Ab initio phase stability of some cubic phases of ordered Ni-Fe alloys at high temperatures and pressures

• A method developed from self-consistent ab initio lattice dynamics (SCAILD) is used to calculate the free energy of different structures.
• The anharmonic part of free energy plays an important role in stabilizing the fcc-Ni3Fe structure at high temperatures and pressures.
• The dynamically stable regions of Ni3Fe compound are predicted in the phase diagram, and bcc-Ni3Fe phase is expected to be stable at high temperature and pressure.

To address the temperature-induced stabilization of different phases, we studied some special structures of ordered Ni-Fe alloys by applying the recently developed self-consistent ab initio lattice dynamics approach. A simple but efficient scheme was also used to calculate the free energy and entropy. We found that the ordered structures with high nickel content are easier to stabilize at high temperature. Especially, the anharmonic part of free energy plays an important role in stabilizing the fcc-Ni3Fe structure at high temperatures and pressures. Finally, the dynamically stable regions of Ni3Fe compound are predicted in the phase diagram, and bcc-Ni3Fe phase is expected to be stable at high temperature and pressure.

Graphical AbstractIt is usually difficult to obtain an accurate estimation of free energy duo to the effect of anharmonic part at finite temperature. The temperature-induced stabilization of materials are also difficult to be determined under high temperatures and high pressures owing to the anharmonic phenomenon. In this work, to consider the temperature-induced stabilization of face-centred cubic phase of binary Fe-Ni alloys, we study some ordered Ni-Fe alloys with special structures by applying the recently developed self-consistent ab initio lattice dynamics approach. A simple but accurate scheme is also used here to calculate the free energy and corresponding entropy. Our results show that phonon-phonon interaction plays an important role in stabilizing the face-centred cubic phase at high temperatures and pressures. Finally, the dynamically stable regions of Ni3Fe compound are predicted in the phase diagram, and bcc-Ni3Fe phase is expected to be stable at high temperature and pressure.Figure optionsDownload as PowerPoint slide