Study On The Frictional Wear Performance Of Laser Fusion Coated TiC-WC/Ni60 Composite Coating On The Work Surface Of Shield Hob

The shield hob is one of the core components of the shield machine and is the key to the shield machine’s ability to tunnel properly.The stability and reliability of the shield hob directly affect the speed and stability of tunneling as the shield hob is continuously rolled to push the shield along the tunnel excavation surface.The design and manufacture of shield hobs need to take into account the countermeasures under different geological conditions,as well as the balance of construction efficiency and quality.If the hob design is unreasonable or the manufacturing process is not fine,it will lead to frequent shutdown and maintenance of the shield machine during the construction process,thus reducing the construction efficiency and quality.Therefore,improving the wear resistance of shield hobs is an urgent problem in shield excavation.To address the problem of shield hobbing with bias wear and chipping leading to hob failure during tunnel boring,this paper prepared four kinds of WC-TiC/Ni60composite coatings with different content ratios of 5wt%TiC+25wt%WC,10wt%TiC+20wt%WC,15wt%TiC+15wt%WC and 20wt%TiC+10wt%WC on the work surface of shield hob using laser melting technology,and used Finite element simulation,SEM,EDS,hardness tester,and friction wear tester were used to analyze their friction wear performance,and to try to get the coating with the best wear resistance.From the ANSYS simulation results,it was found that the surface temperature change of the molten layer appeared to be fast hot and fast cold,and the best molten effect was obtained when the laser power was 1200W in a comprehensive view.The stress analysis of the pin head by ABAQUS statics shows that the stress concentration mainly occurs during the hob penetration,and the stress decreases as the hob rolls and the static friction changes to rolling friction.During the hob penetration,the stress is mainly concentrated at the tip of the hob.The simulation of rock breaking by ABAQUS shows that the laser coating of TiC-WC/Ni60on the surface of H13 steel has a small increase in the rock breaking efficiency of the hob.The macroscopic morphology of the clad layer is flat,without obvious defects and the porosity of the clad layer is calculated to be below 10%,so the quality of the clad layer is good.The surface morphology of WC-TiC/Ni60 coating with different WC and TiC contents in four groups was observed under SEM,and it was found that the surface of the melt layer was smooth and of good quality.The microstructure was observed by metallurgical microscope from bottom to top as coarse dendritic crystals,columnar crystals and fine cellular crystals.The TiC-WC/Ni60 clad coating mainly contains TiWC₂,Cr₄Ni₅W and Cr₃C₂hard phases.By hardness test,the average hardness of 5wt%TiC+25wt%WC coating is the lowest801.2 HV,which is 1.21 times that of the substrate,except for the substrate.When the TiC content reaches 20wt%,the average hardness of the molten layer is the highest,which is 1.46times that of the substrate.The cross-sectional microhardness of the clad layer showed a trend of decreasing,then increasing and finally decreasing,and the highest hardness of the clad layer appeared at the subsurface of the clad layer.The maximum average friction coefficient was 0.3521 for 15wt%TiC coating and the lowest friction coefficient was 0.3364 for 10wt%TiC coating;The wear of the molten coating is significantly lower than that of the matrix.The minimum wear of the 15wt%TiC coating is1.311 mm³,which is 86.7%lower than that of the matrix;The wear of the matrix is mainly abrasive wear and adhesive wear,while the wear of the coating is mainly by embrittlement spalling,abrasive wear and oxidation wear.Compared with the substrate,the self-corrosion current of the clad layer is significantly reduced and the corrosion resistance is significantly improved.WC-TiC/Ni60 coating can effectively reduce the equivalent force on the surface of the material and reduce the wear of the hob surface caused by the large impact load.At the same time,it can reduce the contact stress on the hob surface and reduce the material removal caused by the impact.