| In order to improve the wear resistance and corrosion resistance of 45#steel,laser cladding technology was used to prepare Ni35+11%WC and Ni35+11%WC+20%Cr coatings on its surface,and X-ray diffractometer（XRD）and gold Phase microscope（OM）,scanning electron microscope（SEM）,micro Vickers hardness tester,ring block friction and wear tester and electrochemical corrosion workstation have systematically studied the morphology,composition,structure and wear corrosion of the cladding layer Performance,the influence of the addition of alloying element Cr on the structure and performance of the coating is analyzed.The main research results are as follows:1)Microstructure and performance of laser cladding Ni35+11%WC coatingThe section of Ni35+11%WC coating has no defects such as pores and cracks,and the metallurgical bond between the coating and the substrate is good.The main components of the coating areγ-Ni,Cr7C3,Ni3B,Ni2Fe and W2C.The metallographic phase of the coating is composed of columnar crystals and equiaxed crystals.Compared with the substrate,the Ni35+11%WC coating has improved abrasion resistance and hardness,and the hardness value of the coating reaches about 710HV;the morphology of the coating after wear shows furrow and adhesive wear.According to the comparison of electrochemical corrosion data,the electrochemical corrosion resistance voltage of45#steel is-1.057V,and the corrosion resistance current is 1.750A/m2;the corrosion potential of Ni35+11%WC coating is-0.833V and the corrosion current is 0.981A/m2.In the polarization curve,the passivation zone of the coating has a long time,while the passivation zone of 45#steel has a shorter duration.In the impedance test,the capacitive reactance radius and phase angle of Ni35+11%WC coating are larger than those of 45#steel;further study the equivalent fitting circuit data of the coating,Ni35+11%WC coating The charge transfer resistance and Rf value are also greater than the corresponding value of 45#steel.It shows that Ni35+11%WC coating has better corrosion resistance than 45#steel.2)Microstructure and properties of laser cladding Ni35+11%WC+Cr coatingThe Ni35+11%WC+Cr coating has uniform structure,smooth cross-section,no pores and unmelted particles,and the coating forms a good metallurgical bond with the substrate.After phase test,the coating is mainly composed of Cr23C6,Cr B,r-Ni,Cr7C3,Ni3B,Ni3Fe,Fe3Cand W2C phases.The coating is dominated by small equiaxed crystals and a small amount of small columnar crystals,affected by the temperature gradient,the core crystals of the coating are coarse.The average hardness value of the coating is about 600HV,and the coating hardness value fluctuates greatly.In the polarization curve test,compared with Ni35+11%WC coating,the self-corrosion voltage of Ni35+11%WC+Cr coating is-0.475v,the corrosion current is 0.481A/m2,and the tafel line of the coating is positive To offset.Through the electrochemical impedance spectroscopy test,compared with the Ni35+11%WC coating,the Ni35+11%WC+Cr coating has a larger capacitive reactance radius and a higher phase angle.In the equivalent fitting circuit,compared with Ni35+11%WC coating,the charge transfer resistance of Ni35+11%WC+Cr coating is 689.46Ω·cm2;the ion corrosion resistance Rfvalue of the coating’s passivation film It is 103.655Ω·cm2.Therefore,in the electrochemical corrosion test,the Ni35+11%WC+Cr coating can produce a good passivation film and improve the corrosion resistance of the coating.3)The influence of Cr addition on coating structure and performanceIn terms of the coating structure,the addition of Cr reduces the pores and cracks of the Ni35+11%WC+Cr coating.After comparison,the Cr-added coating increases the Cr23C6hard phase.At the same time,the Cr element has the effect of refining the grains,and the equiaxed and columnar crystals of Ni35+11%WC+Cr become finer.The content of Cr has a certain effect on the dilution rate of the coating.When it reaches 30%Cr to50%Cr,the dilution rate of the coating tends to stabilize.In terms of the performance of the coating,the addition of Cr reduces the hardness and wear resistance of the coating.The reason is that Cr element and C element form too much Cr23C6,Cr7C3hard phase,which causes the coating to appear grain boundary embrittlement,and the hardness and wear resistance are slightly weakened.In the 3.5%Na Cl solution electrolysis experiment,the Tafel curve of the coating after adding Cr has a large positive shift,and the absolute value of the self-corrosion voltage and the number of corrosion currents show a decreasing law;at the same time,in the impedance spectrum test,after adding Cr The coating will also increase the impedance value.In the fitted equivalent circuit,the transfer resistance value of the coating after adding Cr and the resistance value of the ionized corrosion resistance of the passivation film will also increase.Therefore,it can be concluded that the addition of Cr makes the coating form a good passivation film,reduces the number of corrosion cells on the coating surface,reduces the electrode potential difference,and improves the electrochemical corrosion resistance of the Ni35+11%WC+Cr coating. |
PDF Full Text Request