含Ru镍基单晶高温合金塑性变形诱发应变局部化与疲劳性能退化微观机制研究

Plastic deformation induced strain localization is the main reason that lead to low cycle fatigue (LCF) performance degradation of the Ni-base single crystal superalloys. In order to obtain an in-deepth understanding of the relationship between strain localization and LCF performance degradation, a comprehensive method will be used to analyze the microstructures, such as transmission electron microscopy (TEM) et al.. Correlations between the main strengthen elements distribution, type of solidification defects, dislocation configurations, interactions between dislcoation movements and γ′ phase, configurations of stacking faults in γ and γ′ phases and strain localization will be firstly investigated under different LCF conditions including interrupt tests. The effects of Ru additions on LCF deformation mechanisms will be studied in detail to clarify the role of Ru additions during strain localization. Based on these studies mentioned above, the initiation mechnisms of strain localization are researched and the site of strain localization prefer to appear can be determined. Secondly, the critical conditions of microcracks initiation which caused by the stress filed of strain localization under different deformation conditions will be discussed and the dependence of microcracks formation on the stress filed of strain localization also will be revealed by considering the relationships between strain localization stress filed and intiation of the microcracks. Finally, the intrinsic correlation between strain localization and LCF performance degradation will be determined, providing a basis for microstructure control and fatigue damage prediction of advanced Ni-base single crystal superalloys.

塑性变形诱发应变局部化是镍基单晶高温合金低周疲劳性能退化的主要原因。为深入理解应变局部化与合金疲劳性能退化微观机制，本项目拟借助TEM等材料分析测试手段，首先探究不同疲劳条件下（包括中断实验）镍基单晶合金主要强化元素分布、凝固缺陷类型、位错组态、位错与γ′相的交互作用形式、γ和γ′相中层错的组态等与应变局部化形成的关系；研究Ru的添加对疲劳微观变形机制的影响，阐明Ru在单晶合金应变局部化过程的作用；基于以上研究，探明应变局部化萌生的微观机制，明确其优先起源的位置。其次，研究应变局部化应力场与裂纹萌生的关系，探讨不同变形条件下应变局部化应力场导致微裂纹萌生的临界条件，揭示微裂纹萌生与应变局部化应力场的依赖关系。最后，明确应变局部化与低周疲劳性能退化的内在关联，为先进镍基单晶高温合金组织结构调控与疲劳失效预测提供理论依据。

航空发动机的涡轮叶片和导向叶片等在飞机起飞和降落的过程中，要经历热应力变化以及机械应力变化，构件失效常以低周疲劳（Low cycle fatigue，LCF）断裂的形式出现。而塑性变形诱发的应变局部化是导致镍基单晶高温合金低周疲劳性能退化的主要原因。本项目以无Ru和含Ru镍基单晶高温合金为研究对象，主要研究了两种合金不同温度以及不同应变幅下的低周疲劳行为，探索了Ru的添加对合金疲劳性能以及应变局部化的影响。.在低温疲劳变形过程中，含Ru合金的疲劳寿命较长，主要是因为两种合金在位错运动过程中开启了不同的滑移系，造成合金的滑移开裂方向以及开裂方式不同，从而使得两种合金的疲劳寿命存在差异；在中温区域疲劳变形时，由于含Ru合金的层错能更低，合金基体和析出相中形成的扩展位错明显强化了合金，使得含Ru合金的性能更为优异；建立了两种合金在高温时的原子结构简化模型，揭示了温度和Ru含量对合金内部畴界能和层错能的影响，最终导致了合金疲劳寿命上的宏观差异。随着应变幅的增加，合金的疲劳寿命逐渐降低；在900℃不同应变幅条件下，氧化损伤是合金疲劳失效的主要原因。设计了低周疲劳模型，模拟了低周疲劳时应变局部化的演化过程，研究表明第一个循环周次后合金即出现轻微的应变局部化，每一个循环周次后合金都会产生一定的应力及应变累积，从而加速应变局部化的形成，最终导致样品断裂失效。.通过以上研究，揭示了合金应变局部与疲劳损伤的内在关系，为镍基单晶高温合金疲劳性能的可靠性评价提供了依据，同时对评估单晶叶片的实际服役具有重要意义。