Study On Microstructures And Properties Of In-situ Grown WC Hard Phase Reinforced Nickel-based Coating By Laser Cladding

Laser cladding technology can obtain a cladding layer with good metallurgical bonding with the substrate and excellent performance.In-situ growth of hard phase can effectively solve the problem of uneven distribution of reinforcements directly doped with hard particles.In this paper,45#steel commonly used in ball valve of mine hydraulic support was adopted as the matrix material,WO3,B4C,Al and Ni60 powder were used to prepare laser clading and in-situ grown WC hard phase reinforced nickel-based cladding layers.The feasibility of in-situ grown WC reinforced phase prepared by(WO3+B4C+Al)mixed powder system was evaluated by thermodynamic calculation.The effects of different laser cladding parameters,powder particle size,hard phase content and CeO2/Yf2O3 rare earth doping on the microstructure,phase composition,friction and wear and electrochemical properties of in-situ grown WC hard phase reinforced nickel-based cladding layer were analyzed.The conclusions are as follows:(1)At 100-4500 K,the in-situ growth reactions of WC,W2C,WB,W2B and W2B5 phases are spontaneous and exothermic.Meanwhile,the driving force of W2C phase formation is greater than that of WC phase.In addition,the thermodynamic calculation results can only be a necessary condition rather than a sufficient condition for the spontaneous in-situ reaction.(2)When the laser power is 3000 W and the scanning rate is 3 mm/s,the microstructure of the cladding layer is dense,no obvious defects such as cracks and pores are found in the cross-section structure,the WC particle size is moderate,the distribution is uniform,and the metallurgical combination with the substrate is good.At this time,the phases of the cladding layer are γ-(NiFe)solid solution,Al2O3,W2C,WC,WC3,WC1-x,WB2,WB4 and Cr23C6 phases.The light gray phase in the microstructures of the cladding layer is the matrix phase γ-(NiFe)solid solution,dark gray phase is the polymerization phase of Cr23C6 and other intermetallic compounds,and white massive particle phase is WC hard phase.Meanwhile,under the condition of low heat input,a large number of butterfly shaped structural precipitates will appear in the cladding layer.Under appropriate heat input,the WC particles in the cladding layer are massive and evenly distributed in the cladding layer.When the heat input is too large,the massive WC particles in the cladding layer will dissolve and decarburize,forming flake secondary precipitates around the WC particles.The butterfly structure formed by the refinement and enrichment of WC particles has a positive effect on the hardness of the cladding layer,but the improvement of wear and corrosion resistance of the cladding layer is not as good as that of massive WC particles.(3)When the particle size of B4C powder is W5 and the content of doped(WO3+B4C+Al)mixed powder is 25%,compared with 45#steel substrate,the hardness,wear resistance of dry friction and wet friction in emulsion environment,and corrosion resistance of the cladding layer grown in situ are significantly improved,and the hardness is increased by 3-5 times.The dry friction and wear mechanism of the cladding layer is mainly the adhesive and abrasive wear caused by the falling off of WC hard particles,while the friction coefficient and wear amount of friction and wear in the emulsion environment are small,which does not cause obvious damage to the cladding layer.(4)When the content of doped rare earth oxide CeO2 is 0.75%and the content of Y2O3 is 1.50%,the performance of the cladding layer is best.The CeO2 phase and stable rare earth compounds CeNi5 and Ce3Ni6Si2 phases generated by the reaction appear in the phase of the cladding layer doped with CeO2.The Y2O3 phase and stable rare earth compounds Ni17Y3,YAl3 and AlNiY phases appear in the phase of the cladding layer doped with Y2O3.Rare earth oxides have good grain refinement and purification effect on the cladding layer structure,which enhances the diffraction peaks of each phase.At the same time,the smaller WC particles improve the wear resistance of the cladding layer,but also make the hardness of the cladding layer slightly lower than that of the cladding layer without rare earth oxide.An appropriate amount of rare earth oxide has a positive effect on the wear and corrosion resistance of the cladding layer,but when the content of rare earth oxide is too high,the performance of the cladding layer will also be reduced.