接触晶向和温度相关的镍基单晶合金微动疲劳损伤机理及寿命评估模型

The dovetail contact between the aero-engine turbine blade and disk is a typical fretting fatigue condition, and fretting fatigue can cause the blade to break from the root which will lead to engine failure. Nickel-based single crystal superalloys(NBSX) have been widely used in turbine blade manufacturing due to its excellent properties. However, the uncontrolled second crystal orientation may cause the contact areas of the dovetail joints to have different contact crystal orientations, which in turn leads to differences in fretting fatigue properties. Therefore, it is of great theoretical and engineering value to explore the influence of contact crystal orientation and temperature on the fretting fatigue of NBSX, observe the evolution mechanism and crack behavior of fretting fatigue damage, and establish an effective life prediction model. We will conduct fretting fatigue experiments with different contact crystal orientations and temperatures, combined with in-situ observation techniques, to reveal the damage evolution process and crack initiation and propagation modes. We will explore the effects of contact crystal orientation, temperatures and material defects on fretting fatigue. Crystallographic damage will be analysed and the damage parameter will be established. The crystal plastic constitutive model will be improved to characterize the damage evolution. Based on the multi-axis stress critical plane method, a reliable fretting fatigue life model will be established based on the damage parameters to construct the constitutive properties of the material. The micro-macro-scale analysis method of damage parameter-lifetime provides technical support for fault analysis and life assessment of our aero-engines.

发动机叶片与涡轮盘之间的榫槽接触是一种典型的微动疲劳工况，微动疲劳会导致叶片从根部发生断裂进而造成发动机故障。镍基单晶合金由于具有优异的性能，已经广泛被应用于涡轮叶片制造。然而，不加控制的第二晶向使得榫槽接触部位可能具有不同的接触晶向，进而导致微动疲劳性能的不同。因此，探究接触晶向和温度对于镍基单晶微动疲劳的影响、观测微动疲劳损伤演化机制和裂纹行为、建立有效的寿命评估模型具有重要的理论和工程价值。开展接触晶向不同的微动疲劳实验，结合原位观测技术，揭示损伤演化过程和裂纹萌生、扩展模式，探究各因素对于微动疲劳的影响；使用单晶合金的晶体学损伤分析方法提取损伤参量，建立能够表征损伤演化的晶体塑性本构模型；基于多轴应力的临界平面法等分析方法，基于损伤参量建立起可靠的微动疲劳寿命模型，从而搭建材料本构性能-损伤参量-寿命的微宏观跨尺度分析方法，为我国航空发动机的故障分析和寿命评估提供技术支撑。

航空发动机的涡轮叶片和轮盘之间的榫头-榫槽接触是典型的微动疲劳工况，微动疲劳能够使叶片发生断裂，导致航空发动机过早失效。具有优秀高温力学性能的镍基单晶合金已经被广泛用于涡轮叶片的制造，但由于其各向异性，叶片制造过程中不加控制的第二晶向可能会影响叶片的微动疲劳性能。此次研究中，设计并实现了微动疲劳实验装置，开展了不同晶向和温度下镍基单晶试件的微动疲劳寿命测试、损伤演化原位观测以及晶体塑性有限元模拟，结果表明晶体取向不同的试件的微动疲劳寿命具有显著差异，第二晶向为[110]的试样的微动疲劳寿命比第二晶向为[010]的试样更长，当温度从600℃上升到700℃时，试样的微动疲劳寿命降低。对损伤后的试件进行了电子背散射衍射表征，取向差和几何必需位错密度的分析结果表明接触区域发生了显著的塑性变形，具有不同晶体取向的镍基单晶合金试样的主导滑移系具有显著差异。基于实验得到的寿命数据和模拟计算得到的损伤参量，在多种临界平面参数中，基于能量的CCB参数表现出最高的预测效果，建立了考虑温度和接触晶向的微动疲劳寿命评估模型。此次研究揭示了镍基单晶合金的微动疲劳损伤机理，建立了微动疲劳失效机理与宏观性能的关联，为榫连接微动疲劳的寿命评估和失效分析提供了基础。