Turbine discs in gas-turbine engines always experience high-temperature and high-stress environment. Extensive investigations have been performed towards achieving high performance. Deformation behaviors and degradation factors above normal service temperature are important to be comprehensively understood for further development and optimization of turbine disc superalloys. In this study, the low cycle fatigue behaviors were investigated under total strain amplitude control in U720Li disc superalloys. The results revealed that with the increasing strain, the number of dislocation increased and dislocation configuration transferred from pile-up at the matrix/γ′ precipitates interfaces to penetrating into γ′ precipitates. The great extent of recrystallization was found above the normal service temperature through transmission-EBSD combined with TEM analysis. The low cycle fatigue property above the normal service temperature was weakened to a large extent after recrystallization of small-angle grains formed by the dislocation substructures and movements. Large extent of local recrystallization could also provide much more sites for the crack initiation and propagation.

燃气涡轮发动机中的涡轮盘总是经历高温和高应力的环境。为了实现高性能，已经进行了广泛的研究。为了进一步开发和优化涡轮盘式高温合金，要全面理解高于正常工作温度的变形行为和退化因素，这一点很重要。在这项研究中，研究了U720Li盘式高温合金在总应变幅度控制下的低周疲劳行为。结果表明，随着应变的增加，位错的数量增加，位错构型从基体/γ'沉淀物的堆积转移到渗入γ'沉淀物。通过透射EBSD结合TEM分析发现在正常使用温度以上有很大程度的重结晶。在由位错亚结构和运动形成的小角度晶粒再结晶之后，在正常使用温度以上的低循环疲劳性能在很大程度上减弱了。大量的局部再结晶也可以为裂纹的萌生和扩展提供更多的位置。