Effects of laser shock peening on microstructure and mechanical properties of TC17 titanium alloy

Owning to the foreign object damage (FOD), a TC17 titanium alloy blade in aero-engine is prone to be fractured. So the fatigue strength needs to be improved. Plates of TC17 titanium alloy were treated by laser shock peening (LSP) with different laser fluence. Microstructure, microhardness and residual stress of TC17 titanium alloy treated by LSP with different laser fluence were examined by X-ray diffraction (XRD), transmission electron microscope (TEM), sclerometer and residual stress tester. 4 GW/cm² was chosen with better reinforcement effect and vibration fatigue tests of TC17 titanium alloy blades were conducted to verify the feasibility of LSP for this kind of blade. The results show that a great deal of high-density dislocations and nanocrystals are generated in the material surface layer. And the greater the laser power fluence is, the smaller the refined grains are. The microhardness and residual stress value decrease with the depth. The hardness affected depth is about 800 μm, and a residual stress, -200 MPa, still exists in 500 μm depth. The hardness is highest, 4310 MPa, with the greatest compressive residual stress, 628.2 MPa, in the surface when the laser fluency is 4 GW/cm², and there is a good thermal stability at 280 and 450℃. The vibration fatigue life of the TC17 titanium alloy blade treated by LSP in 4 GW/cm² has improved by 200%.