Microstructure Evolution and Tribological Property of WC Reinforced Nickel Based Alloy Surfacing Layer Fabricated at Different Preheating Temperature
Components in severe environment often fail to work due to abrasion,corrosion and fractures,surface strengthening technology has important applications in the fields of aerospace,steel and metallurgy.Nickel-WC is an ideal coating material for improving both wear resistance and corrosion resistance of components surfaces.However,WC bottom-concentrated situation generally occurs owning to large density of WC particles(16.5 g/cm3),which can cause stress concentration and increase the risk of cracking.WC bottom-concentrated situation is not desired in the fabricated process.In this study,WC particles reinforced Nickel alloy layers were prepared with different preheating schedule on 42CrMo steel substrate by powder plasma arc welding technology.The work aims to demonstrate the microstructure evolution of hard particle reinforced Nickel based alloy surfacing layers at different preheating temperature(200℃and 400℃)and investigate the effects on the mechanical and tribology properties.DML-V03BD was used to deposit the target surfacing layers.The 42CrMo steel was used as the substrate,which was cleaned with alcohol.Ni40A powder and 45%(mass fraction)WC particles added in Ni40A powder were used as the materials of bonding layer and hard layer,respectively.Before the deposition experiments,the substrate was executed at different preheating schedules of 200℃/30 min and 400℃/6 h.The bonding layer was deposited on the substrate firstly and the hard layer was deposited on the bonding layer then.The welding current used for bonding layer and hard layer was(140±10)A.The pendulum width was 20 mm.30%overlap rate between two single layers was executed.After the whole welding procedure,the samples were cooled to ambient temperature naturally.The phase composition was analyzed by X-ray diffractometer(XRD),the microstructure of the surface and cross-section of the samples was observed by scanning electron microscopy equipped with energy dispersive spectrometer(EDS)after standard metallographic etching procedures.The Rockwell hardness on the surface of the hard layer was executed at a load of 1 500 N for loading time of 5 s and the microhardness was executed with a microhardness tester on the cross-sectional of the samples with a load of 10 N for loading time of 10 s.The friction experiment was carried out by MS-T300 wear tester at a load of 20 N,rotation speed of 300 r/min,rotation radius of 5 mm and experiment time of 60 min,and the grinding ball was Si3N4 of ϕ6 mm.An electronic balance with an accuracy of 0.1 mg was used for weighing the mass loss and Alpha-step meter was used to measure the worn trace.The surfacing layer is mainly composed of γ-Ni/Fe,WC,W2C,M7C3,M23C6,Ni2W4C and Cr3C2.Surfacing layer at 200℃precipitates little secondary carbides,and WC bottom-concentrated situation is serious.Surfacing layer at 400℃precipitates massive secondary carbides,WC bottom-concentrated situation becomes weakened and homogeneity of microstructure is improved.Higher preheating temperature and longer preheating time can promote the interfacial reaction of WC particles,drive the precipitation of large secondary carbides,reduce average density of residual WC particles,effectively alleviate WC bottom-concentrated situation,improve the uniformity of WC particle distribution in the solidification microstructure,and ultimately improve the hardness and wear resistance of the surfacing layer significantly.The wear mass loss and volume wear rate of surfacing layer at 400℃preheating temperature is reduced by up to 51.85%and 51.89%compared with those of the layer at 200℃preheating temperature,respectively.The abrasive wear mechanism is more obvious with the increase of preheating temperature.
preheating temperaturePTAWNickel based WC layermicrostructurewear mechanisms
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