First Principle Study Of Elements Doping And Plastic Deformation Mechanism Of Laves Phase TaCr₂

Laves phase TaCr₂ is a potential new type of high temperature structural material,However,Laves phase TaCr₂ usually emerged the serious room temperature brittleness,which greatly hinders its application.In this paper,the lattice structure of Laves phase TaCr₂ under C14,C15 and C36 geometries is proposed by using plane wave pseudopotential method of first-principles density functional theory and the phase stability,electronic structure and mechanical properties of the ternary phase of M?M=Zr,W,Ru,V,Nb?alloys at different concentrations of atomic percent were studied in C15-TaCr₂,and the theoretical tensile properties of C15-TaCr₂ in <001>,<110> and<111> directions were studied,the theoretical shear strength analysis in C15-TaCr₂ of the {111}<112> direction.Thus further revealing the plastic deformation mechanism of Laves phase TaCr₂ compounds.And provide the theoretical basis for the improvement of room temperature brittleness of TaCr₂ alloy and the design of new Ta-Cr superalloy.Firstly,the Laves phase TaCr₂ of C14,C15 and C36 structures were optimized by the first principle method,and the electronic structure and mechanical properties of the three structures were calculated.The equilibrium lattice constants of the calculated C15,C14 and C36 structures are in good agreement with the experimental values.The calculated enthalpy and binding energy and electronic structure analysis show that the C15 structure alloying ability is the strongest and the phase stability is:C36<C14<C15.The valence electrons of the three structures are in the reverse bond state,and are mainly in the bond state.Then,the lattice space pattern of C15-TaCr₂ added with the transition metal element M?M=Zr,W,Ru,V,Nb?was calculated.According to the occupancy situation,the different atomic percentage concentration of M elements to C15-TaCr₂ to calculate the lattice structure and mechanical properties.Analysis of lattice occupancy energy shows that Zr and Nb tend to preferentially occupy the lattice position of Ta atoms in Laves phase C15-TaCr₂,while W,Ru and V tend to occupy the lattice position of the Cr atom.By analyzing the Fermi energy values of the ternary phase Fermi energy level after doping 4.17% atomic percentage concentration of M element,the size of the phase stability is:Ta7ZrCr16<Ta8Cr15Ru<Ta8Cr15V<Ta8Cr16<Ta7NbCr16<Ta8Cr15W.The results show that the addition of the elements W and Nb makes it harder to becompressed and deformed by C15-TaCr₂,while the addition of Zr,Ru and V elements makes it easier to be compressed and deformed by C15-TaCr₂.The addition of alloying Zr,W,Ru,V and Nb elements can improve the toughness and reduce the brittleness of C15-TaCr₂,Adding a small amount of these alloys may have little effect on hardness.When Zr,W and V elements are doped,the anisotropy of C15-TaCr₂ becomes smaller.Calculating the mechanical properties of the ternary phase with different atomic percentage concentrations to improve the brittleness of C15-TaCr₂.The best is W element,and the additive concentration is between 12.5%²0.83%.Finally,the phase transition of Laves phase TaCr₂ compound under pressure was calculated and the ideal tensile strength of TaCr₂ with C15 along <001>,<110> and<111> tensile directions and the ideal shear strength along {111}<112> tensile directions are calculated.The results show that the brittleness of the applied pressures C14,C15 and C36-TaCr₂ decreases gradually.From the calculated pressure of 0¹50GPa,the first phase transition pressure of C15 transition C14 structure is about 10 GPa,and the second phase transition pressure of C14 to C36 is about 105 GPa.The ideal tensile strength of C15-TaCr₂ along <001>,<110> and <111> tensile directions is about 35 GPa,36GPa and 38 GPa,and the failure strain is 13.47%,19.31% and 16.95%,respectively.The ideal shear strength along {111}<112> tensile directions is about 36 GPa and the strain is about 41.3%.The results shows that the ideal shear strength along{111}<112> tensile directions is higher than that the ideal tensile strength along<001> tensile directions,which leads to the brittle fracture of the C15-TaCr₂ along<001> tensile directions.