First-principles Study Of Electronic Structure Properties And Mechanical Behaviors In Nickel-based Superalloys

Nickel-based single-crystal superalloys are used extensively for blade applications in advanced aircraft engines because of their superior mechanical properties in high-temperature ranges.These excellent elevated temperature properties are closely related to theirγ′volume fraction and alloying additions.The present work is aimed at per-forming first-principles calculations to systematically investigate theγ′-volume-fraction dependence of elastic performance and the partitioning behaviors and site preferences of transition-metal elements as well as their effects on the elastic and electronic properties of nickel-based terary model superalloys,hoping to provide reference data for further re-search into the elastic properties and a new perspective of the mechanical characteristics and composition design of nickel-based model superalloys.First-principles calculations are carried out to investigate the structural,elastic,and electronic properties of nickel-based model superalloys.The effects of alloying element X（where X=Hf,Ta,Mo,W,Cr,Re,Ru,or Co）on the mechanical characteristics of Ni/Ni₃Al ternary multilayer structures are obtained and discussed.Theγ′-volume-fraction dependence of mechanical performance is studied in detail for the first time.The influence of alloying elements on bulk modulus is almost independent ofγ′volume frac-tion.While the effects of alloying elements on shear modulus,Young’s modulus,the duc-tile and brittle behavior,some particular orientation-dependent elastic moduli and Zener anisotropy factor are closely related toγ′volume fraction.Among the threeγ′volume fractions investigated in this work,nickel-based ternary model superalloys with 60%γ′volume fraction have significant improvement in Young’s and shear moduli and thus pos-sess the best comprehensive elastic performance.Furthermore,alloying dopants and Ni atoms from the interface and two phases share a DOS peak just below the Fermi level,and this additional d-d hybridization leads to the exceptional mechanical performance of superalloys with 60%γ′volume fraction.Alloying effects on the structural,elastic,as well as electronic properties of nickel-based model superalloys are systematically investigated by first-principles calculations.Twenty-seven transition-metal（TM）elements（3d:Sc-Zn,4d:Y-Cd,5d:Hf-Au）are taken into account in nickel-based ternary model superalloys in detail for the first time.The partitioning behaviors and site preferences of ternary alloying elements are primarily pre-dicted based on our calculated substitutional formation energies and partitioning coeffi-cients,with previous atom probe tomography（APT）experimental results for comparison.Temperature dependence of partitioning behaviors of TM elements in model superalloys is also presented in this work.It is found that the partitioning behaviors of Cr,Mn,Tc,Ru and Os can be reversed at a specific temperature,and these elements just lie near the boundary between the two blocks of Ni-site preferences and Al-site preferences of TM elements on the periodic table.The bulk moduli,Young’s moduli,shear moduli,ductile-brittle behavior,orientation-dependent elastic moduli and elastic anisotropy of nickel-based ternary model superalloys are systematically estimated.The calculated elastic pa-rameters agree well with the available experimental results.The effects of TM elements on elastic properties are found to be closely associated with their d-electron number.The elements at the beginnings and ends of the TM series reduce these elastic properties,while the TM elements lying towards the center of each period can considerably increase these properties of superalloys,especially those elements with a half-filled d band,which exert greater influences on improving the elastic performance.Furthermore,different charge redistributions caused by each alloying addition can elucidate different effects thereof on the elastic properties of model superalloys to some extent.The stronger directional bond-ing and more covalent-like interaction between TM additions and host atoms lead to the superior elastic properties.