In this work, the effect of microstructure features on the high-cycle fatigue behavior of Ti-7Mo-3Nb-3Cr-3Al (Ti-7333) alloy is investigated. Fatigue tests were carried out at room temperature in lab air atmosphere using a sinusoidal wave at a frequency of 120 Hz and a stress ratio of 0.1. Results show that the fatigue strength is closely related to the microstructure features, especially the α_p percentage. The Ti-7333 alloy with a lower α_p percentage exhibits a higher scatter in fatigue data. The bimodal fatigue behavior and the duality of the S-N curve are reported in the Ti-7333 alloy with relatively lower α_p percentage. Crack initiation region shows the compound α_p/β facets. Faceted α_p particles show crystallographic orientation and morphology dependence characteristics. Crack-initiation was accompanied by faceting process across elongated α_p particles or multiple adjacent α_p particles. These particles generally oriented for basal slip result in near basal facets. Fatigue crack can also initiate at elongated α_p particle well oriented for prismatic <a> slip. The β facet is in close correspondence to {110} or {112} plane with high Schmid factor. Based on the fracture observation and FIB-CS analysis, three classes of fatigue-critical microstructural configurations are deduced. A phenomenological model for the formation of α_p facet in the bimodal microstructure is proposed. This work provides an insight into the fatigue damage process of the α precipitate strengthened metastable β titanium alloys.

在这项工作中，研究了微观结构特征对Ti-7Mo-3Nb-3Cr-3Al（Ti-7333）合金的高周疲劳行为的影响。疲劳试验是在室温下在实验室空气中使用正弦波以120 Hz的频率和0.1的应力比进行的。结果表明，该疲劳强度是密切相关的微结构特征，尤其是α _p百分比。在Ti-7333合金具有较低α _p百分比表现出疲劳数据更高的散射。双峰疲劳行为和SN曲线的对偶列于相对较低α在Ti-7333合金_p百分比。裂纹起始区示出了化合物α _p /β面。刻面α _p颗粒表现出晶体学取向和形态依赖性特征。裂缝启动伴随着横跨细长的α刻面过程_p颗粒或多个相邻的α _p颗粒。这些通常定向为基底滑移的颗粒导致接近基底的小平面。疲劳裂纹也可以发起在细长α _p阱定向为棱形滑<A>粒子。β面与具有较高Schmid因子的{110}或{112}平面非常接近。基于断裂观察和FIB-CS分析，推导出三类疲劳关键的微观结构。为α的形成的唯象模型_p提出了双峰微结构中的刻面。这项工作提供了对α沉淀强化的亚稳β钛合金的疲劳损伤过程的见解。