Preparation And Properties Of FeNiCoCr-based High-entropy Alloy Coatings

Surface modification technology can be used to improve the comprehensive properties of 316stainless steel.As an emerging material,high-entropy alloys have gradually become a good choice for surface modification materials due to their excellent properties.In terms of surface modification technology,laser cladding technology is widely used in the preparation of high-entropy alloy coatings due to the advantages of high energy density,fast solidification rate,small thermal impact on the matrix,and low dilution rate.FeNiCoCr high-entropy alloys have always been a hot research topic due to their good plasticity and fracture toughness,but their poor mechanical strength limits their application range.Mo and Nb,as large-sized high melting point elements,can not only strengthen the coatings but also further improve the corrosion resistance of the coatings.In order to improve the comprehensive performance of 316 stainless steel,in this paper,FeNiCoCrMox（x:molar ratio,x=0,0.15,0.20,0.25）and FeNiCoCrNbx（x:molar ratio,x=0,0.1,0.2,0.3）high-entropy alloy coatings were prepared on the surface of 316 stainless steel by laser cladding.The phase composition,microstructure,crystallography,microhardness,dry sliding friction and wear properties and corrosion resistance of the prepared high entropy alloy coatings were characterized by X-ray diffractometer,scanning electron microscope,electron backscatter diffractometer,microhardness tester,friction and wear tester,white light interferometer and electrochemical workstation.The following conclusions are drawn:FeNiCoCrMox（x:molar ratio,x=0,0.15,0.20,0.25）high-entropy alloy coatings exhibited a single FCC solid solution structure accompanied by a typical dendritic（DR）-interdendritic（ID）structure.The microhardness of Mo0,Mo0.15,Mo0.20 and Mo0.25 high-entropy alloy coatings were increased by 70.1%,77.0%,84.9%and 90.5%,respectively,compared with the substrate.Dry sliding friction and wear tests show Mo0.25 high-entropy alloy coating has the lowest average friction coefficient and the best wear resistance.Compared with Mo0 high-entropy alloy coating,the specific wear rates of Mo0.15,Mo0.20 and Mo0.25 high-entropy alloy coatings decreased by11.1%,27.8%and 38.9%,respectively.The electrochemical test results show that the corrosion type of the coating is intergranular corrosion.In addition,the Mo0.20 high-entropy alloy coating exhibits the best corrosion resistance due to the enhancement effect of MoO₃ on the Cr₂O₃passivation film.In FeNiCoCrNbx（x:molar ratio,x=0,0.1,0.2,0.3）high-entropy alloy coatings,the addition of Nb increases the lattice constant of the system.When x=0.3,lamellar Laves phases appear at ID.The grains in the four high-entropy alloy coatings showed random orientation,and the increase of Nb achieved grain refinement.The microhardness of the Nb0,Nb0.1,Nb0.2 and Nb0.3 high-entropy alloy coatings are 1.78,2.19,2.30 and 2.37 times that of the 316 stainless steel substrate,respectively.The specific wear rates of the Nb0,Nb0.1,Nb0.2,Nb0.3 high-entropy alloy coatings are 0.36,0.24,0.22 and 0.20 mm³/Nm,respectively.The wear resistance of the coatings are improved.Both 316 stainless steel and Nb0.3 high-entropy alloy coating exhibit p-type semiconductor characteristics.The corrosion current density of the Nb0.3 high-entropy alloy coating is 2.46×10^-9 A/cm²,and the width of the passivation zone is twice that of 316 stainless steel.