Low-cycle fatigue (LCF) behaviors of a second-generation nickel-based single-crystal superalloys with [001] orientation at 760 °C have been investigated. Different strain amplitudes were introduced to investigate the creep-fatigue effects. The LCF life of none tensile holding (NTH) was higher than that of the 60-s tensile hold (TH) at any strain amplitude. As the strain amplitude was 0.7%, the stacking and cross-slip dislocations appeared together at the γ/γ’ coherent microstructure in both TH and NTH specimens. At the strain amplitude of 0.9%, plenty of the cross-slip dislocations appeared in γ channel and other dislocations were stacking at γ/γ’ interfaces. However, the SFs still appeared in γ’ phase with 60-s TH which caused cyclic softening. As the strain amplitude increased up to 1.2%, the dislocations are piling up at the γ/γ’ interfaces and cutting through the γ’ phase in both TH and NTH tests, which caused cyclic hardening. The influences of strain amplitude and holding time were complicated. Different stress response behaviors occurred in different loading conditions. The surface characteristic and fracture mechanism were observed by scanning electron microscopy. This result is helpful for building the relationship of various blade fatigue failure modes, cyclic stress response and microstructure deformation under different strain amplitudes.

中文翻译：

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760°C下第二代镍基单晶高温合金的低循环疲劳和蠕变疲劳行为

已经研究了在760°C下具有[001]取向的第二代镍基单晶高温合金的低周疲劳（LCF）行为。引入了不同的应变幅度来研究蠕变疲劳效应。在任何应变振幅下，无拉伸保持力（NTH）的LCF寿命均高于60-s拉伸保持力（TH）的LCF寿命。当应变幅度为0.7％时，TH和NTH样品的γ/γ'相干组织中同时出现堆积和错位错位。在应变幅度为0.9％时，在γ通道中出现了大量的错滑错位，其他位错则堆积在γ/γ'界面上。但是，SF仍以60 s TH的γ'相出现，引起循环软化。随着应变幅度增加到1.2％，在TH和NTH测试中，位错堆积在γ/γ'界面并贯穿γ'相，从而导致循环硬化。应变幅度和保持时间的影响是复杂的。在不同的载荷条件下会发生不同的应力响应行为。通过扫描电子显微镜观察其表面特性和断裂机理。这一结果有助于建立各种叶片疲劳失效模式，循环应力响应和不同应变幅度下的微观结构变形之间的关系。通过扫描电子显微镜观察其表面特性和断裂机理。这一结果有助于建立各种叶片疲劳失效模式，循环应力响应和不同应变幅度下的微观结构变形之间的关系。通过扫描电子显微镜观察其表面特性和断裂机理。这一结果有助于建立各种叶片疲劳失效模式，循环应力响应和不同应变幅度下的微观结构变形之间的关系。