Oxygen-enriched layer enhancing fatigue performance of a near-α titanium alloy

Although thermal exposure is a commonly used engineering process to enhance the properties of titanium alloys by diffusing oxygen onto the surface, the mechanism by which it affects fatigue performance is not fully understood. This work systematically investigates the effect of thermal exposure on the fatigue properties of a near-α titanium alloy through a combination of fatigue testing, in-situ nanoindentation, micropillar compression experiments, and an integrated differential phase contrast (iDPC)-scanning transmission electron microscope (STEM), particularly emphasizing the inhibitory role of surface oxygen-enriched layer on fatigue crack propagation. Results show that after thermal exposure, the oxygen-enriched layer formed on the alloy’s surface relieves surface stress concentration, thus enabling the alloy to maintain high fatigue strength even after up to 10 7 fatigue cycles at 650 MPa. Interstitial oxygen atoms within the oxygen-enriched layer induce lattice distortion and promote the formation of oxygen-enriched stacking faults at fatigue crack tips. These oxygen-enriched stacking faults efficiently absorb energy required for crack propagation, deflect the crack propagation path, extend the propagation period, and alleviate stress concentration; these effects collectively enhance the fatigue resistance of the alloy. This work systematically elucidates the mechanism by which the oxygen-rich layer delays crack propagation through microstructural regulation, providing a theoretical basis for designing high-performance titanium alloys.