Microstructures And Mechanical Properties Of Fe_100-x（CoCrNiMn）_x Alloys

Recently,the research and development of high-entropy alloys（HEAs）have been become a hot spot in the field of metal materials.Based on the alloy design concepts of HEAs and“metastable engineering”,a high strength alloys with good toughness was obtained.In this work,FeCoCrNiMn multi-component alloys with different CoCrNiMn contents were prepared.The microstructures,phase structures,phase distributions and mechanical properties of the cast alloys were systematically studied by XRD,SEM,EDS,EBSD,TEM,tensile and micro-hardness tests.Meanwhile,the deformation of Fe₆₇Co_8.25Cr_8.25Ni_8.25Mn_8.25 alloy with special work hardening rate was studied.In Fe_100-x（CoCrNiMn）_x（x=13⁸0）alloys system,with the decrease of the content of solid solution element CoCrNiMn,the microstructure changes from dendrite to dendrite+equiaxial crystal,and finally to dendrite+lath structure;the structures are successively transformed from FCC structure to BCC structure alloys which can divide into FCC single-phase,dual-phase alloys and BCC single-phase alloys,and the microstructures of FCC single-phase alloys,dual-phase alloys and BCC single-phase alloys are developed dendrite,dendrite+equiaxial crystal and dendrite+lath structure,respectively.EDS analysis of Fe67alloy shows that the elements distribution between dendrite and indendrite are not uniform,in which Fe is enriched in dendrite,Mn and Ni are enriched in indendrite,Co Cr are uniformly distributed.EDS analysis of Fe81 alloy shows that the elements distribution between the lath structure on dendrite and the matrix is uniform.In terms of mechanical properties,FCC single-phase alloys have excellent plasticity but low strength.With the decrease of CoCrNiMn content,the tendency of strength,micro-hardness and plasticity are first decreases and then increases,increases and decreases in the dual-phase alloys,respectively.In the BCC single-phase alloys,the tendency of strength and micro-hardness are both first decreases and then increases and the plasticity is increases.Deformation induced phase transformation has obtained in Fe67 alloy in which the phase fraction of FCC and BCC are decrease and increase,respectively.The BCC structural fine grain nucleates and grows in the coarse grain of FCC structure.The grain orientation between fine grain with BCC structure and the coarse grain of matrix is different and connected by large angle grain boundary,which significantly improves the work hardening rate of Fe67 alloy.