Effect Of Intersitial Carbide On Microstructure And Properties Of CoCrFeNiV_0.5C High Entropy Alloy

An alloy containing five or more elements in an isoatomic or non-isoatomic ratio,with an element content of 5 to 35 at.%is named High-entropy alloys?HEAs?.First of all,in this paper,CoCrFeNiV_0.5 high-entropy alloy with face-centered cubic?FCC?structure and low strength and good shaped at room temperature is used as the matrix alloy,and its microstructure and properties are improved by alloying with carbon element.Secondly,the effects of different processing techniques on CoCrFeNiV_0.5C_x high-entropy alloys at low carbon content and the effects of different types of interstitial carbides on the alloy after heat treatment were systematically studied.The results show that the addition of element C changes the structure of the CoCrFeNiV_0.5C_x high-entropy alloy from the original coarse single-phase FCC structure equiaxed crystal to a typical dendrite structure.Among them,the interdendritic regions?ID?carbide precipitated phase VC,the dendrite regions?DR?still maintains the FCC structure,and the interstitial carbide precipitated phase and the matrix phase show a coherent relationship.As the volume fraction of the carbide precipitated phase gradually increases,the strength and hardness of the alloy gradually increase,and the shape is gradually reduced,and a more balanced performance is obtained in the C0.15 alloy.The yield strength,tensile strength and fracture strain are 603 MPa,785 MPa,and 21.8%,respectively.The nanohardness of the carbide precipitation phase and the FCC phase are12 GPa and 5 GPa,respectively,and the elastic modulus values are 220 GPa and 205 GPa,respectively.The CoCrFeNiV_0.5C_x high-entropy alloy with lower carbon content was processed by hot rolling,homogenizing heat treatment,cold rolling,and medium temperature heat treatment.The alloys in all states other than the medium temperature heat treatment have FCC single-phase structure,no carbide phase is precipitated,and the carbon element is dissolved in the solid solution structure.For the alloy after medium temperature heat treatment,no carbides were generated at 600?,and interstitial carbide M₇C₃ was generated at 700?and 800?.The 2C and 3C alloys annealed at 700?obtained excellent mechanical properties.Their yield strengths??_y?were 1339.7 MPa and 1264.6MPa,respectively,and their breaking strains??_f?were 7.64%and 6.38%,respectively.Further analysis of the alloy found that more interstitial carbides M₇C₃ existed at the boundary between the incompletely recrystallized region and the completely recrystallized region.There is also a new generation of ordered interstitial carbides?M_xC_y?of non-stoichiometric carbon vacancy configuration in the fully recrystallized region.The improved performance of the alloy has an important relationship with this newly-formed interstitial carbide,which provides particles for the formation of dimples and enhances the plasticity of the alloy.