Effect Of Carbon On Microstructure And Properties Of High-entropy Alloys With Different Crystal Structures

High entropy alloy(HEA)is a new type of alloy,which consists of five or more elements in equimolar or near equimolar ratios.The characteristic of multi-principal element makes HEA better than conventional alloys.Due to the interaction between elements,the element contents and species on the microstructures and properties of HEAs have a great effect.So it is very important to understand the influences of the species in HEAs for obtaining HEAs with excellent properties and further scientific research.In this work,the traditional vacuum arc melting technology was employed to synthesize three different crystal structure HEA series,AlFeCoNiCx,(Fe40Mn40Co10Cr10)100-xCx,(Fe40Mn40Co10Ni10)100-xCx and(Fe50Mn30Co10Cr10)100-xCx.X-ray diffraction(XRD),Optical Metallographic Microscope(OM),Scanning Electron Microscope(SEM)and Energy Dispersive Spectrometer(EDS)analysis methods were used to study the effect of alloying elements on the microstructure and mechanical properties of high entropy alloys.The main results as follows:(1)Carbon was added into AlFeCoNi multi-component alloy,and the alloy was transformed from BCC to(BCC + FCC)two-phase.When the carbon content increased to a certain degree,flaky graphite was precipitated in FCC phase.The strength and plasticity of the alloy increased with the increase of carbon content,The compressive strength increased from 1291 MPa to 2875 MPa,and the plasticity increased from 5% to 27% and the alloy was changed from cleavage fracture to quasi-cleavage.(2)The addition of carbon did not change the crystal structure of Fe40Mn40Co10Cr10 and Fe40Mn40Co10Ni10 alloys,but the lattice constant of the alloy increased.In the(Fe40Mn40Co10Cr10)100-xCx alloys,the strength and the plasticity of the alloys increased and decreased with carbon content,respectively.When the carbon content increased to a certain extent,a small amount of Cr7C3 compound was generated from the alloy.In the(Fe40Mn40Co10Ni10)100-xCx alloy,the carbon can significantly improved the strength and plasticity of the alloys.(3)Fe50Mn30Co10Cr10 was consisted of FCC and HCP phase.The addition of carbon promoted the conversion from HCP phase into FCC phase.The volume fraction of HCP phase and the volume fraction of FCC phase decreased and increased with carbon content,respectively.With the addition of carbon,the diffraction peak shifted to the right and the lattice constant reduced.The hardness of the(Fe50Mn30Co10Cr10)100-xCx alloy decreased with the increase of carbon content,but the compressive strength increased with the increase of carbon content.