研究了具有双态组织的 Ti-6Al-4V-0.55Fe(TC4F) 合金在室温下低周疲劳及保载疲劳的组织特征和断裂机制，分析了合金在总应变幅为 Δε t /2=1.20% ，保载时间为 0.05 、 10 、 20 和 30 s 的低周疲劳循环应力 - 应变响应行为，并研究了疲劳变形后合金的组织演变。 发现相邻晶粒的晶体学取向差对 TC4F 合金疲劳裂纹萌生有重要影响。 一方面，无 论 是 α/α 相界还是 α/β 相界，晶界两侧晶粒的晶体学取向差越大，越易萌生裂纹；另一方面， α 相内产生的孪晶导致孪晶界相邻晶粒较大的取向差，从而也可在 α 相内部萌生裂纹。 随着疲劳保载时间的增加，导致 α 相中更多的柱面滑移系激活，位错滑移使相界面产生应力集中，进而使得疲劳寿命降低。 最后讨论了不同保载时间下的疲劳裂纹扩展方式。

The microstructure characteristics and fracture mechanisms of Ti-6Al-4V-0.55Fe(TC4F) alloy with bimodal structure under low cycle fatigue and dwell fatigue at room temperature were investigated in this paper. The stress-strain behavior of the alloy was analysed for low cycle fatigue with a total strain amplitude of Δε t /2=1.20% and dwell time of 0.05, 10, 20 and 30 s, and the microstructure evolution of the alloy after fatigue deformation was also investigated. The results show that the difference in the crystallographic orientation of adjacent grains has an important effect on fatigue crack initiation in the TC4F alloy. On the one hand, whether at the α/α phase boundary or the α/β phase boundary, the greater the difference in grain orientation, the more likely it is that cracks will initiate; on the other hand, twinning within the α phase leads to a greater difference in orientation between the adjacent grains of the twinning boundary, which can lead to the formation of cracks within the α phase. As the fatigue dwell time increases, it leads to the activation of more prismatic slip systems in the α phase and the dislocation slip causes stress concentration at the phase boundary, which in turn leads to a reduction in fatigue life. Finally, the fatigue crack propagation mode is discussed for different dwell time.