The ultra-high cycle fatigue performance of TC4 titanium alloy specimens under different laser power densities was carried out by an ultrasonic fatigue testing machine. The fatigue fracture mechanism was analyzed by scanning electron microscope (SEM), and the reliability of ultra-high cycle fatigue life was analyzed. The results show that the specimen fatigue performance is obviously improved after laser shock peening, and the fatigue fracture surface shows a transgranular quasi-cleavage cracking mode with facets on the surface or subsurface, corresponding to high cycle fatigue and ultra-high cycle fatigue, respectively. At the same time, the position of the crack origin zone shifts sideways. The ultra-high cycle fatigue life obeys both lognormal distribution and three-parameter Weibull distribution, and the influence of reliability and confidence on reliability life depends on the sensitivity of unilateral tolerance confidence factor to both. According to the p-γ-S-N fitting curves, it was concluded that the fatigue life is higher and the scatter is smaller under the power density of 3.42 GW/cm2, so it is the best impact parameter.
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