| Cryogenic laser peening(CLP)is a surface deformation strengthening technology under the coupling condition of ultra-high strain rate and ultra-low temperature,which can improve the surface layer microstructure and surface mechanical properties,thereby suppressing the initiation and propagation of cracks,eventually increasing the fatigue life.In this paper,TC6 titanium alloy was taken as the research object,theoretical research,numerical simulation and experimental analysis methods were used to study the effects of CLP treatment on microstructure,typical structural vibration mode,and surface properties of TC6 titanium alloy.The fatigue life extension mechanism of CLP on TC6 titanium alloy was explored.The main contents are as follows:(1)The plastic deformation mechanism under the coupling condition of cryogenic temperature and ultra-high strain rate was studied.Based on the analysis of the microstructure of the sample characterized by transmission electron microscopy(TEM),the microstructure evolution of TC6 titanium alloy at different cryogenic laser peening stages was obtained.The surface compressive residual stress of the samples was detected by XRD method,and the stability of the residual stress under vibration load was discussed.The formation and release mechanism of the surface compressive residual stress of the material under cryogenic laser peening were revealed.(2)The nano-indentation tester was used to measure the nano-hardness and elastic modulus of different treated samples,and the strengthening mechanism of cryogenic laser peening on the nano-hardness and elastic modulus of TC6 titanium alloy was explored.The ABAQUS finite element analysis software was used to simulate the modal of the vibrating specimen under different processing methods,the first to fourth order vibration mode and natural frequencies were obtained.The vibration modal test system was used to measure the damping ratio and natural frequency of the vibration sample.The gain mechanism of metal damping and natural frequency of cryogenic laser peening were analyzed from the perspective of twin structure and dislocation structure.(3)Based on fatigue and fracture theory,the fracture characteristics and influence factors of different vibration fatigue stages were analyzed.The vibration fatigue test was carried out,and the fatigue life of vibration samples under different treatments was measured;Scanning electron microscope(SEM)was used to observe the fracture morphologies of the samples under different treatment methods,and the microscopic characteristics of different fracture areas were obtained.On this basis,the extension mechanism for vibration fatigue life of cryogenic laser peening was comprehensively revealed from the perspective of microstructure,vibration characteristics and residual stress. |
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