First-principle Study Of Fracture Properties Of Cr₂Nb

The new high-temperature structural material Laves phase intermetallic compound Cr2Nb has many excellent potential properties,but the Laves phase intermetallic compound has high brittleness at room temperature,which greatly limits its practical application range.In this paper,the first principles calculation method based on density functional theory is used to study the three structures of C15,C14 and C36 of Laves phase intermetallic compound Cr₂Nb,and calculate the M element atoms occupies the position and the electronic structure and its mechanical properties after the element M?M=Ti,W,Mo,V,Zr?is doped into the C15-Cr2Nb system.Finally,the fracture properties of the C15-Cr2Nb doping system along the three crystal planes of?1 0 0?,?1 1 0?and?1 1 1?were studied and analyzed,and the microscopic fracture mechanism of the Laves phase intermetallic compound Cr2Nb was explored and revealed,and provides a theoretical basis for improving the room temperature brittleness of Cr-Nb alloy.Firstly,by using the first principles method based on the density functional theory,the electronic structures such as the formation enthalpy,binding energy and density of state of the three cell structure systems C15,C14 and C36 of the Laves phase intermetallic compound Cr₂Nb were studied.The mechanical properties such as elastic constant,elastic modulus and Poisson's ratio are all consistent with the experimental values.The results show that the C15structure has the strongest alloying ability and its phase stability is also high.Among them,C14 is the highest brittleness at room temperature,while the C36 structure is the lowest brittleness at room temperature.Then,the lattice occupancy of the doped alloying elements M?M=Ti,W,Mo,V,Zr?in the C15-Cr₂Nb unit cell were calculated,and the density of states of the doped system were also calculated.And according to the occupancy situation,the structural parameters and mechanical properties of the C15-Cr₂Nb doping system with different atomic percentages of M atoms were calculated.Based on the calculated results,Ti and Zr tend to occupy the lattice position of Nb atoms in C15-Cr₂Nb,while W,Mo and V atoms tend to occupy the lattice position of Cr atoms,of which V atoms'tendency is strong,and W And Mo atoms'tendency are weaker.The calculation of the density of states shows that W,V,Zr elements increases the hybrid effect between Nb atoms and Cr atoms,which may be helpful to reduce the brittleness at room temperature of C15-Cr₂Nb.After doping Zr element,the deformation ability and phase stability of the doped system increased with the increase of concentration,while the downward trend of brittleness shows that the Zr element could be the most helpful to improve system's brittleness.Finally,by calculating the fracture energy Gc and the critical stress?of the doping system along the three crystal planes of?1 0 0?,?1 1 0?and?1 1 1?,the fracture properties were studied.The results show that the doping elements W and V occupy the lattice position of the Cr atom and the doping element Zr occupy the lattice position of the Nb atom,which can improve the fracture properties of the C15-Cr2Nb doped system.W is effective,while it is not ideal to improve the fracture properties of the doping system.The doping element Mo occupies the lattice position of the Cr atom,and Ti occupies the lattice position of the Nb atom,which reduce the fracture strength of the doping system C15-Cr₂Nb.These results are also consistent with the experimental results.By calculating the differential charge density,the charge density map of the doped system<110>surface is obtained.The influence mechanism of doping elements on the fracture properties of C15-Cr₂Nb system was revealed at the microscopic level,indicating that the strong hybridization between doping element M and the system atom is the key to improve the fracture properties of the Cr-Nb alloy system.