激光冲击强化对TC17钛合金微观组织和力学性能的影响

Effects of Laser Shock Peening on Microstructure and Mechanical Propertiesof TC17 Titanium Alloy

针对航空发动机TC17钛合金叶片易受外来物打伤实际问题,需要进一步提高叶片的疲劳强度。对板状TC17钛合金进行不同激光功率密度下的激光冲击,分别利用X射线衍射仪、透射电子显微镜、残余应力测试仪和显微硬度计分别对激光冲击前后TC17钛合金的组织和力学性能进行了观察和测试,再选取强化效果较好的功率密度为4 GW/cm2时对叶片强化后进行振动疲劳试验。结果表明:TC17钛合金在不同功率密度激光冲击后,表面组织产生大量高密度位错和纳米晶,随着功率密度的增大,晶粒细化程度越大;残余应力值和显微硬度都随深度增加而减小,表面显微硬度提高了20%,并形成800μm左右的硬度影响层;而功率密度为4 GW/cm2时提高幅度最大,HV0.1硬度为4310 MPa,表面残余压应力达到628.2 MPa,且残余应力在280和450℃下具有较好的热稳定性;TC17钛合金叶片在4 GW/cm2参数下强化后,其振动疲劳寿命提高了2倍。

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 TC 17 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 500μm 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%.