Microstructure And Mechanical Properties Of WC/Co Composite Coatings By Laser Cladding

In recent years,45 steel has been widely used in various important structural parts with stringent service conditions.As a result,the failure of structural parts caused by surface wear and corrosion of 45 steel always occurs frequently,resulting in low working efficiency and high production cost.Therefore,surface treatment must be carried out to obtain excellent surface properties.The cladding layers were prepared on the carbon steel using WC strengthened Co-based alloy as deposited materials by multi-track laser cladding.The deposited materials included Nano-structured WC and Co-based alloy(VC+Cr₃C₂,Cr₃C₂,VC).The samples exhibited a good metallurgical bonding between the clad layer and the substrate.Compared with the substrate,all the cladding layers have an improved friction and wear resistance and a better oxidation resistance with the increased time(0-50h)at 800°C.The mutual reaction of Cr₃C₂ and VC is helpful to an improve wear resistance,which is superior to that of the cladding layers with additives VC or Cr₃C₂.However,Cr₃C₂ has a more oxidation resistance performance than VC.The constitution and phases of cladding layers concluded hcp-?and bcc-?cobalt and hard carbides such as Co Cx,V₈C₇(N1 and N3),Cr₃C₂(N1 and N2),and a small of decarburization in the form of Co₃W₃C and WC_1-x.It is found that obvious elemental inter-diffusion between the different phases indicated by the results of transmission electron microscopy(TEM)and electron backscatter diffraction(EBSD).The average grain size of hard carbides is 1.69,0.36 and 1.61?m in sample N1,N2,and N3.In contrast,the average grain size of Co binder is 1.07,1.04,and 1.09?m(original grain size is 1?m).Under the effect of laser heat source,the carbides grew rapidly through interfacial diffusion and boundary migration mechanism.The coalescence played a important role on the grain growth,which followed Kirkendall effect and Ostwald coarsening mechanism.