Study On The Surface Topography Control And Performance Of Ta2 Pure Titanium Treated By Laser Shock Imprinting

The irregular morphology induced by laser shock peening(LSP)to metal surface is prone to weak the fatigue resistance of material,therefore this paper proposed a new technology of laser shock imprinting(LSI)based on controlling the surface morphology.This technology applied a metal contact foil with high micro-hardness,low thickness and micro-texture between the absorbing layer and the sample surface in LSP.The metal foil contacted with sample surface through the mechanical effect of laser shock wave.Under the guidance of micro-texture,extruding and embossing phenomenon happened on the special zone of sample surface corresponding to the grooves of contact foil,causing micro-embossment forming on sample surface.The irregular surface morphology induced by overlapping mode of laser shock wave was converted into the features of special micro-morphology under the guidance of contact foil,which made the overall morphology of sample surface tend to be flattened and controlled.In this paper,TA2 pure titanium was used to study the surface dynamic deformation law and performance change of material treated by LSI at the combination of simulation and experiment.The main results are listed below:(1)The dynamic deformation process of TA2 pure titanium treated by LSI was simulated and the effect of technology parameters was explored.It was found that the micro-embossment zone of material surface went through five stages,static,growth,rebound,fluctuation and stabilization.With the increase of loading peak pressure from shock wave,the contact pressure between the contact foil and sample increased,which led to the higher micro-embossment appearing on the sample surface.When loading pressure rose to 4 GPa,a significant difference of residual stress appeared between the zones with micro-embossment and without micro-embossment.The height of microembossment was increased with the increase of shock wave loading time,but more serious sinking and vague difference of residual stress between the zones with microembossment happened on sample surface,making space distribution of microembossment nonuniform.(2)The effect of LSI technology parameters to surface morphology of TA2 pure titanium was researched.It was found that laser shock wave induced imprinting effect into the micro-embossment zone and flattening effect into the zone without microembossment.5 J laser shock wave energy could induce imprinting morphology with uniform space distribution,while low energy led to the low micro-embossment and high energy caused the surface profile to tilt.The increase of LSI impact time could reduce the roughness of sample surface,make the space distribution of microembossment uniform and sample surface flat.When shock time exceeded 3 times,more flaws and lower micro-embossment appeared on the sample surface.With the increases of laser energy and LSI impact time,the micro-hardness and compressive residual stress on material surface also increased,where the micro-hardness on the microembossment zone was higher than that on the zone without micro-embossment.(3)The surface control effect of LSI based on the technology improvement of LSP was explored,and fatigue experiment was used to test the vibration fatigue performance of samples.It was found that compared with 5 J-LSPed sample,the surface roughness of 5 J-LSIed sample was decreased by 47% with more flatter surface profile and controllable micro-morphology,but whose surface micro-hardness(202.7 HV)and compressive residual stress value(-298 MPa)of surface were lower.Under the test of vibration fatigue,compared with the 5 J-LSPed sample,the total fatigue life of 5 JLSIed sample was 23% higher with smaller surface crack in each fatigue stage and deeper crack initiation.Therefore,the control of LSI to sample surface morphology had a key positive effect on the vibration fatigue process of sample.