| Surface treatment technology has become one of the key technologies to improve the surface performance of components because of its high efficiency and low cost.Common surface treatment technologies in industry include electroplating,thermal spraying,physical / chemical vapor deposition,etc.The principle of these techniques is to form a metal layer on the material surface,and then to make up the defects of the hardness,wear resistance and corrosion resistance of the matrix,in order to improve the comprehensive performance of metal parts.However,with the higher requirements for the load,speed and temperature that the mechanical parts can bear,single surface treatment method can not satisfy the real requirements.So it is urgent to develop new technology that can further improve the surface performance of metal parts.In this paper,the surface of Q235 sample was treated by laser shock strengthening and surface coating.The feasibility of composite treatment process was evaluated by hardness and surface roughness test,surface morphology characterization,and friction-wear test.The specific research contents are as follows:(1)The transmission characteristics of shock wave through the homogeneous medium and multi-layer medium were analyzed,and the transmission process of shock wave in homogeneous medium(Q235)and multilayer medium(Cr-Q235)was simulated by ABAQUS numerical simulation.The residual stress distribution in the surface and depth directions was studied and the effect of shock wave enhancement was characterized as follows: for homogeneous medium,the residual stress of the surface after impact is compressive and the overlapping rate of the spot has great influence on the distribution of residual stress.For the multi-layer medium,the residual tensile stress of the surface after impact is larger,which has a negative effect on the impact strengthening effect.Compared with multi-layer medium,the depth of shock wave in homogeneous medium is deeper.The research in this part is helpful for choosing the parameters for laser shock experiment and provide theoretical support for subsequent experimental results analysis.(2)The influence of laser shock processing on the surface morphology of coatingmaterials was analyzed.Laser induced shock waves causes severe plastic deformation on the surface of materials.Compared with the original sample,the roughness of coating and impact specimens is increased to varying degrees.Laser induced shock wave produces tensile stress at the interface,and tensile stress induces micro cracks in the brittle film.The hardness of the sample surface can be improved by the grain refinement by laser shock strengthening,but the micro crack will increase with higher laser energy,and the micro crack has a negative effect on the hardness test.Therefore,grain refinement and microcrack are two main factors affecting surface hardness.(3)The effect of laser shock processing on the friction and wear properties of coating materials was analyzed.It is found that surface roughness and hardness are the key factors affecting the wear resistance of the samples.The results show that the wear resistance of the technique,shocking firstly and then coating,is better than that of its counterpart technique,coating firstly and then shock,under our experimental conditions.Conducting coating firstly and then laser shock processing,causes micro-cracks in the coating,which greatly reduce the wear resistance of the sample surface.The sample surface roughnesses are significantly increased due to the non-optimized laser shock processing and the coating.These parameters of laser shock processing and coating process are optimized to reduce the surface roughness of the sample,wich is beneficial to improve the applicability of the combined treatment process under dry friction condition.. |
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