In this paper, the small fatigue crack behavior in titanium alloy TC4 under different stress levels was investigated. Single-edge-notch tension specimens were axially fatigued with stress ratio of 0.1 at room temperature. Results show that the naturally initiated cracks nucleate from the α/β interfaces. When the crack is below a critical length of ∼200 µm, crack growth rates exhibit large fluctuations and temporary retardations due to microstructure effects. But once the crack length exceeds ∼200 µm, the fluctuations in crack growth rates die down and the crack grows more rapidly. There is no distinct effect of stress level on small crack growth rate. A linear relationship exists between the total fatigue life and crack initiation life.
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