Microstructure and Tribocorrosion Properties of Cr-W-Mo-V Coating Fabricated via Laser Hot-wire Cladding
Owing to the development of marine oil and gas resources,drilling and exploitation equipment are affected by coupled damage from corrosion and wear.The development of wear-and corrosion-resistant coating materials as well as preparation technologies guarantees the safe and reliable operation of marine equipment.Laser cladding is a promising surface modification technology that is widely used in machine-component repair and functional coatings.However,the limitations of the deposition and material-utilization rates of the conventional laser cladding technology restrict its widespread use.Laser hot-wire cladding(LHWC)is a promising,efficient,and energy-saving coating-deposition process.In this study,Cr-W-Mo-V steel coating is prepared on the surface of a 20 steel substrate using LHWC technology.The microstructure and phase composition of the coating are analyzed using a ZEISS optical microscope,an XRD-7000 X-ray diffractometer,and a JSM-7200F scanning electron microscope.The microhardness of the coating is measured using an HV-100A microhardness tester.The dry friction factor,polarization curve,and electrochemical impedance of the coating are measured using a reciprocating electrochemical corrosion friction and wear tester(MFT-EC4000,HUAHUI).The loss of wear marks is measured using three-dimensional morphometry,and the microscopic morphology and elemental distribution of the wear marks are observed using scanning electron microscopy and energy dispersive spectroscopy.The open potential,dynamic polarization curve,and constant-potential polarization curve of the coating at various friction load in 3.5 wt.％NaCl solution are analyzed and the tribocorrosion mechanism is discussed.The prepared Cr-W-Mo-V steel coating is uniform and compact-without cracks,pores,or other defects-and is primarily composed of carbide,martensite,and residual austenite phases.The microstructures are primarily columnar and cellular crystals.The average hardness of the cladding layer is 780 HV0.1,which is approximately 6.5 times the hardness of the substrate.The friction factor of the coating is between 0.15 and 0.18,and the friction factor and wear amount of the coating are smaller than those of the substrate.The wear volume of the coating increases from 2.36 × 10-3 to 1.33 × 10-2 mm3 as the friction load increases;meanwhile,the wear mechanism changes from abrasive wear to abrasive wear,and from adhesive wear and oxidation wear.The free-corrosion potential of the cladding coating is-0.386 V and the free-corrosion current density is 3.45 × 10-6 A/cm2,both of which are higher than those of the substrate.Additionally,the impedance arc radius of the coating is much larger than that of the substrate,thus indicating that the coating possesses excellent corrosion resistance compared with the substrate.In the 3.5 wt.％NaCl solution,as the friction load increases,the open-circuit potential of the coating decreases from-0.22 to-0.35 V,the friction factor decreases from 0.2 to approximately 0.13,the corrosion potential of the coating decreases from-0.4 to-0.45 V,and the corrosion current density increases slightly,thus indicating that the friction significantly promotes corrosion.As the applied potential increases,the corrosion current density of the cladding layer increases and the friction factor decreases,thus indicating that corrosion clearly promotes wear.A synergistic effect is indicated between corrosion and wear.In conclusion,Cr-W-Mo-V steel coating with a compact structure,a uniform microstructure,and excellent tribocorrosion performance is successfully prepared via hot-wire laser cladding.It can be used for the surface modification of components used in oil and gas drilling as well as in exploitation equipment used in harsh tribocorrosion environments.
laser hot wire claddingCr-W-Mo-V steel coatingmicrostructuretribocorrosion
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