对一种新型镍基单晶高温合金在不同应变幅(0.7%～1.2%)下进行760℃高温低周疲劳试验,探讨了应变幅对合金低周疲劳行为的影响,分析了其疲劳塑性变形特点和疲劳断裂机制。结果表明:随着应变幅的增加,合金的低周疲劳寿命缩短,循环软化程度显著降低;当应变幅为0.7%,0.8%时,位错在与应力轴垂直的基体通道中的平面滑移及位错滑移带的形成是疲劳变形的主要方式,疲劳裂纹起源于合金内部缩孔处,断口形貌的主要特征是疲劳解理台阶和撕裂棱,断裂机制为解理断裂;当应变幅为1.0%,1.2%时,位错剪切γ'相粒子及层错的出现是合金变形的主要特征,裂纹起源于合金表面应力集中的滑移带或显微疏松位置,裂纹在{111}滑移面上沿〈110〉方向扩展,断口形貌的主要特征是锯齿台阶和河流花样,断裂机制为解理断裂。

760℃ high temperature low cycle fatigue tests were carried out on a new nickel-based single crystal superalloy at different strain amplitudes (0.7%-1.2%). The effect of strain amplitude on low cycle fatigue behavior of the alloy was discussed, and the fatigue plastic deformation characteristics and fatigue fracture mechanism were analyzed. The results show that low cycle lifetime decreased with increasing strain amplitude, and the degree of cyclic softening was significantly reduced. At the strain amplitudes of 0.7% and 0.8%, the plane slip of dislocation in the matrix channel perpendicular to the stress axis and the formation of dislocation slip band were the main modes of fatigue deformation; the fatigue cracks initiated at the shrinkage cavity inside the alloy; the fracture morphology was mainly characterized by fatigue cleavage step and tearing edge, and the fracture mechanism was cleavage fracture. At the strain amplitudes of 1.0% and 1.2%, the main characteristic of alloy deformation was the occurrence of dislocation shearing γ' particle and lamination; the cracks initiated at the stress concentrated slip band or micropore on the alloy surface, and the cracks propagated along the orientation 〈110〉 on {111} slip plane; the fracture morphology was mainly characterized by sawtooth steps and river pattern, and the fracture mechanism was cleavage fracture.