Decoupling Multi‐scale Fatigue Damage Evolution in Titanium Alloys: The Role of Residual Stress Fields

ABSTRACT This study investigates fatigue damage evolution in TC17 titanium alloy under residual stress using acoustic emission (AE), scanning and transmission electron microscopy. The compressive residual stress sample U1 exhibits approximately 19% longer fatigue life than stress‐free U1R. Fractography shows U1R is dominated by tearing ridges and secondary cracks, whereas U1 features slip steps and intersecting slip planes. During crack propagation in segments A (A1/2) and B (B1/2), U1 displays ~50% shorter average secondary crack length and ~40–51% lower crack density than U1R, indicating that compressive residual stress critically regulates dislocation activities—multiplication, sliding, and activation. In U1R, multiplication and activation occur concurrently with activation dominant; in U1, sliding predominates followed by activation due to reduced stress intensity at crack tips. Dislocations accumulate at grain boundaries and activate under cyclic loading. Based on variations in dislocation activities, configurations, and AE signals at crack stages, this study proposes an integrated AE‐microdamage characterization method.