Prediction Of Cluster Expansion Structure And Physical Properties Of Inconel 718 Alloy

Inconel 718 superalloy has the advantages of high-temperature oxidation resistance and good corrosion resistance compared with ordinary alloys,so it is widely used in components such as aero engines,turbine disks,working blades of turbine parts of gas turbine hot-end components,guiding heat slices and combustion chambers.At present,there have been a large number of reports about Inconel 718 alloy in terms of theoretical calculations.However,little has been reported about the formation energy,phonon spectrum,first-principles molecular dynamics and thermodynamic properties of theγ"-Ni_3-xNb_x（0≤x≤1）alloy and-Ni₃Al_1-xV_x（0≤x≤1）system.In order to further expand the data of Inconel 718 high-temperature alloys,a combination of cluster expansion method and first-principles approach is used in this paper to study bothγ"-Ni_3-xNb_x（0≤x≤1）and-Ni₃Al_1-xV_x（0≤x≤1）systems.The main conclusions are as follows.The formation energy ofγ"-Ni_3-xNb_x（0≤x≤1）alloys at different Nb concentrations is calculated using a combination of cluster expansion method and first-nature principle,while a convex packet diagram of the formation energy of the binary alloy system is constructed,and finally eleven ground state structures are predicted for the whole range of 0≤x≤1.The dynamic and mechanical stability of these predictedγ"-Ni_3-xNb_x ground state structures is further demonstrated by studying their phonon spectra,first-principles molecular dynamics and elastic constants.It is shown that the Ni₈,Nb₈,Ni₄Nb₁₂,Ni₆Nb₂,Ni₁₄Nb₂,Ni₁₃Nb₃,and Ni₁₂Nb₄phases are dynamically stable.By studying the stable ground state structures,it was found that temperature has a large effect on the thermodynamic properties of the systems.The elastic properties were studied and Ni₆Nb₂ was found to have the largest Young’s modulus E,indicating that Ni₆Nb₂ has the strongest stiffness.Also by studying B/G andυ,it is found that these ground state structures are ductile.In addition,the density of states of Ni₆Nb₂,Ni₁₄Nb₂,Ni₁₃Nb₃ and Ni₁₂Nb₄systems were found to be located at the peaks and valleys,indicating that the system has metallic characteristics and electrical conductivity.The formation energy of theγ’-Ni₃Al_1-xV_x（0≤x≤1）system was calculated by a combination of cluster expansion method and first-nature principle,and nine ground state structures in the whole range of 0≤x≤1 were predicted at the same time.The phonon spectra and first-principles molecular dynamics studies revealed that the Al Ni₆V,Al₂Ni₁₈V₄,Al₃Ni₁₂V,Al₃Ni₁₅V₂,Al₂Ni₁₅V₃,Al Ni₁₂V₃,and Al₄Ni₁₈V₂ phases are kinetically stable,with the Al₂Ni₁₈V₄and Al Ni₁₈V₅ ground state structures showing soft modes,indicating their kinetic instability.Thermodynamic calculations show that temperature and pressure have a large effect on the system.By studying the elastic properties it was found that Al₂Ni₁₅V₃ exhibited the best toughness characteristics when the V atom concentration was 0.6.The calculation of the density of states shows that the system has metallic characteristics.In addition,the study of the local charge density reveals the presence of metallic and covalent bonds in the system,and the presence of covalent bonds can improve the strength of the alloy.