Based on the tensile stress-dominated (strain ratio,$\mathrm{R}={\mathrm{\epsilon }}_{\mathit{min}}/{\mathrm{\epsilon }}_{\mathit{max}}=0$) and compressive stress-dominated (R = ∞) low-cycle fatigue (LCF) of a first-generation directionally solidified Ni-based superalloy DZ445 at 900 °C, the paper investigated the contribution of tensile stress and compressive stress to the damage during LCF and creep-fatigue deformation. The results demonstrated that the fatigue life in the case of tensile stress-dominated LCF is about half of that in compressive stress-dominated LCF. Under the case of tensile stress-dominated LCF, the maximum tensile stress was about twice the maximum compressive stress, thus, the tensile mean stress of about 100 MPa occurs. The hysteresis loop showed a very small amount of plastic strain. The transgranular mode and single-source fatigue characteristics were shown in the fracture surface. There were some characteristics of slip bands and cross-slip in the dislocation structures. The stress response in compressive stress-dominated LCF was opposite to that in tensile stress-dominated LCF. The fractograph exhibited mixed transgranular and intergranular modes with plastic characteristics such as dimples and multi-source fatigue characteristics. In addition to the slip bands and cross-slip characteristics, there were also some stacking faults and dislocation networks. The change in fatigue life and stress response could be explained by these microstructure features at both cases well. Based on the above two LCF damage mechanisms, energy-based life prediction model was modified. The data of LCF and creep-fatigue tests at 900 °C was used to verify the prediction accuracy of the modified life prediction model, which was found to have a good prediction accuracy.

基于拉伸应力为主的（应变比，$\mathrm{[R}={\mathrm{\epsilon }}_{\mathit{分}}/{\mathrm{\epsilon }}_{\mathit{最大限度}}=0$）和第一代定向凝固Ni基高温合金DZ445在900°C时的压应力为主（R =∞）低周疲劳（LCF），研究了拉应力和压应力对合金在高温下的破坏的影响LCF和蠕变疲劳变形。结果表明，在以拉应力为主的LCF情况下，疲劳寿命约为以压应力为主的LCF的疲劳寿命的一半。在以拉伸应力为主的LCF的情况下，最大拉伸应力约为最大压缩应力的两倍，因此，出现了大约100 MPa的拉伸平均应力。磁滞回线显示出非常小的塑性应变。断口表面显示了跨晶模式和单源疲劳特性。位错结构中存在滑带和交叉滑移的特征。以压缩应力为主的LCF中的应力响应与以拉伸应力为主的LCF中的应力响应相反。该分形仪显示出具有塑性特征如酒窝和多源疲劳特征的混合的跨晶和晶间模式。除了滑移带和交叉滑移特征外，还存在一些堆垛层错和位错网络。两种情况下的这些微观结构特征都可以很好地解释疲劳寿命和应力响应的变化。基于以上两种LCF损伤机理，对基于能量的寿命预测模型进行了修改。LCF和900°C下的蠕变疲劳测试数据用于验证修正寿命预测模型的预测准确性，