Creep-fatigue interaction is identified as a primary failure mode for components operating under high temperatures. As operational durations extend, this interaction not only alters the material's microstructures but also initiates a gradual degradation in mechanical properties, significantly impacting its deformation and damage behaviors. In this work, the dynamic microstructural evolution of GH4169 superalloy during creep-fatigue was elucidated via qualitative characterization, and damage level evaluation method was subsequently developed by bridging microstructure degradation to mechanical property degradation. Creep-fatigue tests were performed at 650 °C with various tensile holding times and were interrupted at lifetime fractions of 10 %, 50 % and 80 % for further analysis and tensile evaluations. Results revealed that the prolonged exposure to holding times induced the coarsening of precipitates alongside an increase in low-angle grain boundaries, culminating a reduction in creep-fatigue strength. The development of voids and cracks exacerbated the degradation of elongation, leading to a hybrid fracture mode encompassing both intergranular and transgranular cracking paths. Synthesizing microstructural evolutions to qualitatively categorize diverse degradation levels imparted a robust physical basis for damage evaluation. A mapping model was established to correlate the average kernel average misorientation (micro-degradation indicator) with the tensile plastic strain energy density (macro-degradation indicator). The damage level evaluation method was endowed with quantitative metrics utilizing this model, and its generality was additionally validated in P92 steel. This work offers an insight into the quantitative damage evaluations of creep-fatigue-induced degradations in materials, thereby providing a theoretical basis for the development of operation management and inspection plans of components.

中文翻译：

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基于微观结构演化与力学性能退化关系的蠕变疲劳损伤水平评估


蠕变疲劳相互作用被认为是在高温下运行的部件的主要失效模式。随着运行时间的延长，这种相互作用不仅会改变材料的微观结构，还会导致机械性能逐渐下降，从而显着影响其变形和损坏行为。在这项工作中，通过定性表征阐明了 GH4169 高温合金在蠕变疲劳过程中的动态微观结构演化，并随后开发了将微观结构退化与机械性能退化联系起来的损伤水平评估方法。蠕变疲劳测试在 650 °C 下进行，具有不同的拉伸保持时间，并在寿命分数为 10%、50% 和 80% 时中断，以进行进一步分析和拉伸评估。结果表明，长时间的保温会导致析出物粗化，同时小角度晶界增加，最终导致蠕变疲劳强度降低。空隙和裂纹的发展加剧了伸长率的下降，导致包括沿晶和沿晶裂纹路径的混合断裂模式。综合微观结构演化来定性分类不同的退化水平，为损伤评估提供了坚实的物理基础。建立了映射模型，将平均核平均取向差（微观降解指标）与拉伸塑性应变能密度（宏观降解指标）相关联。利用该模型赋予损伤水平评估方法定量的指标，并在P92钢中进一步验证了其通用性。 这项工作提供了对蠕变疲劳引起的材料退化的定量损伤评估的见解，从而为部件的运行管理和检查计划的制定提供了理论基础。