Study On Microstructure And Properties Of FeCoNi₂CrMnV_0.5Nb_x High Entropy Alloy Coatings By Laser Cladding

High-entropy alloy is a new type of alloy composed of five or more elements and the mole fraction of each element is between 5%and 35%.Due to its special thermodynamics,crystallography,kinetic and cocktail effects,high-entropy alloys have the characteristics that many traditional alloys do not have.Laser cladding is a new type of surface modification and additive manufacturing technology.It has the characteristics of high precision,strong controllability,little thermal impact on the substrate,and tight bonding between the cladding layer and the substrate.In this paper,FeCoNi₂CrMnV_0.5Nb_x（x=0,0.4,0.6,0.8,1.0,1.2）high-entropy alloy coatings were fabricated on the ZG25Mn Ni cast steel by laser cladding.The microstructure of the high-entropy alloys were characterized.Wear resistance and corrosion resistance of the high-entropy alloy coatings were tested.The influence of parameters on the high-entropy alloy coating was explored by the optimization experiment of laser cladding.The results showed that,with the increasing of welding power,the penetration width,penetration depth and the dilution rate of FeCoNi₂CrMnV_0.5Nb_x high-entropy alloy coating increased gradually.With the increase of welding speed,the penetration depth,penetration width and the dilution rate showed a decreasing trend.The dilution rate had an effect on the composition,microstructure and properties of the high-entropy alloy coating.When the laser power was 1100W～1200W and the scanning speed was 0.006 m/s,the formation of the high-entropy alloy coating was formed well,the high-entropy alloy powder was completely melted,there were no defects such as pore cracks,and it had a low dilution rate.The FeCoNi₂CrMnV_0.5 high entropy alloy coating obtained by laser cladding was a typical single-phase columnar crystal structure,which was composed of FCC phase.After adding Nb element,FeCoNi₂CrMnV_0.5Nb_x high entropy alloy coating transformed into dendrite structure.The dendrite was FCC phase,and interdendritic was eutectic structure composed of FCC phase and Laves phase.Nb element was enriched in the intercrystalline eutectic structure.The content of laves phase gradually increased with the increasing of Nb content,and the high-entropy alloy changed from hypoeutectic structure（x<1.0）to eutectic structure（x=1.0）,hypereutectic structure（x>1.0）,and the primary phase was also transformed from FCC phase solid solution to Laves phase.With the increase of Nb element content,the microhardness of FeCoNi₂CrMnV_0.5Nb_x high-entropy alloy coating increased gradually,and the friction coefficient and wear amount decreased gradually.When the Nb content x=1.2,the microhardness of the upper part of the coating reached 631.1 HV,which was 4 times and 2 times higher than that of the base metal and FeCoNi₂CrMnV_0.5 high-entropy alloy coatings,and the wear resistance was 14.2 times and 9 times that of the base metal and FeCoNi₂CrMnV_0.5 HEA coating.The corrosion resistance of FeCoNi₂CrMnV_0.5Nb_xhigh-entropy alloy coating in 3.5 wt.%NaCl solution is better than ZG25Mn Ni cast steel and FeCoNi₂CrMnV_0.5 high-entropy alloy coating.With the increasing of Nb content,the corrosion resistance of coatings first increased and then weakened.When the Nb content x=0.8,FeCoNi₂CrMnV_0.5Nb_x High-entropy alloy coatings had the best corrosion resistance.