激光熔覆原位生成NbC对CoCrFeNiMo0.5高熵合金/TiC复合涂层微观组织及耐磨性能的影响OA

Laser cladding technology is an advanced surface modification technology,which can improve the surface properties,such as hardness,wear resistance and corrosion resistance,without changing the substrate properties.Metal carbide ceramic phase has outstanding wear and corrosion resistance and high hardness,and is an ideal coating reinforcement phase.However,due to the different parameters and poor compatibility between the substrate and the additive phase,the coating has low bonding strength and obvious defects such as hot cracking.In this work,CoCrFeNiMo0.5 high entropy alloy/TiC composite coating was prepared on Q235 substrate by indirect synthesis method of in-situ synthesis of ceramic phase by laser cladding technology.Nb elements with different proportions(x=0,2.5wt.%,5wt.%,7.5wt.%and 10wt.%respectively)were added,and the powder was mixed evenly and preset on the clean Q235 steel surface.With XL-F2000 W fiber laser processing system,under the the power of 1 300 W,the laser spot diameter of 2.5 mm,the overlap rate of 40%,the defocus of+5 mm,and the scanning speed of 600 mm/min,multi-channel laser cladding was carried out.The sample was cut with wire cutting machine,with the cross section polished,and covered with aqua regia for corrosion.Then,the microstructure of the coating was observed by scanning electron microscope(SEM,Zeiss,Germany,ZEISS Sigma),and the EDS(EDS Spectroscopy:Oxford 30 Xplore)spectrum of each selected surface was collected by energy spectrometer to analyze the composition.The phase composition of the coating was analyzed by X-ray diffractometer(XRD,SmartLab 9 kW,Rigaku,Tokyo,JPN),the microhardness of the coating and substrate was tested by microhardness technology(MHVD-1000AT,China),the wear resistance of the coating was tested by friction and wear machine(SFT-2M,China),the wear amount of the coating was calculated,and the morphology after rubbing the surface was observed.A well-formed CoCrFeNiMo0.5 high entropy alloy/TiC-NbC composite coating was prepared on Q235 surface by laser cladding technology,and the mechanical properties of the coating reached the best value when x=7.5.With the addition of Nb,the hysteresis diffusion effect of high entropy alloy led to the absence of in-situ phase NbC in the coating,and the coating formed an irregular crystal structure,and the properties of the coating were mainly affected by TiC.When the mass fraction of Nb was 10wt.%,the enhanced phase of NbC was generated in-situ in the laser molten pool.The alloying of Nb changed the phase composition and morphology of the composite coating.From the surface to the interface,the crystal structure of the coating evolved from cotton wool-like crystals to columnar crystals and cell crystals,and finally turned into uniform and refined cells.The average hardness of the coating reached 615.8HV.The results of friction and wear showed that the wear depth of S4 coating was 25 μm,the friction coefficient and wear rate were 0.589 and 0.15×10-5 mm3/(N·m),respectively,and the wear resistance was obviously improved.This work provides a new idea for the study of in-situ formation of strong carbon compounds such as NbC by laser cladding,and offers a powerful reference for the study of in-situ synthesis.