First-principles based thermodynamic model of phase equilibria in bcc Fe-Cr alloys

A first-principles based thermodynamic model for magnetic alloys is applied to the calculation of the Fe-Cr phase diagram restricted by the bcc structure. The model includes magnetic, electronic, phonon, and local atomic relaxations contributions to the free-energy derived from ab initio calculations. Atomic short-range-order effects are found to be relatively small and they have been neglected in the calculations, assuming that alloys are in the completely random state. In contrast, we have taken into consideration magnetic short-range-order effects, which are found to be very important in particular above the Curie temperature. The calculated phase diagram is in reasonable agreement with the latest CALPHAD assessment. Our calculations reproduce a feature known as a Nishizawa horn for the Fe-rich high-temperature part of the phase diagram.