Effect Of Laser Shock On Surface Integrity And Friction Performance Of Thin Plate

304 stainless steel has good oxidation resistance and mechanical properties,so it is widely used in industrial production.However,its further application and development are limited by its disadvantages such as low hardness and easy surface wear.In this paper,the surface modification of 304 stainless steel sheet was carried out by laser shock processing（LSP）technology,and the residual stress field on the surface of the 304 stainless steel sheet after single and double sided laser shock processing treatment was investigated by numerical simulation and experiment.The influence of LSP treatment on the surface integrity and friction properties of the sheet were analyzed,which can provide a reference for the industrial application of LSP treated 304 stainless steel.Firstly,the residual stress field under different LSP parameters was simulated by ABAUQS.The results show that the maximum residual compressive stress of the plate first increases and then decreases after increasing the peak pressure of the shock wave.The residual stress hole（RSH）is easy to occur in the central area of the laser spot after LSP treatment,and it is more obvious when the peak pressure is large.With the increase of spot diameter,the maximum residual compressive stress value of the plate increases and the depth of the affected layer is deeper,and the RSH phenomenon in the central area of the spot weakens.With the increase of spot overlap rate,the uneven distribution of residual stresses on the surface of strengthened region gradually decreases.The change of LSP path has little effect on the profile of stress distribution,but mainly affects the local stress size and distribution.The influence of spot overlap rate on the surface integrity of 304 stainless steel sheet during LSP treatment was experimentally studied.The experiments show that the depth of the pit changes more uniformly,the surface height difference decreases,and the contour changes more uniformly with the increase of the spot overlap ratio.The residual stresses and microhardness on the sample surface are increased by laser shock.When the spot overlap rate is 50%,the residual stress on the surface of the impact area fluctuates around-190 MPa,and the experimental and simulation results are relatively consistent.Meanwhile,the microhardness of the sample surface increases from 210 HV in the unstrengthened state to 243 HV.A large number of lamellar twins were produced on the surface microstructure of LSP treated samples,and the high density deformation twins produced greatly improved the surface properties of the sample.The RSH phenomenon on the surface of 304 stainless steel sheet subjected to two sided laser shock processing（TSLSP）treatment was researched by numerical simulation and experiment.The investigations show that the RSH phenomenon is mainly caused by the convergence of surface unloaded stress wave emitted from the boundary of laser spot.When the size of treated plate is small,the effect of surface stress wave reflected by the plate boundary cannot be neglected.Under the action of TSLSP,the RSH easily occurs on the surface of the related thick-sectional sample.As the spot diameter increases,the peak of RSH does not change significantly,but the width becomes wider.The spatial pressures distribution of shock wave affects the RSH phenomenon.With the enhance of the applied pressure of shock wave,the RSH phenomenon becomes more obvious.Finally,the effect of LSP treatment on the friction and wear properties of 304stainless steel sheet under different working conditions was investigated.The results show that when AL₂O₃ball is used,there is no obvious difference between the wear amount and the 3D morphology of the wear scar of the strengthened sample and the unstrengthened sample.When the load was 10 N,the wear mechanism of the sample did not change significantly.When the load is 30 N,the wear mechanism of the unstrengthened sample is fatigue wear,abrasive wear and adhesive wear,while the strengthened samples are mainly abrasive wear,accompanied by adhesive wear.When 304 stainless steel ball is used,the wear loss of the LSPed sample decreases obviously,and the average friction coefficient and the height difference of the worn surface are less than those of the unstrengthened sample.When the load is 10 N,the wear mechanisms of the samples are both abrasive wear and adhesive wear.When the load increases to 30 N,a large amount of delamination occurs on the surface of the unstrengthened sample.The friction and wear properties of the LSP treated sample are improved,and the surface delamination phenomenon is weakened.