Preparation And Properties Of Ni+WC+h-BN Composite Cladding Layer On Carbon Steel

Nickel-based alloy powder self-melting slag performance is good,and can form a good metallurgical combination with the substrate.As a result,it is rapidly promoted and applied.In addition,nickel-based self-melting alloys have good wettability on Ti C,WC,Ti B and other hard ceramic particles.The strength and wear resistance of a single alloy can be improved by adding WC.However,the formed coating was difficult to meet its requirements under extreme working conditions.It is necessary to further extend the multi-component composite coating.That is,we tried to add WC hard phase and h-BN to the nickel-based alloy,so that it can ensure the strength of the composite coating while owed better wear resistance and corrosion resistance.Therefore,in this paper,the composite cladding layer of Ni+WC+h-BN was prepared on the surface of 45#steel by vacuum cladding technology.The microstructure and formation process of its cladding layer were studied,and the wear resistance and corrosion resistance of the composite cladding layer with different h-BN content were also studied.Experimental results show that:In this paper,the WC-h-BN/Ni-based composite cladding layer was prepared on the 45 steel by vacuum cladding technology.From the cladding layer surface to the substrate,it was divided into surface area,composite area,transition area,diffusion fusion zone,and diffusion impact zone.And its main phase includesγ-Ni solid solution,Fe Ni₃,Cr₇C₃,Cr₂₃C₆,WC,W₂C,Ni₃Si,Ni₃B,Cr B,Cr₂B,BN and Ni_2.9Cr_0.7Fe_0.36.From the perspective of the entire cladding layer,the interdivision of elements occurred in the interface area,forming a fusion belt of 16μm thickness.The composite region has a variety of forms of phase structure.Due to the influence of the powder particles themselves and temperature,a needle-like phase composed of compounds such as Cr₇C₃and Cr₂₃C₆appears in the surface region.By compared the microstructure of the cladding layer with different h-BN content.It can be seen that the compactness of the cladding layer decreases with the increase of the content,and combined with its performance requirements.The 0.6%h-BN cladding tissue is relatively reasonable.With the temperature increases,the sintered neck grows in the cladding layer,makes the pores gradually change from a closed spheroidized state to contraction and extinction,and then the composite cladding layer with dense structure is formed.The polarization test of electrochemical corrosion was carried in 3.5%NaCl solution.It can be seen that the corrosion resistance of the composite cladding layer formed is gradually improving after the addition of WC and WC+h-BN in the nickel-based alloy.With the increase of h-BN content from 0 to 0.8wt%,the self-corrosion potential value of Ni+WC+h-BN composite cladding layer increases first and then decreases,and the self-corrosion current density decreases first and then increases.The corrosion resistance of the Ni+WC+h-BN composite cladding layer reduced by an order of magnitude compared with45steel.The results demonstrated that the corrosion resistance of the composite cladding layer will not be generally enhanced with the increase of h-BN.With the progress of the corrosion process,the corrosion resistance of the Ni-based alloy cladding layer to resist Cl^-gradually decreases.By adding WC hard phase and h-BN,the occurrence of galvanic corrosion in the cladding layer was slowed down to a certain extent.And the diffusion path of chloride ions becomes tortuous,thereby reducing the corrosion rate of the cladding layer.The Ni+WC+0.6%h-BN composite cladding layer has the most positive self-corrosion potential and the smallest self-corrosion current density.That is,this cladding layer has the best corrosion resistance.The wear resistance of the cladding layer has a great change after adding h-BN to the Ni+WC composite cladding layer.With the increase of h-BN content,the friction coefficient and wear rate of the cladding layer show the first increase,then decrease,and finally increase again.By observing the microscopic morphology of the worn surface of the cladding layer,it is known that with the increase of h-BN content,the h-BN participating in the friction process also continues to increase.The h-BN and the stable oxide film generated during the friction process jointly play a role in reducing friction,which improves the wear resistance of the cladding layer.When the content of h-BN was too large,the structure of the cladding layer was relatively loose,resulting in a large area of wear and spalling.The exposed area containing h-BN was oxidized to form an oxide film during friction,which cannot meet the wear consumption,so it is difficult to exert its anti-friction protection effect,so that the cladding layer shows poor wear resistance.The roughness of the worn surface of the abrasive piece corresponds to the surface wear resistance of the cladding layer.Comprehensive analysis shows that when the addition amount of h-BN is about 0.6wt.%,the friction coefficient and wear rate of the cladding layer are the smallest,and the friction reduction effect was the best,so the wear resistance of the corresponding cladding layer was also the best.