The elastic properties of disordered Fe-Ni alloys under high pressures from first-principles calculations

The elastic constants and the elastic anisotropy in hexagonal close-packed Fe-Ni alloys have been investigated at high pressures by plane-wave density functional calculations within the generalized gradient approximation and the Monte Carlo special quasi-random structure method. The comparisons with previous calculations and experiments are shown and discussed. We find that adding Ni to Fe has a certain influence on the structure and elasticity of hexagonal close-packed Fe-Ni alloys generally. In particular, the elastic constant C-44 is seriously affected by the increasing Ni content. Furthermore, the elastic moduli and wave velocities yielded from disordered structures are slightly greater than those from the ordered structures in previous calculations at high pressures. Interestingly, the elastic anisotropies of the compressional wave are close to 1.1 and there are small changes with increasing pressure and Ni content, which indicates that the anisotropies are little affected by pressures and Ni content within disordered structure.