激光熔覆等原子比CoCrFeNi-V高熵合金涂层的磨损行为研究OA

The work aims to develop an equiatomic high-entropy alloy(HEA)coating with excellent wear resistance.In the HEA system,CoCrFeNi-based HEAs with a face-centered cubic(FCC)structure have attracted significant attention due to their good ductility,excellent fracture toughness,high work-hardening capacity and outstanding corrosion resistance.However,their relatively low hardness and limited wear resistance have restricted their widespread application to a certain extent.By rationally adjusting the composition of HEAs,it is expected to significantly improve the wear resistance of the alloys.In this experiment,equiatomic V particles were added to CoCrFeNi HEA and CoCrFeNi coatings and CoCrFeNiV coatings were prepared by laser cladding technology.Their phase composition,microstructure,microhardness and wear resistance were studied.Q235B was used as the substrate.After removal of surface oxides and impurities with 80#sandpaper,the plates were placed in an oven to dry for subsequent use.Equiatomic CoCrFeNi HEA powder was selected and equiatomic V elements were added.The powders were mixed for 4 hours in a planetary ball mill at a rotation speed of 18 r/min.A standard mold was used to prefabricate a mixed powder with a thickness of(2±0.1)mm on the substrate surface.The laser cladding process was carried out in an Ar gas environment with a flow rate of 5 L/min.A continuous fiber processing system(XL-F2000W)was used for laser cladding.All parameters were obtained from pre-experiments(laser power:1 800 W,scanning rate:500 mm/min,defocusing amount:+5 mm,spot diameter:2.5 mm,overlap rate:50%,number of melting passes:20 and melting length:45 mm).The prepared coating was cut with a wire electrical discharge machine.A field-emission scanning electron microscope(SEM,QUANT 250,Eindhoven,USA)equipped with an energy-dispersive spectrometer(EDS,Noran System 7,Thermo Fisher Scientific,MA,USA)was used to analyze the cross-sectional microstructure and element distribution of the coating.To detect and analyze the surface phases of the coating,a high-resolution X-ray diffractometer(XRD,SmartLab 9 kW,Rigaku,Tokyo,JPN)was used,with Cu-Kα radiation(λ=0.154 059 8 nm),a diffraction angle range of 20°-90°,a voltage of 40 kV,and a current of 40 mA.The microhardness of the coating was measured with a Vickers hardness tester(model:MHVD-1000AT,manufacturer:SE,Yizong Precision Instrument Co.).A load of 200 g was applied at the same horizontal position for 10 seconds and the average of three measurements was taken as the result.Additionally,the wear resistance of the coating was evaluated with a pin-on-disc friction and wear tester(model:SFT-2M,manufacturer:Lanzhou Zhongkehua Science and Technology Development Co.,Ltd.,Lanzhou,China)equipped with a displacement sensor.The coating friction test used a 4 mm GCr15 steel ball as the counterpart under wear conditions,with a load of 25 N,a rotational radius of 2 mm,a rotational speed of 200 r/min and a test duration of 30 minutes.The morphology of the worn surface of the coating was observed through SEM.An equiatomic CoCrFeNiV HEA was designed.By comparing the microstructure,phase composition,hardness and wear resistance of CoCrFeNi and CoCrFeNiV HEA coatings,the effect mechanism of V elements on the mechanical properties of HEA coatings was explored,providing theoretical and experimental basis for improving the wear resistance of HEAs.CoCrFeNi and CoCrFeNiV HEA coatings were prepared by laser cladding technology.The phase composition of the coatings was analyzed by X-ray diffraction(XRD),the microstructure and element distribution were observed by scanning electron microscope(SEM),the microhardness of the coatings was tested by a microhardness tester and the wear resistance was evaluated on a wear tester.The wear mechanism was analyzed by combining the morphology of the worn surface.Compared with the CoCrFeNi coating,the peak position of the FCC phase in the CoCrFeNiV coating shifted to the left and a new intermetallic compound phase(Ni3V)was formed.Its grains were significantly refined,with uniform element distribution and no obvious segregation.Performance tests showed that the CoCrFeNi coating had an average hardness of 188.16HV,an average friction coefficient of 0.75 and a wear rate of 7.16×10-5 mm3/(N·m),with the main wear mechanisms being abrasive wear and oxidative wear.In contrast,the CoCrFeNiV coating had an average hardness of 222.91HV,which was 18.5%higher than that of the coating without V addition.The average friction coefficient was 0.69,a decrease of 8% and the wear rate was 1.97×10-5 mm3/(N·m),a reduction of 72.5%.Its wear mechanisms were mainly oxidative wear,adhesive wear and abrasive wear.The oxide lubricating layer formed on the coating surface effectively reduced the friction coefficient.The addition of V promoted the formation of the Ni3V intermetallic compound phase in the CoCrFeNiV coating,which formed a"soft matrix-hard particle"synergistic strengthening structure with the FCC phase,inhibiting the initiation and propagation of cracks.Meanwhile,V accelerated the formation of oxide films during the wear process and the formed lubricating layer further improved the wear resistance of the coating.This study confirms that adding V can significantly enhance the comprehensive wear resistance of high-entropy alloy coatings,providing a new idea for the design of wear-resistant coating materials.