Ground-state properties and lattice-vibration effects of disordered Fe-Ni systems for phase stability predictions

Kangming Li (1) , Chu Chun Fu (1)

1 SRMP - Service de recherches de métallurgie physique

By means of density functional theory (DFT), we perform a focused study of both body-centered-cubic (bcc) and face-centered-cubic (fcc) Fe-Ni random solid solutions, represented by special quasi-random structures. The whole concentration range and various magnetic configurations are considered. Excellent agreement on the concentration dependence of magnetization is found between our results and experimental data, except in the Invar region. Some locally antiferromagnetic fcc structures are proposed to approach experimental values of magnetization. Vibrational entropies of ordered and disordered systems are calculated for various concentrations, showing an overall good agreement with available experimental data. The vibrational entropy systematically contributes to stabilize disordered rather than ordered structures, and is not negligible compared to the configurational entropy. Free energy of mixing is estimated by including the vibrational and ideal configurational entropies. From them, low- and intermediate-temperature Fe-Ni phase diagrams are constructed, showing a better agreement with experimental data than a recent CALPHAD prediction for some phase boundaries below 700 K. The determined order-disorder transition temperatures for the L1$_0$ and L1$_2$ phases are in good agreement with the experimental values, suggesting an important contribution of vibrational entropy.

Domains: Materials Science [cond-mat.mtrl-sci]

Kangming Li, Chu Chun Fu. Ground-state properties and lattice-vibration effects of disordered Fe-Ni systems for phase stability predictions. Physical Review Materials, 2020, 4, pp.023606. ⟨10.1103/PhysRevMaterials.4.023606⟩. ⟨cea-02495972⟩