Effect of Shot Peening on the Long Life Fatigue Properties of Ti6Al4V with Different Heat Treatment

In order to investigate the effect of shot peening on the long life fatigue properties of Ti6Al4V (TC4), ultrasonic fatigue tests were performed with a frequency of 20 kHz. According to different heat treatment, two groups of specimens were surface modified by shot peening with an Almen intensity of 0.10 mmA~ 0.15 mmA and an overlapping rate of 100%. One group was stress-relief annealed at 650 °C, and the other was then treated with solution-aging. With the shot peening, both the depth of the residual stress layer and the maximum compressive residual stress are increased. Surface hardness is also increased. The fatigue strength is increased, but enhancement is no more than 5% because of the increase of surface roughness. Noticeably, all of the TC4 specimens after shot peening show inner crack initiations. Oxide inclusion is always the core of cracks, and the small crack propagation in crack initiation area acts as the slip of α-phase.