Research Progress in Composition Design and Mechanical Properties of Eutectic High Entropy Alloys
Eutectic high entropy alloys were a novel type of multi-principal alloy developed in recent years.As compared with single-phase high entropy alloys,eutectic high entropy alloys were composed of both soft and hard phases.Eutectic high entropy alloys demonstrated high comprehensive mechanical properties and excellent castability,making them a promising material for a variety of industrial applications.Several studies indicated that the microstructure of eutectic high entropy alloys undergone a transformation from hypoeutectic to eutectic and hypereutectic,depending on the content of key alloying elements.Therefore,efficiently studied the composition of eutectic points in the high entropy alloy system was crucial for predicting their existence and developing innovative types of eutectic high entropy alloys.That paper provided a review of four distinct approaches for designing the composition of eutectic high entropy alloys.The first method used to determine the eutectic point of eutectic high entropy alloys was the trial-and-error method.Those altering the content of 1 to 2 key alloying elements.The second method employed was the simple mixing method,which utilized the binary phase diagram and enthalpy of element mixing.The third method utilized thermodynamic calculation.For example,the pseudo-binary phase diagram of CoCrFeNiNb,high entropy alloys was calculated by using Themo-Calc software and the Ni-based alloy thermodynamic database.Co,Cr,Fe and Ni elements were treated as a single element in the pseudo-binary alloy,while Nb element was treated as another single element.The fourth method was the mixed enthalpy method,based on composition of existed eutectic high entropy alloys,a new eutectic high entropy alloys composition was designed by using the mixing enthalpy method.Meanwhile,this review provided a summary of the phase composition and mechanical properties of typical eutectic high entropy alloys.It was found that the majority of eutectic high entropy alloys were composed of face center cubic(fcc)and intermetallic compound(IMC)dual phases(such as Laves phase,μ phase,B2 phase and carbide),and a small number of eutectic high entropy alloys were composed of body center cubic(bcc)and ordered bcc(B2)dual-phases.Moreover,this study provided a summary of the compression and tensile properties of eutectic high entropy alloys at both room and high temperatures.Additionally,the main influencing factors of compressive and tensile strength of these alloys were also discussed,and it was revealed that eutectic high entropy alloys exhibited a compressive strength higher than 1.8 GPa.Those was attributed to the microstructure characteristics of dual phase(high strength phases and high plastic phases)of eutectic high entropy alloys.The fracture strain of fcc+B2 type eutectic high-entropy alloys was found to be higher than that of fcc+IMC type eutectic high-entropy alloys,which was caused by plasticity of B2 phase was superior to that of IMC phase,with topologically close-packed structure.The room temperature compressive strength of AlCoCr0.5FeNi2.1 and AlCoCr0.25FeNi2.1 alloys was significantly higher than that of AlCoCrFeNi2.1 and AlCoCr0.2FeNi2.8 alloys.Those was attributed to the higher area fraction of B2 phases in AlCoCr0.25FeNi2.1 and AlCoCr0.5FeNi2.1 alloys.In summary,the compressive strength of eutectic high entropy alloys at room temperature was influenced by the crystal structure of the phases and the area fraction of high strength phases.In addition,it was found that the high temperature compressive strengths of fcc+Laves type eutectic high entropy alloys were higher than that of fcc+B2 type eutectic high entropy alloys.The interdiffusion coefficient of high refractory elements(Nb and Hf)in γ-Ni was significantly lower than that of Al in γ-Ni.Therefore,the high temperature compressive strength of eutectic high entropy alloys was influenced by multiple factors,including the crystal structure of high strength phases,interdiffusion coefficient of elements and the content of high refractory elements.Moreover,CoFeNi2V0.5C0.2 alloy exhibited high tensile plasticity and low tensile strength,which was due to its divorced eutectic structure of fcc+carbide,that was,this microstructure resulted in a point distribution of carbide phases.Therefore,CoFeNi2V0.5C0.2 alloy displayed similar tensile properties to that of fcc phase with high plasticity and low strength.In addition,Ni30Co30Cr10Fe10Al18W2 eutectic high entropy alloys showed higher tensile strength,which was attributed to higher area fraction of flat eutectic phases and the solid solution strengthening of W atom.As a result,the tensile strength of eutectic high entropy alloys at room temperature was dependent on both the morphology of eutectic phases and the solid solution strengthening impact of the alloying elements.
eutectic high entropy alloyscomposition designroom temperature compression propertieshigh temperature compression propertiesroom temperature tensile properties
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