Study On Impact Deformation Behavior Of FeCoCrNiC_x High Entropy Alloys

High-entropy alloys are generally consists of at least five or more alloy elements,and its unique design concept endows high-entropy alloys with excellent properties,such as high strength,high hardness,good plasticity,excellent toughness and thermal stability,potential high-temperature and low-temperature properties.In the research of mechanical properties of high-entropy alloys,most investigations on the mechanical behavior of high-entropy alloys are based on the quasi-static loading,but the deformation behavior of high-entropy alloys under dynamic loading are rarely.Therefore,the research work in this area needs to be carried out.In this paper,Fe Co Cr Ni C_x（x=0.04,0.08,0.15,0.20）high entropy alloys were prepared by high vacuum arc melting furnace.The effect of C content on the microstructure of Fe Co Cr Ni C_x alloy were studied through XRD,optical microscopy,SEM and EDS.The Vickers hardness of the alloys were measured by microhardness tester.The mechanical properties of the alloys at different strain rates were investigated by quasi-static and dynamic mechanical tests using a universal compression testing machine and separate Hopkinson compression bar（SHPB）,the stress-strain curves at strain rate of 0.001s^-1 and the true stress-true strain curves at strain rate of 2300 s^-1～5600s^-1 were drawn,and the effect of strain rate on plastic deformation of materials were analyzed.the J-C constitutive equations of the material were established.The microstructure of the alloys after high strain rate impact were analyzed.The results show that the as-cast Fe Co Cr Ni C_x high entropy alloys are mainly composed of FCC phase and carbide phase.The hardness and strength of the alloys are obviously improved due to the lattice distortion caused by the solution of C element in the alloys matrix.Under quasi-static and dynamic loading,alloys exhibit obvious work-hardening behavior and good plastic deformation ability.The work hardening index of the alloys are increasing,the present high-entropy alloys exhibit the higher strain rate sensitivities（SRS）under dynamic compression.The true stress and true strain curves of alloys fluctuate in the plastic deformation stage,which are the result of the competition between work hardening and adiabatic temperature rise.Based on Johnson-cook（J-C）model,the constitutive equations of high entropy alloys under dynamic loading are established.The adiabatic shear band and a large number of slip bands were observed in the Fe Co Cr Ni alloy,and cracks were formed in the adiabatic shear band,no obvious cracks and adiabatic shear bands were observed in the deformed C_0.20 alloy,and the structure of the alloy was not damaged.