Crystal structure, thermodynamics, magnetics and disorder properties of Be–Fe–Al intermetallics

Highlights: • DFT atomistic modelling + phonon DOS + Bragg–Williams order/disorder. • A novel Fe–Be binary structure was identified ε-Fe₂Be₁₇. • Small additions of Al stabilises δ-FeBe₅ over ζ-FeBe₂ and ε-Fe₂Be₁₇. • δ-FeBe₅ and ε-Fe₂Be₁₇ may accommodate deviations from stoichiometry. - Abstract: The elastic and magnetic properties, thermodynamical stability, deviation from stoichiometry and order/disorder transformations of phases that are relevant to Be alloys were investigated using density functional theory simulations coupled with phonon density of states calculations to capture temperature effects. A novel structure and composition were identified for the Be–Fe binary ε phase. In absence of Al, FeBe₅ is predicted to form at equilibrium above ∼1100 K, while the ε phase is stable only below ∼1500 K, and FeBe₂ is stable at all temperatures below melting. Small additions of Al are found to stabilise FeBe₅ over FeBe₂ and ε, while at high Al content, AlFeBe₄ is predicted to form. Deviations from stoichiometric compositions are also considered and found to be important in the case of FeBe₅ and ε. The propensity for disordered vs ordered structures is also important for AlFeBe₄ (which exhibits complete Al–Fe disordered at all temperatures) and FeBe₅ (which exhibits an order–disorder transition at ∼950 K)