Structural, energetic and dynamical properties of ordered and disordered bcc Fe25at.%Ni alloys: A first-principles study

Abstract

Using first-principles phonon calculations and the Quasi-Harmonic approach, the structural, energetic and dynamical properties of ordered (D03) and disordered Fe25at.%Ni bcc alloys have been investigated. All calculations are based on the Projector Augmented Wave (PAW) method of the Density Functional Theory (DFT). The Special Quasirandom Structure (SQS) method has been used to model the disordered structure. It is found that 25at.% Nickel substitution increases the lattice parameter and consequently decreases the C11 and C12 elastic constants and bulk modulus of bcc-iron. Simultaneously, the C44 elastic constant increases with Ni substitution. The calculated formation energies of the disordered structures at 0K are lower than those of the ordered one. The predicted phonon spectra reveal the dynamical stability of both SQS and D03 structures. Finally, the Gibbs free energy functions indicate that the relative stability of the disordered structure vs the ordered one increases with increasing temperature.