High-temperature fatigue property of Ni-based GH4720Li superalloy at 550 °C has been investigated at maximum strain from 0.8% to 1.1%. Microstructural characterization and oxidation behavior of superalloy during high-temperature fatigue have been analyzed by transmission electron microscopy and scanning transmission electron microscopy. The results show that a stable response following a slight cyclic hardening during initial cycles was revealed at the maximum strain from 0.8% to 1.0%. The stable response decreased with an increase in maximum strain. Continuous cyclic hardening was observed at the maximum strain of 1.1%. There is difference in dislocation substructures between primary γ′ precipitates and γ grains. Dislocation cell and mechanical twin were formed in the interior of primary γ′ precipitates and γ grains. The primary γ′ precipitate interface would migrate toward the interior of primary γ′ precipitates along twin boundaries, leading to instability of primary γ′ precipitates. The secondary γ′ depleted zone was distinctly generated near the surface due to the decomposition of secondary γ′ precipitates. The crack initiation and propagation during high-temperature fatigue were found inside the secondary γ′ depleted zone. The primary γ′ precipitates could effectively hinder the crack propagation. Al-rich oxide films (Al₂O₃) were initially produced at crack tips, because the rate of diffusion of Al was relatively higher than that of other elements at crack tips.

Ni基GH4720Li高温合金在550°C时的最大疲劳应变为0.8％至1.1％，研究了高温疲劳特性。通过透射电子显微镜和扫描透射电子显微镜分析了高温疲劳过程中高温合金的组织结构和氧化行为。结果表明，在初始循环中的轻微循环硬化之后，在最大应变从0.8％到1.0％时显示出稳定的响应。随着最大应变的增加，稳定响应降低。在1.1％的最大应变下观察到连续循环硬化。初生的γ'析出物和γ晶粒之间的位错亚结构存在差异。在主要的γ'析出物和γ晶粒内部形成了位错单元和机械孪晶。初始γ'沉淀物界面将沿孪生边界向初始γ'沉淀物内部迁移，从而导致初始γ'沉淀物不稳定。由于次生γ'沉淀物的分解，次生γ'耗尽区在表面附近明显产生。在次级γ'耗尽区内部发现了高​​温疲劳过程中的裂纹萌生和扩展。最初的γ'沉淀物可以有效地阻止裂纹扩展。富铝氧化膜 在次级γ'耗尽区内部发现了高​​温疲劳过程中的裂纹萌生和扩展。最初的γ'沉淀物可以有效地阻止裂纹扩展。富铝氧化膜 在次级γ'耗尽区内部发现了高​​温疲劳过程中的裂纹萌生和扩展。最初的γ'沉淀物可以有效地阻止裂纹扩展。富铝氧化膜最初在裂纹尖端产生₂ O ₃），因为Al的扩散速率相对高于裂纹尖端其他元素的扩散速率。