应变幅对第二代镍基单晶高温合金DD11在980℃条件下低周疲劳性能的影响

Effects of strain amplitudes on the cyclic deformation behaviour in low cyclic fatigue of a nickel-based single cystal superalloy DD11

摘要:

通过对第二代镍基单晶高温合金DD11在980℃条件下的低周疲劳性能测试及表征,研究了在不同应变幅(△ε/2=0.5~1.2%)对循环应力响应行为和断裂模式的影响。建立了显微组织演变和疲劳行为之间的联系。实验结果表明,该合金发生了循环软化行为并且随着应变幅的提高,循环软化程度降低。γ"的粗化以及垂直于加载轴方向的γ通道加宽有利于位错运动的进行,因此造成了循环软化。当应变幅为0.5%时,位错回复也是造成循环软化的原因。随着应变幅增加至0.8%后,γ"的粗化以及垂直于加载轴方向的γ通道加宽程度降低,位错在两相界面上发生了塞积,造成了循环软化程度的降低。疲劳失效模式从扩展区的正断模式转变为了瞬断区的剪切断裂模式。本研究有利于建立单晶高温合金涡轮叶片疲劳失效模式、循环应力响应行为和组织三者的关系,对涡轮叶片的设计使用具有一定的指导意义。

Abstract:

The cyclic stress responses behaviours and failure modes in the low cyclic fatigue of a nickel-based single crystal superalloys DD11 with [0 0 1] orientation at 980℃ and strain amplitude range of 0.5~1.2% have been investigated. The relationship between deformation microstructure and fatigue behaviours was established. The results showed that cyclic softening occurred and the softening degree decreased with increasing strain amplitude. The coarsening of γ" and the broadening of transverse channels of γ caused the movement of dislocation in the γ channel easily, and cyclic softening was resulted. Moreover, the dislocation recovery occurred at the low strain amplitude which also caused cyclic softening. Since the pilling-up of dislocation at the γ/γ" interfaces occurred as the degree of coarsen of γ" and broaden of transverse channels of γ decreased when the strain amplitude was large than 0.8%, resulting in decreasing in the degree of cyclic softening. The fatigue failure mode changed from normal fracture to shear fracture corresponding to a transferring of the crack stable propagation to the instant fracture. Our result is helpful for building the relationship of various blade fatigue failure modes, cyclic stress response and microstructure deformation under different strain amplitudes. It was benefited for the blade design and the strain amplitude allowable range.