| Piston rod is the core part connecting the piston and the working parts,and its performance directly affects the overall reliability and service life of the hydraulic system.The piston rod and the guide sleeve are in friction contact,and they are prone to wear during the continuous relative movement.Besides,the piston rod is exposed to the corrosion medium in the service environment,which causes electrochemical corrosion.Using surface modification technology to improve the surface hardness,wear resistance and corrosion resistance of piston rod is of great significance,which reduces the surface damage and maintain the stable operation of hydraulic system.In this paper,to solve the problem of wear and corrosion in the service process,the ceramic reinforced composite cladding layer was prepared on the surface of 45 steel.The main cladding materials systems divided into 3 categories:Ni60A+ZrC,Ni60A+Zr70Ni30+G and Ni60A+Zr70Ni30+B4C.ZrC was in-situ generated in Ni60A+Zr70Ni30+G and Ni60A+Zr70Ni30+B4C cladding coatings.The influence of laser power,scanning speed and powder ratio on the phase constituent,microstructure,microhardness,wear resistance and corrosion resistance were studied.The microstructure formation mechanism was analyzed.The Ni60A+ZrC cladding layer was mainly composed of γ-(Fe,Ni),ZrC,Cr2C,FeNi,Cr23C6 and Cr3C2.The ZrC morphology was dendrite,block,or quadrangle particles.The hardness of the cladding increased with the increase of the ZrC addition.The average microhardness ofNi60A+50wt.%ZrC cladding layer was 573.62±82.36 HV0.2,which was about 2.49 times that of the substrate.The friction coefficient of the cladding layer was about 0.43～0.46.Ni60A+40wt.%ZrC cladding layer had the best wear resistance,and the wear volume was 1.83%of the substrate.Among the cladding layers with different ZrC addition,Ni60A+30wt.%ZrC cladding layer had the highest diffusion coefficient n and RCT,as well as the best corrosion resistance.The corrosion current density icorr was only 4.31%of the substrate,and Rp was 18.03 times that of the substrate.The corrosion morphology of the cladding layer was characterized by selective corrosion.The main phases of the Ni60A+(Zr70Ni30+G)cladding layer included γ-(Fe,Ni),ZrC,(Fe1.5Ni1.5)B,Cr2B,NiB and Fe3B.The microstructure of the cladding layer was mainly composed of γ-(Fe,Ni),interdendritic eutectic and ZrC.With the ZrC addition of 70wt.%,large agglomerated ZrC appeared in the cladding layer.With 70wt.%(Zr70Ni30+G)addition,the best wear resistance was obtained,and the wear volume was only 5.24%that of the substrate.With 60wt.%(Zr70Ni30+G)addition,the highest corrosion resistance was obtained.The icorr was only 5.98%of the substrate,and Rp was 12.31 times that of the substrate.The main corrosion mechanism of the cladding layer was selective corrosion.Ni60A+(Zr70Ni30+B4C)cladding layers mainly consisted of α-(Fe,Ni),ZrC,Fe2B and Cr3C2.The microstructure of the cladding layer was mainly composed of α-(Fe,Ni)dendrite,α-(Fe,Ni)+Fe2B eutectic,and fine ZrC particles.With the(Zr70Ni30+B4C)addition of 70wt.%,the wear resistance of the cladding layer was the highest,and the wear volume was only 0.86%of the substrate.With the increase of the(Zr70Ni30+BB4C)addition,the diffusion coefficient n decreased gradually,and the corrosion resistance of the cladding layer decreased.With 50wt.%(Zr70Ni30+B4C)addition,the icorr was only 8.24%of the substrate,and the Rp was 6.46 times that of the substrate.The corrosion surface showed the selective corrosion characteristics.The phase of α-(Fe,Ni)in dendrite and eutectic were preferentially dissolved,leaving the bare ZrC particles and Fe2B.By preparing metal ceramic composite layers on the surface of 45 steel substrate,the influence of process parameters and powder ratio on the microstructure,wear and corrosion resistance are studied.The wear and corrosion mechanism of the cladding layer are analysed,which provides some theoretical and experiment reference for the application of laser cladding in the surface modification of piston rod. |
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