| Summary: | Gradient crystalline structure in surface layer of TC11 titanium alloy was obtained through ultrasonic impacting and rolling process. Microstructure, work hardening state, residual stress distribution, and surface roughness in modified layer were measured and analyzed to get a comprehensive knowledge of surface characteristics. The effect of gradient crystalline surface layer on fatigue behavior was then investigated. High-cycle fatigue test results show that a considerable improvement of almost 19.3% with respect to untreated fatigue samples under the cycles of 5 × 106 was obtained. Obvious difference in fatigue crack source region can be found between original samples and treated series. Crack sources of all the original ones were found in surface or near-surface areas, while crack sources of all the treated ones distinctly located at near central positions. To explain this phenomenon, an in-depth discussion on the mechanism of fatigue improvement through ultrasonic impacting and rolling was performed. Keywords: Titanium, Impacting, Rolling, Fatigue, Gradient crystalline structure
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