First-Principles Study On Cu-Cr-Zr-RE Alloy Compounds

Cu-Cr-Zr-RE alloys are widely used in electronics,electric power,aviation,aerospace,motor manufacturing,welding tools and other fields because of their high strength and high conductivity.The alloy belongs to precipitation strengthening alloy.The precipitates dispersed in the alloy can be precipitated by solid solution aging treatment,which have a great influence on the comprehensive properties of the alloy.The precipitation in Cu-Cr-Zr-RE alloy has a great influence on the comprehensive properties of the alloy.However,due to the limitations of test methods and less alloy elements,the composition and structure of the intermetallic compounds precipitated in the alloy are still divergent,and there is a lack of related property research.In addition,due to the role of rare earth elements(RE)in purifying the matrix and improving the microstructure,many researchers have applied it to Cu-Cr-Zr alloys,but there are few studies on the rare earth compounds that may precipitate in the alloys after RE addition.In this paper,the thermodynamic properties(enthalpy of formation,binding energy,Debye temperature),electronic structure(density of states,energy band structure)and mechanical properties(bulk modulus,shear modulus,Young's modulus,Poisson's modulus)of Cu-Zr,Cu-La,Cu-Y intermetallic compounds in Cu-Cr-Zr-RE(RE=La,y)alloys were calculated and analyzed by CASTEP module of Material Studio based on first principles calculation method.In order to provide theoretical data for the further development of Cu-Cr-Zr alloys.The main results are as follows:1.The seven Cu-Zr compounds(Cu₅Zr,Cu₅₁Zr₁₄,Cu₈Zr₃,Cu₂Zr,Cu₁₀Zr₇,Cu Zr and Cu Zr₂)are thermodynamically stable phases.Among them,the enthalpies of formation of Cu₈Zr₃and Cu₁₀Zr₇are lower,which are-16.57k J·mol^-1and-16.38k J·mol^-1,respectively,and they are easy to form;the binding energy of Cu Zr₂is lower,which is-614.94k J·mol^-1,and it is more stable;the Debye temperature of Cu₅Zr is higher,which is 380K,and the covalent bond strength is relatively higher.The calculated results of density of states show that the bonding bonds of the seven compounds are composed of metal bonds and covalent bonds.Among them,the hybrid degree of 3d orbital electrons of Cu and 4d orbital electrons of Zr in Cu Zr₂is the largest,and the pseudogap of Cu₁₀Zr₇is the widest,which further proves its stability.The band structure indicates that Cu₅Zr,Cu₅₁Zr₁₄,Cu₈Zr₃,Cu₁₀Zr₇,Cu Zr and Cu Zr₂are conductors,while Cu₂Zr may be semiconductor with a band gap of 0.024e V.Except Cu₅₁Zr₁₄,the other six compounds are all mechanical stable phases.Among them,Cu₈Zr₃has stronger resistance to deformation under external pressure with bulk modulus of 130GPa;Cu₅Zr has higher hardness and poor ductility,Cu Zr has lower hardness and greater ductility.2.The six Cu-La compounds(?Cu₆La,?Cu₆La,Cu₅La,Cu₄La,Cu₂La and Cu La)are thermodynamically stable.Among them,the stability of Cu La is relatively good,which is attributed to its lower formation enthalpy(-11.58k J·mol^-1),lower binding energy(-424.95k J·mol^-1),high hybrid degree of 3d and 4s orbital electrons of Cu and 5d orbital electrons of La,and he widest pseudo energy gap.The binding bonds of the six compounds are all composed of metal bonds and covalent bonds,showing the properties of conductor,and they are all mechanical stable phases.Among them,?Cu₆La has stronger resistance to deformation caused by external force,and its bulk modulus is 96GPa;Cu₅La has higher hardness and brittleness;Cu La has lower hardness and better ductility.3.The three Cu-Y compounds(Cu₅Y,Cu₂Y and Cu Y)are thermodynamically stable.Among them,Cu₂Y has the lowest enthalpy of formation(-20.38k J·mol^-1)and larger pseudo energy gap in the density of states,and has a better stability;Cu Y has the lowest binding energy(427.28k J·mol^-1),the highest Debye temperature(325K)and the higher hybrid degree of 3d orbital electrons of Cu and 4d,4p and 5s orbital electrons of Y,and also has a better stability.The binding bonds of the three compounds are all composed of metal bonds and covalent bonds,showing the properties of conductor,and they are all mechanical stable phases.Among them,Cu₅Y has stronger resistance to external forces,and higher hardness;Cu₂Y has lower hardness and higher ductility.4.Comprehensive comparison of the intermetallic compounds of the Cu-Zr,Cu-La,Cu-Y systems shows that Cu-Zr intermetallic compounds have better structural stability,higher covalent bond strength,stronger resistance to external forces,higher average valence bond strength and higher hardness,and they are easier to exist in Cu-Cr-Zr-RE(RE=La,Y)alloys.