High Temperature Deformation Behavior And Mechanical Properties Of CoCrFeMnNiCx High Entropy Alloy

Compared with the crystal structure system of conventional alloys,high entropy alloys are a relatively new class of materials.It is based on four or more elements with approximately equimolar concentration.After a reasonable combination of elements,it can have excellent composite properties such as high strength,high melting point and corrosion resistance.In this study,Co Cr Fe Mn Ni high entropy alloy with better ultra-low temperature toughness is selected,and the strength and other mechanical properties of the alloy are enhanced by adding non-metallic C elements which is good affinity to the Co Cr Fe Mn Ni high entropy alloy.The purpose is to broaden its use fields.Gleeble thermal simulation experiment and room temperature tensile experiment were used to study the high temperature deformation behavior and room temperature mechanical properties of materials with different C contents.Based on the results of Gleeble thermal simulation experiments,the constitutive equations of Co Cr Fe Mn Ni C_0.5 high entropy alloy and Co Cr Fe Mn Ni C₅ high entropy alloy were established based on the Arrhenius hyperbolic sine model and the accuracy of the constitutive equation was verified.At the same time,according to the theory of dynamic material model(DMM),the hot working drawings of Co Cr Fe Mn Ni C_0.5 high entropy alloy and Co Cr Fe Mn Ni C₅ high entropy alloy were established.Based on the judgment of the Prassad instability criterion,the optimal hot working process range for Co Cr Fe Mn Ni C_0.5 alloy is high speed zone:950-1000 ?/10^-1.2-1 s^-1,low speed zone:825-1000 ?/10^-3-10^-1.7s^-1.Co Cr Fe Mn Ni C₅ high entropy alloy has the best hot working process range under the current experimental conditions of 900-1000 ?/10^-3-10^-2.6s^-1.By studying the high-temperature deformation behavior of Co Cr Fe Mn Ni C_0.5 high entropy alloy and Co Cr Fe Mn Ni C₅ high entropy alloy,the different deformation mechanisms under different Zener-Hollomon parameter values are discussed.It was found that the addition of C element effectively weakened the dislocation cross-slip ability,and caused the transition of the density dislocation wall structure in the matrix to the microband structure,causing work hardening during thermal deformation.The strain stress of Co Cr Fe Mn Ni C₅ high entropy alloy under different deformation conditions is higher than that of Co Cr Fe Mn Ni C_0.5 high entropy alloy.The pinning effect of higher levels of carbides on dislocations enhances the interactions among dislocations such as overlap,stacking,and entanglement,while expanding the strain of dislocation motion,resulting in higher yield strength.During the rheological softening phase,carbide particles precipitate in the axial plastic deformation region,and as the recrystallization nucleation particles in the later stage of deformation,the recrystallization softening mechanism is promoted.The phase composition of CoCrFeMnNiCx(X=0,0.5,1,3,5)high entropy alloys with different C contents was studied.In the as-cast condition,when X<5,the phase structure is the single FCC crystal struture;when X=5,the phase structure is the FCC solid solution phase and M₇C₃ intermetallic compound phase.After rolling and annealing,when X=3,carbide particles precipitated in the matrix,and the alloy consisted of FCC solid solution phase and M₇C₃ phase.When X=5,the alloy is composed of FCC solid solution,M₇C₃ second phase and M₂₃C₆ second phase.The room temperature mechanical properties test showed that as the carbon content increased from 0 at.%to 3 at.%,The tensile yield strength increased from 371 MPa to792 MPa.Co Cr Fe Mn Ni C₁high entropy alloy has the best mechanical properties.The tensile yield strength is 634 MPa and the elongation is 38%.The Co Cr Fe Mn Ni C₅ high entropy alloy deformed at 800 ?/10^-1 s^-1 has a vickers hardness of up to 345 HV,which is 118%higher than the Co Cr Fe Mn Ni high entropy alloy 158 HV.