Vibration Fatigue Life And Fracture Analysis Of TC6 Titanium Alloy Treated By Laser Peening

Laser peening(LP)is a technology that uses high power pulsed laser to irradiate the surface of a workpiece to induce a shock wave pressure that exceeds the dynamic yield strength of the material.LP causes severe plastic deformation and induces grain refinement and high density dislocations which can significantly improve the stress distribution and microstructure of the surface of materials.Therefore,LP can effectively restrain the initiation and propagation of the cracks in materials and significantly improve the service life of components.In this dissertation,TC6 titanium alloy was treated by LP with different laser power density and peening times to explore the effects of laser parameters on the surface integrity and fatigue life of the material.The vibration fatigue fractures were analyzed by fracture mechanics and fatigue improvement mechanism of LP was investigated by fracture morphology in different stages of vibration fatigue failure.The main contents of this paper are as follows:The producing and estimating model of compressive residual stress induced by LP were investigated.Combining vibration fatigue failure and fatigue fracture theory,the improvement mechanism of fatigue crack propagation rate induced by LP was studied on the aspects of the fatigue limit,crack propagation threshold and stress intensity factor,respectively.A high power Nd:YAG laser was used in LP experiments of TC6 titanium alloy samples.The residual stress and microhardness in the LPed samples were measured.The laser confocal microscopy,scanning electron microscopy and transmission electron microscopy were used to study the microstructure of LPed specimens,including ?/ ? phase morphology,grain size,dislocation morphology,etc.The vibration fatigue life of TC6 titanium alloy specimens strengthened by LP was measured by the vibration fatigue testing system.The effects of laser power density and peening times on the vibration fatigue life were studied.Moreover,the vibration fatiguefractures of TC6 titanium alloy were investigated by the scanning electron microscope.The effects of LP on the vibration fatigue fractures of TC6 titanium alloy were analyzed in the crack source,crack propagation and final fracture zone,respectively.The fatigue crack propagation rate of TC6 titanium alloy were investigated by fatigue striation spacing.