Elastic properties of Cu-Ni and Cu-Zn alloys based on first-principles calculations

The compositional dependence of the elastic properties of Cu-Ni and Cu-Zn solid-solution alloys was investigated using first-principles calculations based on the special quasi-random structure approach. The bulk moduli were found to be largely insensitive to the shape of the electronic density of states (DOS) over the entire composition range. In contrast, when the flat shape of the DOS near the Fermi level was not accurately reproduced, oscillations reflecting the shape of the DOS near the Fermi level were observed in the compositional trends of the Young's and shear moduli at solute concentrations of approximately 40 at.% or lower. When the flat characteristics of the 4 s - and 4 p -orbital DOS were properly reproduced, linear dependence of the elastic properties on the composition was confirmed for both Cu-Ni and Cu-Zn alloys. For Cu-Ni alloys with Ni contents of 60 at.% or higher, the increases in Young's and shear moduli became steeper owing to the influence of spin polarization. These findings highlight the importance of accurately reproducing the flat 4 s - and 4 p -orbital DOS to reliably predict the Young's and shear moduli in Cu-based solid-solution alloys, where the DOS near the Fermi level is predominantly composed of 4 s and 4 p orbitals.