单晶镍基高温合金的缺口疲劳行为和多轴疲劳寿命预测研究

The fatigue behavior of single crystal nickel base superalloy is one of the major ingredients in the failure and destruction of advanced aero-engine turbine blade. Firstly, the low cycle fatigue tests are carried out on smooth specimen and notched specimen of single crystal alloy DD6 at elevated temperatures in order to reveal the characters of fatigue behaviors. Secondly,the advanced anisotropic constitutive model is employed to analyze the stress and strain field near the notch, which could quantitatively determine the stress and strain distribution and concentration. Thirdly, the multiaxial fatigue life method considering the anisotropy of DD6 is established to predict the fatigue life of the notched specimen, which will be the new way of analyzing the turbine blade life. Lastly, the fractured specimen and microstructure evolution during the tests is observed to identify the failure mechanism of single crystal DD6. In brief, based on the high temperature experiments, constitutive modeling, life predication and the observation of failure features, the effects of temperatures, loadings, crystal orientations and notch types on the low cycle fatigue behavior and failure mechanisms of single crystal alloy DD6 are studied. The research results will lay the foundation of suggesting a new way in structure design, strength evaluation and life predication for single crystal turbine blade.

单晶镍基高温合金的疲劳行为是导致先进航空发动机涡轮叶片失效和破坏的主要因素之一。本项目拟在单晶合金DD6材料和缺口构件两个级别上分别开展高温低循环疲劳试验研究，揭示合金的宏观力学行为特征。采用先进的各向异性本构模型对缺口构件局部应力/应变场进行有限元计算和分析，定量确定缺口附近区域处应力/应变的分布规律和集中程度。建立多轴应力状态下且考虑单晶合金各向异性特征的疲劳寿命模型对缺口构件进行寿命预测，形成新的涡轮叶片寿命分析技术和方法。对试样断口进行微观观测，探明高温裂纹萌生与断裂的微观机制。基于以上单晶合金DD6的高温试验、本构建模、寿命预测和断口观测等研究，揭示不同温度、不同载荷形式、不同晶体取向以及不同缺口形式等因素对材料及缺口构件低循环疲劳行为和失效机理的影响规律。项目研究成果将为建立单晶合金涡轮叶片结构设计、强度评价和寿命预测的新方法提供有力的基础支持。

DD6单晶合金，一种单晶镍基高温材料广泛应用于制造先进航空发动机的涡轮转子叶片，具有较好的抗高温、抗氧化、抗疲劳和抗持久/蠕变等性能，是国内目前综合力学性能最优的高温合金之一。课题研究内容主要是围绕DD6单晶合金的高温疲劳失效问题展开的。首先，通过开展高温疲劳试验已定量确定DD6单晶合金的高温疲劳行为和寿命，也已定性分析了其疲劳断裂失效机理。其次，采用考虑材料各向异性的先进Chaboche统一本构模型对DD6单晶合金材料及缺口构件进行特定载荷下的有限元计算和模拟，计算数据与试验数据吻合地很好，模拟精度较高，可用于复杂结构件的有限元计算且预测精度高。然后，采用改进的且考虑Hill屈服准则的各向异性寿命模型对DD6单晶合金材料及缺口构件的疲劳寿命进行预测，预测精度较高，预测寿命均位于试验寿命的±2倍分散带以内。最后，通过开展DD6单晶合金原位疲劳试验，探明了高温裂纹萌生与断裂的微观失效机制。总之，通过以上对DD6单晶合金高温疲劳断裂试验、原位疲劳试验、本构建模、寿命预测和断裂失效机理的系统研究，为DD6单晶合金的进一步工程化应用奠定了坚实的基础。