Study Of Thermodynamic And Elastic Properties Of High Entropy Alloy Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀

As new class of metallic materials,high-entropy alloys（HEAs）have attracted plenty of attention over the past decade due to their excellent properties.From the standpoint of crystal structure,compared with face-centered cubic（FCC）or body-centered cubic（BCC）structure,hexagonal close-packed（HCP）structure is rarely found in the single-phase random solid solution of HEAs,and most existing HCP HEAs are composed of rare earth（RE）elements.As a novel HEA,Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ possess two phases,i.e.,FCC and HCP phase.And the RE elements in Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ are only one（Sc）,showing that it may open up a new way for the design of less-RE HCP HEAs.Moreover,the advantage of low density about 2.67 g·cm^-3 indicates the tremendous potential in aeronautics,etc.Because the structural stabilities,thermodynamic and elastic properties of the two phases have not been studied previously,and the study of these properties is conducive to the further development of the materials in theory and application.Therefore,the structural stabilities,thermodynamic and elastic properties of FCC and HCP phase in Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ HEAs have been studies in this paper,the main content is as follows.Firstly,first-principles calculations based on density functional theory as well as the special quasi-random structure（SQS）are used to address the problem of the structural stabilities of FCC and HCP phase in Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ HEAs.Results show that HCP phase has better compressibility resistance due to slightly higher bulk modulus.The study of formation enthalpy shows that Both structures are thermodynamic metastable at 0 K.Debye-Grüneisen model is used to study the thermal properties of the two phases.Results show that the bulk moduli of both phases decline similarly as temperature increases,and bulk modulus of HCP phase is usually larger,while FCC phase possesses lager volumetric thermal expansion coefficient at finite temperature.The research of entropy shows that HCP phase has a larger entropy than FCC.The problem of predicting the structural stability and the thermodynamic properties of the two phases with the change of temperature is solved in the study,providing the theoretical guidance for the design of material composition as well as synthesis and application of the material.Secondly,first-principles calculations based on density functional theory,the special quasi-random structure（SQS）as well as energy-strain method are used to study the elastic properties of FCC and HCP phase in Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ HEAs.The results show that both structures are mechanical stable.The elastic modulus of polycrystalline show that the FCC structure has higher Young’s modulus and shear modulus,so it holds higher stiffness and better resistance to reversible shear deformation.Moreover,both structures are ductile,and the ductility of HCP structure is better.Calculation results of Debye temperature show that the FCC structure has stronger chemical bonds and better thermal conductivity.Finally,the elastic anisotropy of the two materials is studied.The results show that the FCC structure is more anisotropic than the HCP structure.The problem of predicting the mechanical properties of materials is solved in the study,providing the theoretical guidance for the application of the material in mechanics.