Preparing Of WC/316L Gradient Composite Coating By Steady Magnetic Field Assisted Laser Melt Injection

Due to composite,structure and performance with spatial gradient distribution,gradient composite materials have some special properties which conventional materials do not have.In this paper,the WC/316 L metal-matrix gradient coating was prepared by laser melt injection with a steady magnetic field.In the metal-matrix gradient coating WC showed different distribution with the change of the magnetic field intensity.Based on preliminary experiments,superior process parameters were chosen to perform laser melt injection experiments with different magnetic flux density.The influence of magnetic flux density on the gradient composites was investigated by comparing the composite layers under different magnetic flux.The principles of steady magnetic field through controlling the flow of molten pool to assisted laser melt injection making gradient composite coating was revealed.The distribution of WC particles and the change of microstructure were analyzed by optical microscope,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).The micro-hardness,wear resistance and corrosion resistance of the coating were tested by micro-hardness tester,friction and wear tester and electrochemical workstation as well.The results show that steady magnetic field can suppress the flow of the molten pool and reduce the drag force of particles.The distribution of WC particles is mainly affected by change of molten pool flow.With the increase of steady magnetic flux density,the trend of WC particles distribution on surface of composite coating increases.The steady magnetic field does not change the phases' type of composite coating surface,but the W phase increases significantly,the size of eutectic structure becomes larger and the quantity of eutectic increases.In the upper and middle of composite coating,the hardness increases with the magnetic flux density increasing when the intensity of steady magnetic field strength is lower than 0.8 T.However,the hardness decreases with the magnetic flux density increasing when the intensity of steady magnetic field is higher than 0.8 T.In the bottom of the composite coating,the hardness decreases more rapidly with the magnetic field strength increasing when the steady magnetic field strength is in the range of 0-1.6 T.The friction and wear tests show that 316 L substrate is mainly damaged by the adhesive wear while composite coating is mainly due to the abrasive wear.The higher magnetic flux density is,the more of WC particles in the upper part of LMI layer become and the better wear resistance is.The composite coating corrosion resistance is better that of the substrate.However,the steady magnetic field has limit effect on corrosion resistance of composite coating.