Laser shock peening induced fatigue crack retardation in Ti-17 titanium alloy

Laser shock peening is an advanced surface treatment technique of great interest introducing beneficial compressive residual stress and further enhancing fatigue crack propagation resistance of metallic components. In this study, fatigue crack propagation and subsequent retardation of Ti-17 titanium alloy under laser shock peening are presented. Varying degrees of fatigue crack retardation were observed after peening with pulse energy of 20 J and 30 J. The fatigue life was increased up to 2.4 times that of the unpeened counterpart. The fatigue arrests were observed in the deceleration zone after peening, showing different angles with the fatigue crack path as the peening energy varied. The fatigue crack retardation mechanism based on the plastic zone size and crack propagation energy density drop at the crack tip was further discussed, and a crack tip energy density criterion was proposed to quantitatively understand the fatigue crack retardation.