| Oil pumping polished rod is the key equipment which used widely in the course of rod pumping. The erosion and corrosion failure caused by the mechanical wear and erosion corrosion is familiar to the oil pumping polished rod, which limits the development of the rod pumping technology.Based on the oil pumping polished rod common material 20CrMo steel, the paper chose the cobalt-base, nickel-base and iron-base self-fusible alloy as laser cladding coating materials.Laser melting experiments were carried out on the crosscurrent CO2 laser device(HGL9450-000,5kW), and the laser coatings of densified structure and non-macroscopic defects were attained by the synchronistic laser sending powder mode.By means of OM,SEM,XRD etc,the phase constitution and microstructure of different coatings were observed and analyzed. With the disc-pin tribological wear equipment,the tribologieal wear experiments were carried out on the surface of 20CrMo and three kinds of self-fluxing alloy-coated specimen, and the tribological wear mechanism was also discussed. Besides, the corrosion electrochemistry behavior of different cladding layers were tested by Gamry PCI4/750 electrochemistry workstation.The study found that the laser cladding parameters had great impact on the microstructure,macro-configuration and the capability of the cladding layers. The cladding coatings with excellent surface quality, fine microstucture,lowdilution,high micro-hardness and outstanding metallurgical combination interface with substrate were obtained under the cladding parameters of P=3.2kw,Vs=9mm/s,D=5mm.Cladding layers possessed the characteristics of rapid solidification.With the differences of G/R in the process of solidification, the microstructure and morphologies in different parts of the cladding layer varied. Convective motion in the bath promoted the inclusion of alloy elements and inpelled full mixture of alloying elements and the liquid in the bath, which had a significant effect on the quality of laser surface cladding coating.Phase analysis results showed that cobalt alloy coating phase composed mainly by theγ-Co phase and (Cr, W)7C3 phase. Ni-based alloy coating phase composed ofγ-(Ni, Cr, Fe) phase, Cr23C6, FeNi3 and Ni2.9Cr0.7Fe0.36 phase and Fe-based alloy phase wasγ-Fe, FeNi3,Cr2Fe6.37Mo0.1Ni1.3Si0.3 and C0.09Fe1.91 phase.The average hardness value ofСo-based , Ni-based and Fe-based alloy coating was 520HV0.2, 408HV0.2,and 370HV0.2 respectively.The hardness value of 20CrMo alloy substrate is 270HV0.2. Moreover, the hardness of the specimen is significantly increased compared with the substrate after laser cladding.In the wear experiment,the results indicated that the friction coefficient decreased with the load increases, and the increase degree of the substrate is faster than that of the one having laser cladding coating.The rubbing wear performance of laser cladding layer had a significant increase compared with the substrate.The corrosion test testified that thelaser cladding layer had a stronger resistance ability to pitting corrosion and alkaline etching, which compared with the substrate 20CrMo alloy steel. The self-corrosion current of cladding layer was up to three order of magnitude smaller than 20CrMo alloy.The corrosion resistance of laser cladding layer enhanced markedly than the substrate. |
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