| Laser cladding technology is an important surface strengthening method to improve the failure of mechanical equipment due to wear and corrosion in extremely harsh environment because of its fast cooling and fast heating,high efficiency and metallurgical bonding between substrate and coating.High entropy alloys with excellent wear resistance,corrosion resistance and good mechanical properties,pay great attention to by scholars both at home and abroad and widely research,in the engineering is often used in extremely harsh service environment,is the preferred material for laser cladding surface strengthening.But high entropy alloys usually exist only because of its high entropy effect in single phase solid solution,this leads to the strength and plasticity mismatch,wear-resisting performance degradation,affect the industrial application.The solution to this problem is to add hard particles to single-phase high entropy alloy.In this paper,using laser cladding on Q235 substrate preparation first CoCrFeNiMo high entropy alloy coating,optimized by central composite design of experiment,effects of laser power,scanning speed and powder feeding speed of coating dilution rate and the influence law of flatness,preparation of coating to obtain the best process parameters,The coatings were subjected to phase analysis,microstructure analysis,microhardness test,friction wear test and electrochemical test.On the basis of the preparation of different WC/CoCrFeNiMo high entropy alloy composite coating,contrast strengthen the WC particles the composite coating was studied the phase structure,microstructure,microhardness,wear resistance and corrosion resistance are studied.In this paper,the main conclusions are as follows:(1)The technological parameters have a great influence on the dilution rate and flatness of the coating,among which the powder feeding speed has the greatest influence on the dilution rate,and the laser power has the greatest influence on the flatness.The dilution rate is positively correlated with the laser power and scanning speed,but negatively correlated with the powder production speed.The flatness is positively correlated with scanning speed and powder feeding spced,and negatively correlated with laser power.The dilution rate and flatness models established are highly reliable.The optimal process parameters were obtained as follows:laser power 480W,scanning speed 1163mm/min,powder feeding speed 0.4r/min.The dilution rate and flatness error of the coating prepared by the cladding experiment were 12.9%and 6.7%,respectively,within the allowable error range.The results show that it is feasible to optimize the process parameters of laser cladding by using center composite design.(2)The prepared high-entropy alloy coating is mainly composed of FCC phase and σ phase,and the microstructure is equiaxed crystal,dendritic crystal and cellular crystal from top to bottom.Coating on average 302.4HV0.3 microhardness and the matrix increase 4.2 times.Coating amount of wear is proportional to the load,when the load is 15N,coating of wear volume was reduced by 71.8%,compared with matrix as main wear mechanism is adhesive wear and oxidation wear;When the load is 20N,the oxide film on the surface of the wear mark is peeled off,and the coating is peeled off.The wear mechanism is mainly abrasive wear,adhesive wear and fatigue wear.In 3.5%NaCl solution,compared with Q235 substrate,the coating has larger Ecorr,smaller Icorr,larger capacitive arc radius,higher impedance modulus in the low frequency region,and better corrosion resistance,which can effectively protect the substrate.(3)CoCrFeNiMo high entropy alloy composite coatings with different WC contents have good cladding effect,no defects such as cracks occurred,the regional characteristics of microstructure and add WC coating did not change obviously,compared the composite coating in the new phase,such as WC,W2C,Co4W2C.The average microhardness of composite coatings is higher than that of coatings without WC,and increases with the increase of WC content.The average microhardness of composite coatings with 30%WC is the highest,reaching 430.7HV0.3,an increase of 42.4%.Under the loading of 15 N,the wear resistance of 20%WC composite coating is the best,and the wear amount is twice lower than that of the coating without adding WC.At this time,the abrasive wear is the main wear,accompanied by a small amount of adhesive wear and oxidation wear.When the loading is 20N,the composite coating of 20%WC does not appear to peel,and the addition of WC particles can significantly improve the wear resistance of the composite coating.Based on the analysis of the polarization curve and impedance,25%WC composite coating corrosion resistance of the optimal. |
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