Single-crystal elastic constants of ferromagnetic bcc Fe-based random alloys from first-principles theory

The elastic properties of ferromagnetic Fe_1-x M_x (M=Al, Si, V, Cr, Mn, Co, Ni, and Rh; 0≤x≤0.1) random alloys in the body-centered-cubic (bcc) crystallographic phase have been studied using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The theoretical lattice parameters and the single-crystal elastic constants agree well with the available experimental data. The most significant alloying effects are found for Al, Si, and Ni additions. All elements enlarge the lattice parameter and decrease the C ₁₁, C₁₂, and C^′ elastic constants and the bulk modulus of bcc Fe. At the same time, C₄₄ is found to increase with Al, Si, V, Cr, or Mn and remain nearly constant with Co, Ni, and Rh. Accordingly, the elastic anisotropy of bcc Fe increases with all alloying elements considered here. The calculated alloying effects on the single-crystal elastic constants are shown to originate from volume effects in combination with the peculiar electronic structure of bcc Fe.