Formation Mechanism And Properties Of Ni-WC-GO Composite Cladding Layer On Cast Steel Surface

The composite material formed by adding different ceramic particles and self-lubricating materials in the metal-based alloy powder has good resistance to various forms of wear and corrosion,which is mainly combined with the advantages of hard particles and strong matrix.Nickel-based composites with WC reinforced particles are widely used in mechanical equipment parts with severe wear and corrosion conditions to improve equipment life,such as mining equipment,abrasive tools and instrumentation.Within this work WC and graphene oxide(GO)reinforced Ni-based coating which were fabricated on ZG45 substract through vacuum cladding technoiogy.The microstructure and phase composition of the microstructure and the formation mechanism of the coating were studied,and the corrosion wear properties of the composite coatings with different compositions were tested.The results showed that:Ni-based composite coatings with different compositions were prepared by vacuum cladding on the surface of ZG45.The microstructure was uniform and uniform,and an effective metallurgical bond was formed with the matrix.The coating cross section is mainly a 4 mm thick composite layer(CZ),a 1 mm thick transition layer(TZ),a 20 um thick diffusion fusing zone(FZ),and a 250 um thick diffusion affected zone(DZ).The composite region is composed of a nickel-based solid solution,a hard phase(Cr₇C₃,Cr₂₃C₆,W₂C,C),a eutectic phase(Ni₃Fe,Ni₃Si,Ni₃B),a complex hexagonal lattice structure M₇C₃(M=Ni,Cr,W)and a complex cubic lattice structure M₂₃C₆(M=Cr,W,Ni)phase composition.The transition layer is composed of Cr₇C₃,Cr₂₃C₆,eutectic phase and nickel-based solid solution.The diffusion fusion zone is composed of a nickel-based solid solution close to the coating and an iron-based solid solution close to the matrix,and the diffusion-affected zone is composed of pearlite.There are three main stages in the vacuum cladding process:(a)the melting starts from the surface,and the micromelting increases with increasing temperature;(b)when the temperature reaches 1020°C,the transition layer is basically melted,and the elemental diffusion between the transition layer and the matri x increases.A new zone is formed,and the composite layer can only be partially melted;(c)the temperature reaches 1060°C and is kept for 10 min,at which time the elements diffuse in a large amount to form a diffusion fusion zone of about 20?m.The composite layer is completely melted,the hard particles are rearranged and partially dissolved,and the W-rich multiphase carbide precipitates,eventually forming a composite coating surrounded by the WC and the precipitated W-rich composite carbide surrounding the Ni particles.Ni-based alloy coatings were added with reinforcing phase WC particles and GO flakes,and the corrosion resistance of the composites was improved.The Ni+20%WC+0.8%GO composite coating has the best corrosion resistance,and its self-corrosion potential is 0.3677 V higher than the matrix ZG45.The corrosion current density of the composite coating is nearly two orders of magnitude lower than that of the substrate.This is because the WC particles have high hardness and are not easily corroded,so the corrosion resistance is very strong.A certain amount of WC can effectively improve the corrosion resistance of the composite coating.The graphene oxide sheets are encapsulated in Ni particles,WC particles and WC particles are decomposed to form The surface of the composite carbide particles forms an effective protective film,and a certain amount of GO can improve the corrosion resistance of the coating.Adding reinforcing phase WC particles and GO flakes to the Ni-based alloy coating significantly improves the wear resistance.The Ni+30%WC+0.8%GO composite coating has the best wear resistance,the average friction coefficient is 15%lower than the matrix ZG45,and the composite coating wear rate is 85%lower than the matrix ZG45.A certain amount of hard particles WC is added to the Ni-based alloy coating,and the wear resistance of the composite coating is enhanced due to its high hardness.Adding a certain amount of GO flakes,during the rubbing process,the graphene oxide flakes and the wear debris form a graphene oxide transfer film mainly composed of Ni oxide on the coating wear scar under the action of temperature and pressure.A graphene oxide transfer film mainly composed of Fe oxide is formed on the wear surface of the Gr15 steel ball of the pair of parts.The relative motion between the friction pairs can be replaced by the relative sliding between the graphene oxide transfer films,and the wear resistance of the coating is significantly improved.