First-principles modeling of energetic and mechanical properties of Ni-Cr, Ni-Re and Cr-Re random alloys

We apply the exact-muffin-tin-orbitals (EMTO) method to investigate structural properties, formation enthalpies, mechanical stability and polycrystalline moduli in Ni-Re, Ni-Cr and Cr-Re disordered fcc, bcc and hcp phases. Substitutional disorder is treated by using the coherent potential approximation (CPA). We predict the alloy lattice parameters in good agreement with the experiment. We find a continuous softening, as a function of Cr composition, of the tetragonal shear modulus C′ in fcc Ni-Cr phase indicating mechanical instability in Cr-rich Ni-Cr alloys. On the other hand, we show that the mechanical stability of fcc Ni-Re alloys persists through the whole composition range. We observe an intriguing behaviour of the Young's modulus vs. the intrinsic ductility curve in Ni-rich Ni-Re fcc phase.