Composition Design And Toughening Of Al_0.1CoCrFeNi-M High Entropy Alloys

High entropy alloy has become a research hotspot of researchers in recent years because of its high strength,high plasticity,good thermal stability,wear resistance,corrosion resistance and other excellent properties.Through the continuous efforts of researchers,it has achieved many major successes and made major breakthroughs in the field of materials,but there are still many key problems to be solved.For example,the single-phase body centered cubic（BCC）high entropy alloy has excellent yield strength and excellent strength performance,but its poor plasticity,poor fluidity and other factors have not been widely used in real life;FCC high entropy alloys have excellent toughness and plasticity,but their strength is generally at a relatively low level.The goal of this project is to design a high strength,high plasticity and high entropy alloy with FCC high entropy alloy as the matrix through element doping composition design,which can meet the needs of use in both shape and strength,and further improve the microstructure and mechanical properties of the alloy through machining and heat treatment.Based on the previous composition design,Al_0.1CoCrFeNihigh entropy alloy with single FCC phase structure is selected as the matrix composition.By adding different large atomic radius elements and small atomic radius elements for composition modification,the changes of microstructure and properties were studied,and the alloy components with the best mechanical properties were selected for machining and heat treatment.By adding large atomic radius replacement alloying elements represented by Ti,Nb and Zr,we found that the microstructure of Al_0.1CoCrFeNiTi_x series alloys changed from single-phase fcc structure(x=0,_0.1)to fcc structure solid solution +bcc structure(_0.1<x ≤ 0.4).With the increase of Ti content,the strength of the alloy increases and the plasticity decreases to a certain extent.Ti01 alloy has the best comprehensive tensile properties,its tensile yield strength is 630 mpa,and its elongation at fracture reaches20%.With the addition of Nb,the microstructure of the alloy is a process from the initial single-phase FCC solid solution to hypoeutectic structure,then to complete eutectic structure,and finally to hypereutectic structure.Fe₂ Nb type Laves phase appears in the eutectic structure,which is a C14 type complex close packed hexagonal structure.Among them,nb01 has the best comprehensive properties,the tensile strength is 620 MPa,and the elongation at fracture is 27%.The addition of Nb increases the volume fraction of Laves phase,which has a significant strengthening effect on the mechanical properties of the alloy,but its plasticity also becomes worse.After adding Zr,the alloy gradually changes from hypoeutectic structure to eutectic structure（Zr02,zr03）After adding a small amount of Zr,the strength of zr01 and Zr02 alloys is enhanced to a certain extent.The yield strength of Zr02 alloy reaches 750 MPa.At the same time,the plasticity of the alloy remains very good,and the compression rate reaches more than 50%.When the content of Zr continues to increase,the strength of zr03 and zr04 alloys increases significantly,and the plasticity decreases.The yield strength of zr03 alloy is about 1000 MPa,and the compression deformation rate is 34%With the addition of C element,the yield strength of the alloy increased significantly.The tensile strength of C01 alloy reached 600 MPa,while the plasticity remained good,and the elongation reached 45%.The tensile strength of C02 alloy reached 790 mpa,the plasticity decreased to a certain extent,and the elongation was22%.The plasticity of C04 alloy deteriorated rapidly due to excessive carbide precipitation.After rolling,the strength of al_0.1cocrfenic_0.1 increases dramatically,and the plastic realization is not good.Annealing at different temperatures improves the plasticity of the alloy,and the strength of the alloy is maintained to a certain extent.Among them,annealing at 800 ℃ has good performance,with tensile strength of1100 mpa and elongation of 12%;After annealing at 1200 ℃,the plasticity is improved obviously,the elongation reaches 32% and the tensile strength is 680 mpa.After cold rolling and annealing,Al_0.1CoCrFeNiTi_0.1 also formed new intermetallic compounds σ Phase,the microstructure in the annealed samples has undergone severe deformation,and local recrystallization first occurs near the shear band.With the increase of temperature,the degree of recrystallization in the samples also increases until the fully recrystallized equiaxed grains are displayed.At the same time,a large number of annealing twins appeared in the alloy during annealing.After volume rolling,the strength of al_0.1cocrfeniniti_0.1 alloy has been greatly improved,and the loss of plasticity is very obvious.At 600 ℃,the tensile strength of the alloy has increased slightly.With the increase of annealing temperature,the strength of the alloy decreases and the plasticity improves obviously.The tensile strength of an-1200 alloy is 900 MPa,and the fracture elongation is more than 40%.After rolling and heat treatment,the microstructure of al_0.1cocrfeninb_0.1 alloy has no obvious change,no new phase is formed,and the microstructure is stable.After annealing at different temperatures,the strength and plasticity of the alloy change little at low temperature.With the increase of temperature,the strength of the alloy decreases and the plasticity is improved.The tensile strength of an-1000 alloy reaches 700 MPa and the fracture elongation reaches 20%.