Research And Application Of Plasma Surface Modification For Subway Shield Machine Cutter

With high electron temperature,high power density,high energy density,and completing high speed quenching,sputtering and ion implantation in one step,the pulsed high energy density plasma(PHEDP)technique can greatly improve the surface hardness,wear and corrosion resistance of the substrate.Owing to high energy utilization ratio,high productivity,relatively low use-cost,the plasma cladding technique has attracted more and more attention.The coating produced by plasma cladding technique has fine and homogeneous microstructure typical rapid solidification feature.The plasma clad coating is usually metallurgically bonded to the substrate, which make the coating can bear severe impact load.The underground stratum layer of Beijing district is mainly composed of soft soil and gravels.The shield cutter subjected to sever wear.The service life of the shield cutter is relatively short during work process.Facing to this situation,in this paper,the PHEDP and plasma cladding techniques are utilized to produce protective film on the surface of the shield cutter to improve the wear and corrosion resistance and prolong the service life of the cutter.Ta(C)N ternary film was deposited by PHEDP on stainless steel.The film's microstructure,surface topography,nanometer hardness,and distribution of element along depth were analyzed,and tribology behaviors were also tested.The results showed that the Ta(C)N film had a high hardness(14GPa)and high modulus(250GPa); between the film and substrate,there was a wide transition layer,which made the film a finn combination with the substrate;the Ta(C)N film had an excellent tribological properties under dry sliding friction test at room temperature.A wear resistance and corrosion resistance(Cr,Fe)₇C₃/γ-Fe composite coating was fabricated on surface of 0.45%C carbon steel by plasma cladding.The microstructure of the coating was analyzed,and the microhardness,tribological properties and corrosion resistance properties were also tested.The results showed that the average microhardness of the(Cr,Fe)₇C₃/γ-Fe composite coating was 820HV;the relative wear resistance was 35 times higher compared to 0.45%C carbon steel;the coating had an excellent corrosion resistance.According to optimized parameters,the Ta(C)N ternary film was deposited on the carbide bit of shield cutter by PHEDP.According to optimized parameters and the powders ratio,wear resistant and corrosion resistant(Cr,Fe)₇C₃/γ-Fe composite coating were fabricated on the towards soil surface of the cutter body by plasma cladding.After the two kinds of plasma surface modification treated the shield cutters were tested on fabricating yard of Beijing subway No.10 line,the results showed that the cutter's wear resistance and corrosion resistance were greatly improved,and service cycle was extended obviously.