Effects of pressure on lattice parameters, electronic, thermodynamic and mechanical properties of the fully ordered Ti_(2)AlNb orthorhombic phase were studied using first-principles calculations based on density functional theory(DFT). The bonding nature for ordering orthorhombic Ti_(2)AlNb was revealed quantitatively through the electronic structure analyzing. The external pressures play limited roles in the elastic anisotropy of the alloy due to the outstanding dynamical and mechanical stabilities under pressure. However, the shear modulus of O phase manifests anisotropic, where {010} shear planes are the easiest planes to cleave among the principal planes under all pressures.The heat capacities, volume expansions and thermal expansion coefficients were calculated using the quasi-harmonic approximation model based on the phonon dispersion curves. Meanwhile, the bulk modulus, Young’s modulus,shear modulus and the hardness are promptly enhanced under pressure. The predicted results give hints to design Ti_(2)AlNb-based alloy as high-pressure applications.
The multi-principal high-entropy alloys (HEAs) are promising new alloys.However,it is a challenge to screen out the suitable composition from the diverse combinations.Referring to the prototype AuCu 3 with AB 3-L1 2 structure,where it becomes a face-centered cubic (fcc) structure if element A and B are the same element,the site occupying tendencies of the elements and thermodynamic functions are predicted by using the sublattice model supported with first-principles total energy calculations.By considering the Gibbs energy of formation and the configurational entropy,the fcc HEAs in available literatures are examined,and the results of the quinary system with equal-atomic composition CoFeMnNiM and the hexbasic system with equal-atomic composition CoFeMnNiSmM are reported,respectively,where the element M is selected from the rest of the periodical table.When M=Cr,Zn,Ru,Rh,Pd,Re,Os,Ir,or Pt in the quinary systems CoFeMnNiM and when M=Ru,Pd,or Pt in the hexbasic systems CoFeMnNiSmM,respectively,the alloys are recommended to be potential fcc HEAs.The new approach opens a new way to mine the rich ores of HEAs.
