| High-entropy alloy(HEAs)are a new type of material prepared by mixing multiple elements in an equimolar or near equimolar ratio.Since its introduction,it has attracted extensive attention from researchers.This article uses CoCrFeNiAlMox(x=0,0.1,0.2,0.3,0.4,0.5)HE As as the research object;the microstructure and properties of the as-cast and heat-treated alloys are studied.The alloy was heat treated at 600?,800? and 1000? for 12h in a box type resistance furnace and cooled with the furnace.Use vacuum melting method to prepare alloy ingot;heat-treat the alloy through box-type resistance furnace;use X-ray diffractometer,scanning electron microscope,optical microscope,universal testing machine and vickers hardness tester to analyze and discuss the microstructure and mechanical properties.Studies have shown that in as-cast CoCrFeNiAlMox HEAs with different amounts of Mo added,Al is enriched in dendrites,Mo is enriched between dendrites,and the contents of Co,Cr,Fe,and Ni do not change significantly.Due to the large Mo atom size,the crystal structure of the alloy undergoes lattice distortion,resulting in the phase structure of the alloy changing from BCC+NiAl to BCC+NiAl+FCC+Mo element-rich a phase.When the addition amount of Mo element is increased from 0 at.%to 0.5 at.%,a large number of rod-shaped and spherical structures are generated in the dendrite region of the as-cast CoCrFeNiAlMox HEAs,and the granular alpha phase is precipitated between the dendrites,resulting in increased hardness,and compressive strength and plasticity are reduced.The CoCrFeNiAl HEAs precipitated the ?1 phase rich in Cr after heat treatment at 600?and 800?.The effect of heat treatment on its structure is small;after heat treatment at 1000?,the compressive strength and plasticity of the alloy reached the best,1735.6MPa and 19.3%,respectively.The hardness reaches the highest after heat treatment at 600?,which is 711HV.The CoCrFeNiAlMo0.1 HEAs formed a new BCC phase after heat treatment at 800?.The structure change is not obvious;its hardness,compressive strength and plasticity all show the trend of increasing first and then decreasing,reaching the highest after heat treatment at 600?,respectively 2138.6MPa and 21.5%and 910HV.After heat treatment,the structure change of CoCrFeNiAlMo0.2 HEAs is small,and the volume fraction of dendrite gradually increases.After heat treatment at 1000? for 12h,the compressive strength and plasticity are the best,1590.5MPa and 16.9%,respectively.The hardness of the alloy increases first and then decreases,reaching the best after heat treatment at 600?,which is 950HV;After heat treatment,the CoCrFeNiAlMo0.3 HEAs coarsens the dendrites,and the network structure is distributed in the interdendritic region;the compressive strength and plasticity are the best after heat treatment at 1000?,respectively 1734.9MPa and 18.4%.The hardness of the alloy increases first and then decreases,and reaches the best after heat treatment at 600?,which is 980HV.After heat treatment,the structure of CoCrFeNiAlMo0.4 HEAs is rod-shaped dendrites,and lamellar and network eutectic structures are formed between the dendrites.After heat treatment at 1000? for 12h,its compressive strength and plasticity reached the highest,respectively 2050.2MPa and20.0%;the hardness of the alloy first increased and then decreased,and reached the best after heat treatment at 800?,which was 1063HV.After heat treatment at 1000?,the ? phase of CoCrFeNiAlMo0.5 HEAs decreases,and Cr4.6MoNi2.1 intermetallic compounds are precipitated.With the increase of the heat treatment temperature,the dendrites are gradually refined and arranged in an orderly manner,and the volume fraction of the area between the dendrites increases.After heat treatment at 800?,the compressive strength,plasticity and hardness were significantly improved,which were 2100.5MPa,21.6%and 1113HV,respectively. |
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