Microstructure And Properties Of WC Composite Coatings By Laser Melt Injection Assisting With A Steady Magnetic Field

Laser melt injection(LMI)is a kind of effective technology to achieve the metal matrix coating.In this paper,WC particles were injected into the surface of 316 L stainless steel by LMI process with a steady magnetic field,the influence of the steady magnetic field on the microstructure and properties of strengthened coating were studied.Different processing parameters such as laser beam power,scanning velocity and powder feed rate will affect the quality of coating.The microstructure and phase composition of the coating were analyzed by means of optical microscope(OM),scanning electron microscopy(SEM),X-Ray diffraction(XRD)and energy dispersive spectrometer(EDS).The cross-section microhardness of LMI coating was measured by Vickers hardness tester,and the abrasion performance of the LMI coating was characterized through the friction coefficient.The results show that the steady magnetic field can suppress the flow of the molten pool,the distribution of WC particles will also be affected.WC particles mainly distribute on surface of LMI coating when steady magnetic flux density is 1.4 T.The phases of the LMI coatings are mainly composed of γ(Fe-Ni)solid solution,WC,W2 C and M6C(Fe3W3C,Fe4W2C).A lot of fishbone-like eutectics are observed in coating without steady magnetic field assisting.While the microstructure of upper area of the coating with steady magnetic field assisting is uniform,there is only very small eutectic structure.The lower area of the molten pool has no WC particles,and the microstructure is mainly γ phase dendrite.The results of overlapping coating experiments performed by LMI assisting with steady magnetic field show that the overlapping area contains more particles than that of other areas’,the microstructure of the overlapping area is different from that of the non-overlapping area.The property of the LMI coating were analyzed.It was found that the microhardness of the LMI coating without steady magnetic field is higher than that of the coating with steady magnetic field assisting.When the strength of steady magnetic field is 1.4 T,the wear resistance of the LMI coating surface is obviously improved,and the coefficient is 0.7,which is lower than that of coating without steady magnetic field.The surface of the coating without steady magnetic field is deep and the WC particles are crushed seriously.There is no obvious wear on the coating surface which assisted by steady magnetic field,and only a small amount of WC is broken.