳定，断口形貌以穿晶断口为特征。750℃时，γ′相粗化导致凹坑数量减少，碳化物在晶界的链状化导致晶间断裂，晶粒内η相的网状化导致层状解理台阶的形成。很明显，析出相的失稳对断口形貌有显着影响。