| Titanium and titanium alloys are the main structural materials of aircraft due to their comprehensive performance,and they are also the materials of choice for important components such as aero engine fans,compressor disks and blades.Due to the effects of external conditions such as temperature and load,and residual stress and roughness,titanium and titanium alloy parts are prone to fatigue failure in practical applications.At present,surface fatigue technology can improve the fatigue performance of titanium and titanium alloy.In order to meet the increasingly severe service environment,today's first task is to explore the factors that affect the fatigue performance of titanium and titanium alloys,and further improve the fatigue life of titanium alloys.In this paper,the lamellar structure TC11 titanium alloy is used as the research object.Surface strengthening is performed by two supersonic particle bombardment and laser shot peening techniques.Thereafter,the load range is 375 MPa at three temperatures of-30,25,and 150 ?.High cycle fatigue tests were performed at 550 MPa and a stress ratio of 0.1.Using scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray stress tester and other instruments to analyze the fracture morphology and crack propagation mechanism under different conditions,explore the surface nanocrystallization mechanism of titanium alloy,and provide advanced fatigue resistance for titanium alloy aviation components Manufacturing provides experimental basis and technical support.The fatigue strength of TC11 titanium alloy after bombardment by supersonic particles is improved compared to the fatigue strength of unreinforced TC11 titanium alloy.The fatigue strength decreases from 500 MPa(-30 ?)to 397 MPa(150 ?)with increasing temperature.After fatigue,the fatigue sources of TC11 titanium alloy are formed in the subsurface area of the titanium alloy.The width of the fatigue glow lines increases from 0.6 ?m(-30 ?)to 0.8 ?m(150 ?)with increasing temperature.It decreases with the increase of the surface depth,and does not change after decreasing to the hardness of the substrate.The surface residual compressive stress of the strengthened unfatigue TC11 titanium alloy is 196 MPa.After fatigue failure,the residual compressive stress of the TC11 titanium alloy has a certain degree of relaxation.The surface residual compressive stress near the fracture is 99 MPa(-30 ?),125 MPa(25 ?)and 175 MPa(150 ?).After strengthening fatigue,the surface structure of the TC11 titanium alloy undergoes severe plastic deformation.The grains in the plastic deformation zone can be refined to the nanometer level,which reduces the crack propagation rate and improves the fatigue life of the TC11 titanium alloy.When conducting high-cycle fatigue tests under different temperature conditions,the microstructure evolution mechanism of TC11 titanium alloy is different.A large number of micro-cracks and tiny holes were generated on the surface structure of the TC11 titanium alloy that failed fatigue after laser peening.The fatigue sources were formed in the near-surface area of the titanium alloy,resulting in a significant reduction in the fatigue life of the TC11 titanium alloy after strengthening,but after strengthening Compared with the unreinforced TC11 titanium alloy,the fatigue width of TC11 titanium alloy is significantly reduced.The change trend of microhardness of TC11 titanium alloy after laser peening strengthened fatigue is the same as that of TC11 titanium alloy after fatigue strengthened by supersonic particle bombardment.The residual compressive stress value of the strengthened unfatigue TC11 titanium alloy is 267 MPa,and the surface residual compressive stress value near the fracture of the TC11 titanium alloy after reinforced fatigue is 164 MPa(25 ?)and 256 MPa(150 ?),respectively.After laser peening strengthens fatigue,the surface structure of TC11 titanium alloy also undergoes severe plastic deformation,and the surface grain structure is also refined to the nanometer level. |
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