A First-principles Study Of Ni-Al Intermetallic Compounds

In this paper,based on density functional theory,five Ni-Al intermetallic compounds,NiAl,Ni₃Al,NiAl₃,Ni2Al₃,Ni5Al₃ are theoretically studied.Specific analysis of Ni-Al intermetallic compound formation enthalpy,electronic structure and population,elastic modulus and elastic anisotropy;electronic structure under high pressure,mechanical properties,thermodynamic properties;and rare earth element RE（RE=Sc,Y,La,Ce,Pr,Nd,Pm,Sm,Eu,Ho,Er,Tm,Yb,Lu）on Ni₃Al.The specific research results are as follows:Formation enthalpy studies show that NiAl is the most stable among the five Ni-Al intermetallic compounds under normal pressure.The contribution of the density of states of the five Ni-Al intermetallic compounds near the Fermi level mainly comes from the 3d orbitals of Ni atoms and the 3p orbitals of Al atoms,and p-d hybridization is formed between Ni atoms and Al atoms.The electron transfer situation shows that Ni atoms get electrons,and Al atoms lose electrons.The mechanical stability conditions are all stable.According to the analysis of polycrystalline elastic modulus and B/G value,Ni₃Al has the largest bulk modulus,and Poisson’s ratio v and B/G value are the best toughness.NiAl has the highest shear modulus and Young’s modulus;The order of the overall anisotropy in the anisotropy index AU analysis is:Ni₃Al>Ni5Al₃>NiAl>NiAl₃>Ni2Al₃.Under high pressure,the bulk modulus B,shear modulus G,Young’s modulus E,B/G value,and Poisson’s ratio v of five different Ni-Al intermetallic compounds increase continuously with the increase of pressure.The anisotropy of the five Ni-Al intermetallic compounds keeps increasing with increasing pressure.The coefficient of thermal expansion increases with the increase of temperature and decreases with the increase of pressure.The Debye temperature（θD）decreases slightly with the increase of temperature,and gradually increases with the increase of pressure.When the temperature reaches the Debye temperature,the isobaric heat capacity Cv conforms to the Dulong-Petit law,that is,as the temperature continues to increase,Cv gradually becomes a constant independent of temperature,while the isobaric heat capacity continues increase.According to the doping formation energy and occupancy tendency energy AEsite,it shows that Eu,Er,Tm,Yb tend to occupy Ni sites,while Sc,Y,La,Ce,Pr,Nd,Pm,Sm,Ho,Lu tend to occupy Al Position;the ternary compound of the doping system is metallic.There are mainly RE-Al and Ni-Al covalent bonds in the doping system.The bulk modulus B,shear modulus G,and Young’s modulus E of different doping systems all have different degrees of reduction.Except for Ni24Al7Y Ni24Al7Er and Ni24Al7Tm,the toughness of the doped system is basically improved.Among them,the best improved toughness is Ni23Al8Sm.The anisotropy of the same element occupying Ni sites is greater than the anisotropy of occupying Al sites.