Dwell sensitivity of titanium alloys at ambient temperature (∼25 °C) is a well-reported phenomenon, although the question about the phenomena of crack initiation remains open. In this work, the normal and dwell fatigue response of a near alpha titanium alloy is studied. A dwell fatigue debit (number of continuous cycles to failure to number of cycles to failure with a dwell period) of up to 2 and 10 were observed at two different load levels. Analysis using scanning electron microscopy, electron back scattered diffraction and transmission electron microscope-based orientation imaging microscopy (TEM-OIM) revealed that the formation of microcracks at very early stages of dwell fatigue loading was the major reason for this decreased life. The initiation of these cracks was observed to be a strong function of the local crystallography of the constituent grains. A modified pile up model in which the shear stress on the pile up plane is calculated using stress redistribution at the grain level is used to explain the micromechanisms of crack nucleation in dwell fatigue. The elastic and plastic anisotropy of the hexagonal crystal, the microtextural characteristics and strong stress redistributions at the grain level results in the nucleation and propagation of these microcracks.

钛合金在环境温度（~25 °C）下的停留敏感性是一个被广泛报道的现象，尽管关于裂纹萌生现象的问题仍然悬而未决。在这项工作中，研究了近 α 钛合金的正常疲劳响应和驻留疲劳响应。在两个不同的负载水平下观察到高达 2 和 10 的驻留疲劳借记（连续失效循环数与驻留期失效循环数）。使用扫描电子显微镜、电子背散射衍射和基于透射电子显微镜的定向成像显微镜 (TEM-OIM) 进行的分析表明，微裂纹的形成在保压的早期阶段，疲劳载荷是寿命缩短的主要原因。观察到这些裂纹的萌生是组成晶粒的局部结晶学的强大功能。一种改进的堆积模型，其中堆积平面上的剪应力使用晶粒水平的应力重新分布进行计算，用于解释驻留疲劳中裂纹形核的微观机制。六方晶体的弹性和塑性各向异性、微结构特征和晶粒级的强应力再分布导致这些微裂纹的成核和扩展。