过热超温对镍基单晶涡轮叶片蠕变损伤及寿命的影响研究

Overtemperature is an inevitable abnormal service condition in the nickel-base single crystal superalloy turbine blade. It can be divided into overheating and ablation. The damage of ablation is visible to naked eyes. The blade must be immediately replaced once the ablation damage occurs. In contrast, the damage of overheating is less detectable and more harmful to the blade. The influence of overheating on the creep behavior of the turbine blade is very complex and has not been clarified yet. In the present project, the overheating effect on the creep behavior of the aeroengine turbine blade will be studied with the consideration of the specialty of the material and the service conditions. Experiments will be performed considering various overheating factors, such as temprature, duration and opportunity. With the consideration of the material microstructure and its evolution, the creep damage mechanism will be revealed by both experimental and theoretical analysis. Dislocation dynamics modelling and the phase field methods will be used. The micro controlling factors will be quantitatively extracted as representative variables to describe microstructure evolutions influenced by the overheating. Based on the failure mechanism, a life model will be established, which could describe the overheating effect under service loading conditions. Finally, research achievements will be applied to the overheating analysis of nickel-base single crystal superalloy turbine blade. A creep life evaluation method will be established. The research of this project can provide the evaluation method for the creep damage and life of the turbine blade considering the overheating-dependent influence. And it also can ensure the safety and economic operation of the blade. The model and method developed can be used directly in engineering applications. Therefore, this study not only has important scientific value but also has engineering significance.

超温分为过热和过烧，是镍基单晶涡轮叶片服役过程中不可避免的非正常工况。其中过烧叶片外表特征显著且必须马上做更换处理，而过热未达到材料的固相线，叶片外观无明显损伤特征，但会对材料性能产生复杂影响，导致断裂故障。迄今，国内外就过热超温对蠕变损伤影响的机理和规律缺乏系统的试验和理论研究，缺少定量的评估方法。本项目针对镍基单晶涡轮叶片的材料特点和服役工况，从材料的细微观组织结构及其演化规律出发，开展过热超温宏观与细观试验，结合分子动力学、相场理论与晶体塑性理论的细观模拟分析，研究过热超温状态（超温温度、超温时间、超温时刻）对材料蠕变性能影响的细微观机理；提取损伤演化过程中的特征量，探索过热超温对蠕变寿命的影响规律并建立模型；将研究成果应用于叶片超温分析中，提出过热超温影响蠕变损伤的评估方法。本项目为过热超温单晶叶片提供寿命的定量评定方法，具有重大科学和工程意义。

航空发动机在服役过程中，经常发生单发失效、追机与逃逸等非常规工况，在这些工况中由于供油量过多等原因导致发生过富油燃烧，致使涡轮后排气温度超出规定限制值，即发生超温现象。超温过程常伴随着材料组织性能劣化、构件变形增大等，以至涡轮叶片强度和寿命降低，甚至发生断裂故障。迄今，超温对蠕变损伤影响的机理缺乏系统研究。.本项目主要研究内容为开展镍基单晶合金宏观与细观过热超温试验，结合分子动力学和位错动力学、相场理论与晶体塑性理论，研究过热超温状态对蠕变损伤演化的影响机理；提取损伤演化过程中的特征量，研究建立过热超温对蠕变寿命的影响模型；并将研究成果应用于涡轮叶片超温分析中，提出过热超温影响蠕变寿命的评估方法。.研究结果表明，当前期蠕变时间分别为5h，10h和15h时，超温试验的蠕变寿命分别为等温寿命的80.12%、65.38%和59.32%，即前期蠕变时间越长，蠕变寿命减短。同时超温阶段的蠕变应变呈增长趋势，分别为0.649%、0.658%和0.665%，且与前期蠕变时间呈指数关系。超温后蠕变速率也显著增大，依次为前期速率的1.15, 2.55和3.85倍。基于硬化机制、γ基体通道的动态演化及位错密度的演化，提出了基于晶体塑性理论的超温蠕变模型，该模型可以较好地捕捉到超温试验中的应变瞬时跳跃、应变演化及应变速率的变化，与试验曲线间误差控制在8%以内。.本研究将增加对国产镍基单晶涡轮叶片在超温蠕变工况下的损伤机理的基本认识，提出过热超温评估方法应用到具体涡轮单晶叶片分析之中，不仅可以尽量避免灾难性事故的发生，减少不确定因素，而且可充分利用材料性能储备并且安全地确定涡轮单晶叶片强度和寿命，从而推动国产发动机的发展和单晶材料的应用。本研究为叶片在服役过程中提供过热超温评定方法，可以确保叶片的安全和经济运行，具有重大科学和工程意义。