Preparation And Mechanical Properties Of AlTi Doped CrCoNi Based Medium Entropy Alloy

The development of metal materials with high strength and good ductility has long been a challenging goal in modern engineering applications.High entropy alloy is a new type of alloy proposed in recent years,which is different from the traditional alloy design concept.Because of the mixed characteristics of various elements,it has excellent performance,so it has great development potential in the field of engineering application.Medium entropy alloy is a branch refined on the basis of the concept of high entropy alloy proposed.The mixing entropy of medium entropy alloy is lower than high entropy alloy,and the number of pivot elements is small.CrCoNi alloy has good toughness,which provides a large plastic sacrifice space for obtaining high strength alloy.Therefore,this paper selects CrCoNi alloy for research,and uses traditional alloy strengthening methods to prepare strong plastic equilibrium alloy materials.In this study,vacuum arc melting was used to create the original mesentropic CrCoNi alloy,（CrCoNi）₉₇Al_xTi_3-x（x=1.0,1.5,and 2.0）,and（CrCoNi）₉₄Al_3.0Ti_3.0.The mechanical properties of the materials were also analyzed,characterized,and tested using XRD,SEM,mechanical universal testing equipment,and Hopkinson bar system.The effects of different ratios of Al and Ti elements on the grain structure and strong plasticity of CrCoNi medium entropy alloy were studied.Secondly,（CrCoNi）₉₇Al_1.0Ti_2.0 medium entropy alloy sheet with thickness of about 12.5 mm was obtained by multi-pass cold rolling process.The rolled plate was then annealed at various temperatures.The microstructure and characteristics of the medium entropy alloy（CrCoNi）₉₇Al_1.0Ti_2.0 were examined in relation to the effects of cold rolling plastic deformation and annealing treatment.The as-cast（CrCoNi）₉₇ Al_xTi_3-x（x=1.0,1.5,2.0）and（CrCoNi）₉₄Al_3.0Ti_3.0 alloys were shown to a single face-centered cubic（FCC）structure despite changes in the alloys’strength and plasticity.The plastic elongation of（CrCoNi）₉₇Al_1.0Ti_2.0 alloy is enhanced by 35%from60.2%to 81.4%,and the strength of the alloy is 9.4%lower than that of the original CrCoNi alloy.The rolled（CrCoNi）₉₇Al_1.0Ti_2.0 alloy has clearly undergone work hardening,and as a result,its strength and hardness have greatly increased while its ductility and toughness have significantly decreased.The rolled alloy has a significant amount of L1₂ second phase after annealing at 800°C to 900°C.With tensile strength and elongation of 1106MPa and 33.5%,respectively,the rolled（CrCoNi）₉₇Al_1.0Ti_2.0 alloy exhibits better overall attributes.At medium and high strain rates,it is discovered that the compressive yield strength of the CrCoNi medium entropy alloy is approximately 100MPa higher than that of the quasi-static alloy.Finally,by doping Al and Ti alloying elements,this paper provides effective elements for the formation of a coherent precipitated phase of CrCoNi medium entropy alloy.Combined with cold deformation and heat treatment,a CrCoNi base medium entropy alloy with a good combination of strength and elongation is obtained.