Effect of different shot peening intensities on fatigue resistance of TC17 titanium alloy

In order to improve the fatigue resistance of the TC17 titanium alloy，shot peening on the surface was carried out.The effects of different shot peening intensities on fatigue resistance of TC17 titanium alloy were studied by means of rotary bending fatigue test，fracture analysis，residual stress field analysis，microstructure observation and surface integrity analysis before and after shot peening.The results showed that surface roughness of titanium alloy was increased from 0.315 μm to 0.5-1.0 μm after shot peening.Severe plastic deformation occurred on the surface during shot peening and the surface grains were refined.Residual compressive stress was introduced into the surface，the layer depth of residual compressive stress was about 125-151 μm，and the maximum compressive stress appeared about 30 μm in depth from the surface.The fatigue life of the rotary bending sample after 0.3 $\mathrm{m}\mathrm{m}?\mathrm{N}$ shot peening was better than that of other samples.Under the stress levels of 740 MPa and 840 MPa，the fatigue life of 0.3 $\mathrm{m}\mathrm{m}?\mathrm{N}$ shot peened sample increased by 4.5 times and 7.5 times than that of non-shot peened sample，respectively.The increase of fatigue life was attributed to the inhibition of fatigue crack initiation and propagation by the refined grains，high-density dislocations and residual compressive stress on the surface induced by shot peening.Excessive shot peening intensity caused the high surface roughness，delamination and microcrack formation on the surface，which resulted in the decrease of fatigue life of 0.35 $\mathrm{m}\mathrm{m}?\mathrm{N}$ and 0.4 $\mathrm{m}\mathrm{m}?\mathrm{N}$ shot peened samples.