Microstructure And Properties Of (CoCrFeNiTiSi_x)_100-yWc_y High Entropy Alloy Laser Cladding Coating On Stainless Steel

316L stainless steel as a common engineering structural steel,its surface was usually subject to the damage caused by friction and wear and corrosion leading to surface failure in the course of service.High-entropy alloys,also known as solid solution alloys,are ingeniously designed according to the equiatomic or near equiatomic ratio for multi principal components.They have the characteristics of high hardness and strength,good plasticity and toughness,excellent wear resistance,corrosion resistance and high-temperature oxidation resistance.Moreover,the addition of ceramic particles WC in the high-entropy alloys can not only improve the strength of solid-solution matrix phase,but also provide the important composition conditions for formation of in-situ carbide phase,so as to further enhance the comprehensive properties of the high-entropy alloys.High-entropy alloys cladding coatings of CoCrFeNiTiSi_x(x=0,0.5,1.0,1.5,2.0)and(CoCrFeNiTiSi_2.0)_100-xWC_x(x=0,10,20,30,40 wt.%)were prepared on the surface of 316L stainless steel by laser cladding in order to solve the problem that the surface is vulnerable to damage and fail in severe and complicated service environment.The effects of Si content in CoCrFeNiTiSi_x alloy and WC content on the basis of the alloy system on the formability,microstructure evolution,wear resistance and corrosion resistance of high-entropy alloys coatings were studied,and the optimum composition proportion in high-entropy alloys system was determined.In this paper,the current,the pulse width and the cladding speed were taken as the factors,and the microhardness of CoCrFeNiTiSi_2.0coating was taken as the evaluation index.The experiment with three factors and three levels was designed by Response Surface Method(RSM).The mathematical model for microhardness and current,pulse width as well as cladding speed was established,and the laser cladding process parameters were optimized:current 380 A,pulse width 8 ms and cladding speed 100 mm/min.Under these parameters,549.2 HV_0.2,the highest microhardness of the top layer was achieved.When Si element were added to CoCrFeNiTi coating,with the increase of Si element content,the metallurgical defects such as pores and cracks in the coating were reduced,and the formability was gradually improved.The grain morphology of coatings changed from uniform and fine equiaxed crystal combined with columnar crystal to irregular equiaxed crystal.The phase composition of the coating changed from(Fe,Ni)FCC solid solution phase in the grains and Cr₂Ni₃ phase at the grain boundary to the mixed double phases of(Fe,Ni)FCC solid solution phase combined with(Fe,Cr)BCC solid solution phase in the grains and Co Si₂ phase at the grain boundary;When WC were introduced to CoCrFeNiTiSi_2.0 coating,the coatings with different WC content had good formability and no metallurgical defects such as pores and cracks.The grain morphology of coatings did not change obviously with the increase of WC content,while the content of intergranular precipitates increased gradually.The phase composition changed from the microstructure of CoCrFeNiTiSi_2.0 coating to the mixed double phase of(Fe,Cr)BCC solid solution phase combined with a small amount of(Fe,W,Si)HCP solid solution phase in the grains and intergranular Ti C phase.CoCrFeNiTiSi_2.0 coating of 720 HV_0.2 and(CoCrFeNiTiSi_2.0)₆₀WC₄₀ coating of1040 HV_0.2 were obtained,which was significantly higher than that of the substrate(196 HV_0.2).In the friction and wear experiment,the CoCrFeNiTiSi_2.0 coating with desirable wear resistance significantly reduced the surface damage caused by fatigue wear+adhesion wear+abrasive wear+oxidation wear;The results showed that(CoCrFeNiTiSi_2.0)₆₀WC₄₀ coating performed excellent wear resistance such as good friction and wear coefficient,wear loss and wear scar depth.The wear mechanism was slight adhesive wear+slight abrasive wear+slight oxidation wear,which could further enhance the wear resistance of the high-entropy alloys coatings.In 3.5 wt.%NaCl solution,the open circuit potential,corrosion kinetics parameters in polarization curve,and electrochemical impedance spectroscopy parameters have proved that(CoCrFeNiTiSi_2.0)₈₀WC₂₀ coating possessed the best corrosion resistance;In 1 mol/L H₂SO₄ solution,(CoCrFeNiTiSi_2.0)₆₀WC₄₀ coating showed outstanding corrosion resistance.The equivalent circuit established revealed that the electrode processes of the two coatings were charge transfer processes controlled by electrochemical polarization.