Effect Of Trace Element C On The Microstructure And Properties Of AlCrCuFeMn_x High-Entropy Alloy

At present,high-entropy alloy is a major research focus in the field of metal materials.Compared with traditional alloys,it has high strength,high plasticity,good wear resistance and corrosion resistance.However,in high-entropy alloys,single-phase BCC alloys have higher strength and hardness,but lower plasticity.The single-phase FCC alloy has good plasticity but low strength.One of the advantages of high entropy alloys is the designability of the components.The different types and contents of the alloy elements will affect the microstructure and mechanical properties of the alloys.As a stable austenitic phase element,Mn can effectively improve the plasticity of the alloy.Because of its small atomic radius,while C is easy to form interstitial solid solution in the alloy matrix and has a large negative mixing enthalpy with Cr,Mn and other alloying elements,which can easily form a hard and brittle carbide phase and can effectively enhance the strength of the alloy.Therefore,in order to overcome the problem of strength-plasticity trade-off of high-entropy alloy,this work selects AlCrCuFeMn high-entropy alloy with co-existing FCC phase and BCC phase in the matrix,combines with low alloying strategy,and adjusts the content of alloying elements,so that the strength and plasticity of high entropy alloy can be improved synergistically.The effects of Mn and C contents on microstructure and mechanical properties of AlCrCuFeMn high-entropy alloy were investigated.In this paper,AlCrCuFeMn_x（x=0,0.5,1,1.5,2）,AlCrCuFeMn C_x（x=0,0.025,0.05,0.075,0.1,0.125）and AlCrCuFeMn_1.5C_x（x=0,0.025,0.05,0.075,0.1,0.125）high-entropy alloys ingots were prepared by vacuum electric arc melting furnace,the organisation and mechanical properties of the alloys were analysed and tested using XRD,scanning electron microscopy and transmission electron microscopy as well as microhardness tester,friction and wear tester and electronic universal testing machine.The following conclusions were drawn:（1）AlCrCuFeMn_x（x=0,0.5,1,1.5,2）has a typical dendritic structure,which consists of a BCC structured dendrite,an FCC structured interdendrite,and precipitates with an ordered BCC structure precipitated within the dendrite.The Mn element can enter into the dendritic,interdendritic,and precipitate tissues,and it has a good affinity for the three.As the Mn element content increases,the size of the precipitated phase nanoparticles in the dendritic region first increases and then decreases,the area fraction increases initially and decreases afterwards,the strength and wear resistance of the alloy decreases,and the plasticity increases.The AlCrCuFeMn_1.5 alloy has the best comprehensive mechanical properties with a hardness of 360 HV and a wear rate of 2.4×10^-5 mm³N^-1mm^-1,Its yield strength,compressive strength,and deformation amount are 960 MPa,1700 MPa,and 27.5%respectively.（2）In AlCrCuFeMn C_x（x=0,0.025,0.05,0.075,0.1,0.125）high-entropy alloys,when the carbon content x<0.075,the alloy has a typical dendrite structure,in which the dendrite is BCC structure and the intergranular organization is FCC structure;when the carbon content x≥0.075,the M₇C₃ phase is formed in the alloy,mainly distributed in the dendrite organization.The lattice constant of the BCC phase increases with the increase of carbon content and then decreases,reaching a maximum value of 2.9062nm at x=0.075.With the increase of carbon content,the hardness and strength of the alloy are improved,while the plasticity increases and then decreases.The AlCrCuFeMn C_0.125 alloy has the best comprehensive mechanical properties with a hardness of 470 HV and a wear rate of 1.01×10^-5 mm³N^-1mm^-1,Its yield strength,compressive strength,and deformation amount are 1180 MPa,1480 MPa,and 15.4%respectively.（3）The organisation and microstructure of the AlCrCuFeMn_1.5C_x high-entropy alloy is approximately the same as that of the AlCrCuFeMn C_xhigh-entropy alloy,but the increased Mn content in the alloy increases the solid solution of C atoms in the alloy matrix and increases the lattice constant of the alloy matrix.From the performance point of view,the simultaneous increase of Mn content and C content lead the hardness and wear resistance of the alloy increase significantly,while the plasticity decreases sharply and the alloy transforms into a brittle material.The AlCrCuFeMn_1.5C_0.075 high-entropy alloy has the highest hardness with a value of 1300HV and a wear rate of 1.6×10^-6 mm³N^-1mm^-1,which can be applied to high-entropy alloy wear coatings.When the carbon content x>0.075,the plasticity of the alloy increases,while the hardness and wear resistance gradually decreases.The AlCrCuFeMn_1.5C_0.1 alloy has the best comprehensive mechanical properties with a hardness of 620 HV and a wear rate of 1.45×10^-5 mm³N^-1mm^-1,Its yield strength,compressive strength,and deformation amount are 1190 MPa,1780 MPa,and 18.5%respectively.