Experimental and computed phase diagrams of the Fe–Re system.

In order to clarify controversial reports on the Fe-Re phase diagram, a new experimental investigation has been carried out. Three intermetallic phases have been evidenced, including the new report of the P phase found for the first time in a binary system. The phase relations involving the σ phase were established. In parallel, a first-principles study has been performed which provided the heat of formation of every ordered configuration for four intermetallic phases (D8(b), A12, A13 and P). The mixing energy of solid solutions (fcc, bcc, hcp) was calculated using the special quasi-random structure method. Calculations were performed with the help of the density functional theory, with and without spin polarization. From these results, in the frame of the Compound Energy Formalism using the Bragg-Williams approximation, the Fe-Re phase diagram has been computed without the use of adjustable parameters. Different thermodynamic parameters obtained experimentally and theoretically, as the site occupancies, are compared. The computed phase diagram presents several differences with the experimental one. To understand these differences, the influence of several parameters on the phase stability, such as the magnetic contribution has been evaluated.