Corrosion And Wear Coupling Behavior And Mechanism Of High-speed Laser Cladding Stainless Steel Coating

In the oil and gas equipment industry,the sucker rod coupling is the key part to connect the sucker rod,and eccentric wear damage during oil production is a common form of failure.As oilfield exploitation enters the later stage,the water content in the production fluid of oil wells is increasing,and the corrosion to sucker rods and couplings becomes more and more serious,resulting in frequent occurrence of corrosion and wear failure accidents of sucker rod couplings.Therefore,the use of advanced surface engineering technology to prepare a coating with excellent performance on the surface of the sucker rod coupling to improve its ability to resist corrosion and wear has attracted increasing attention from researchers.In this paper,high-speed laser cladding technology is used to cladding stainless steel coating on the surface of medium-carbon quenched and tempered steel.X-ray diffractometer（XRD）and optical microscope（OM）were used to analyze the cross-sectional structure of the coating,the friction and wear tester was used to measure the wear performance of the coating,and the wear morphology of the coating was observed by SEM to analyze the wear resistance and wear mechanism.The electrochemical workstation was used to measure the potential polarization curve and electrochemical impedance spectroscopy of the coating,and analyze its corrosion resistance and corrosion mechanism.The electrochemical corrosion friction and wear tester was used to test the corrosion and wear coupling behavior of the coating in 3.5wt.%Na Cl solution.The experimental results show that the surface of the high-speed laser cladding stainless steel coating is smooth,the roughness of the coating decreases after the remelting treatment,and the brightness increases.After flaw detection,no cracks are found,and the quality of the cladding coating is good.The coating was analyzed by XRD as a martensite phase structure.The structure of the coating shows typical directional solidification characteristics,and the bonding surface of the coating and the substrate forms a bright white flat crystal band,which is metallurgically bonded.The coating is flat crystal,cellular crystal,columnar crystal and equiaxed crystal from bottom to top.The microstructure of the remelted coating is smaller,more uniform and denser than that of the cladding coating,multiple lap marks disappear,fewer defects,and greatly reduced segregation.The hardness of the coating gradually increases from the surface layer,and the average hardness is about 525HV_0.1,which is about 2.5 times that of the substrate.The coefficient of friction of the coating is larger than that of the substrate,and the remelted coating has the highest friction reducing performance.The wear resistance is just the opposite.The relative wear resistance of the remelted coating is the best,followed by the cladding coating,and the relative wear resistance of the substrate is the worst.It can be seen from the wear morphology that the wear mechanism of the coating is mainly adhesive wear and brittle peeling,while the matrix is mainly abrasive wear.The electrochemical test results show that the self-corrosion potential of the coating is significantly higher than that of the substrate,the corrosion current density is significantly reduced,and the charge transfer resistance is also far higher than that of the substrate.The corrosion resistance of the coating is greatly improved compared with that of the substrate.It is that the remelted coating has obvious passivation in the scanning potential range set in the experiment.The composition of the cladding coating is the same as that of the remelted coating.Due to the difference in structure,the corrosion resistance of the remelted coating is better.The corrosion-wear coupling test results show that the open circuit potential of the coating and the substrate show a downward trend when friction is loaded in 3.5wt%Na Cl,and the open circuit potential decreases more obviously as the load and sliding frequency increase.Due to the strengthening of corrosion,the friction coefficient gradually decreases.Under external load,the self-corrosion potential of the coating and the substrate shifts negatively,and the current density increases.The greater the load,the more obvious the damage effect,which is reflected in the increase in the degree of negative shift of the polarization curve.The passivation film on the coating surface becomes incomplete,pitting corrosion is more likely to occur,and the formation of the passivation film becomes more difficult.In the total loss of corrosion and wear,the synergistic effect of the matrix and the cladding coating accounts for about one-third,and the remelted coating can account for about half.The remelted coating is easier to passivate,and friction removes part of the passivation film,resulting in leakage of fresh metal,intensified corrosion,and more likely to be affected by the synergistic effect of corrosion and wear.The absolute value of pure corrosion is very small,but the promotion of wear in the synergistic effect of corrosion and wear is extremely serious.Abrasion accelerates the corrosion of the material surface,and the corrosive action greatly accelerates the abrasion,and the two together lead to the loss of the material.