Research On Microstructure And Properties Of FeCoCrNiMo_x High Entropy Alloy

Compared with the performance of traditional alloys,high-entropy alloy has good properties such as high thermal stability,high strength,high hardness,high wear resistance and strong corrosion resistance.The microstructure of the alloy can be optimized by adjusting the composition design of the high-entropy alloy,so as to achieve the purpose of improving the Comprehensive performance of the alloy.In recent years,high-entropy alloy exhibits great potential for development in key areas of military defense,aerospace,power and other energy sources.In this paper,Fe Co Cr Ni Mo_x high-entropy alloys were prepared by two processes.The structure and properties of high-entropy alloy were explored.First,combining the high-entropy alloy composition design concept,the as-cast Fe Co Cr Ni Mo_x(x=0.0,0.5,1.0,1.5,molar ratio)high-entropy alloys were prepared by vacuum arc furnace smelting.The phase structure of the as-cast high-entropy alloys is predicted by Thermo-Cale thermodynamic calculation software.The calculation results show that Fe Co Cr Ni alloy may form face-centered cubic(FCC)single phase after solidification,Fe Co Cr Ni Mo_x(x=0.5,1.0)may form FCC+?phase and Fe Co Cr Ni Mo_1.5may form FCC+?phase+?phase.The microstructure of the as-cast alloy was studied by OM,XRD,SEM,EDS,TEM and other methods.The results showed that the as-cast Fe Co Cr Ni high-entropy alloy was an island-shaped face-centered cubic single phase and Fe Co Cr Ni Mo_x(x=0.5,1.0,1.5)all form dendritic structure.Fe Co Cr Ni Mo_x(x=0.5,1.0)is a combination of FCC phase and eutectic structure(FCC phase+?phase)and the?phase is a(Cr-Mo)-rich phase.Fe Co Cr Ni Mo_1.5 is a combination of?phase which is precipitated first and eutectic structure(FCC phase+?phase+?phase).With the addition of Mo content,the as-cast high-entropy alloy increases the lattice distortion and the lattice constant.The microhardness of as-cast Fe Co Cr Ni Mo_x was tested.Fe Co Cr Ni high-entropy alloy has lower hardness.With the addition of Mo,the hardness of as-cast high-entropy alloy increases significantly.The electrochemical test of as-cast Fe Co Cr Ni Mo_x was carried out in 0.5 mol/L H₂SO₄ and 3.5 wt.%Na Cl.The corrosion resistance of the as-cast high-entropy alloy in the 0.5 mol/L H₂SO₄environment increased first and then decreased with the increase of the Mo element content.Mo_0.5 has the best corrosion resistance.The corrosion resistance in 3.5 wt.%Na Cl decreases with the increase of Mo content.The high-temperature oxidation resistance of as-cast Fe Co Cr Ni Mo_x high-entropy alloys at 1000?were studied by thermogravimetric analysis(TGA)method.The results show that the high-temperature oxidation resistance of high-entropy alloy increases with the increase of Mo content.Secondly,the coating composition interval selection was optimized,and the Mo element mole fraction was selected in the composition interval of 0-0.8 for laser cladding experiments.Fe Co Cr Ni Mo_x(x=0.0,0.2,0.4,0.6,0.8,molar ratio)high-entropy alloy coating was prepared by laser cladding.The microstructure of high-entropy alloy coatings was studied by OM,XRD,SEM,EDS and other testing methods.The research results show that the Fe Co Cr Ni Mo_x(x=0.0,0.2,0.4)high-entropy alloy coating has a face-centered cubic structure and an equiaxed crystal structure is formed on the surface.Fe Co Cr Ni Mo_x(x=0.6,0.8)high-entropy alloy form FCC phase and?phase that the?phase is concentrated in the intergranular position.The surface of the Fe Co Cr Ni Mo_x(x=0.6,0.8)high-entropy alloy coating shows obvious dendritic structure morphology.The microhardness of the cross section of the high-entropy alloy coating was tested.The hardness of the high-entropy alloy coating from the 45#steel substrate has increased significantly.With the addition of Mo,the hardness of the high-entropy alloy coating has increased significantly.The corrosion resistance of laser cladding high-entropy alloy coating in 0.5 mol/L H₂SO₄ environment and 3.5 wt.%Na Cl environment increases steadily with the increase of Mo content and decreases when the Mo content exceeds 0.6.Fe Co Cr Ni Mo_0.6 alloy coating shows the best corrosion resistance.