Experimental investigation of the Al–Co–Fe phase diagram over the whole composition range

Abstract

Knowledge of the phase stability in the Al–Co–Fe ternary system is critical for developing Al–Fe–Si-based low-cost lightweight high-temperature materials and is thus experimentally investigated over the whole composition range. Three complete isothermal sections at 1000, 900, and 800 °C were constructed based on the results measured from three identical Co/Fe/Al5Fe2 diffusion triples and forty-three equilibrated alloys using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). At all the three temperatures, a continuous solution, Al13(Co,Fe)4, was confirmed between the Al13Fe4 and M-Al13Co4 phases. Phase boundaries of the γ, α, β, Al2Fe, Al5Fe2, Al5Co2, Al9Co2, and Al13(Co,Fe)4 phases and the corresponding phase equilibrium relations were clearly defined from the obtained tie-lines and phase boundary data. Three three-phase regions were confirmed in the 1000 °C isothermal section, while four three-phase regions were confirmed in the 900 and 800 °C isothermal sections. The large amount of new phase equilibrium data proposed in this work will serve as reliable input for future thermodynamic reassessments of the Al–Co–Fe system within the CALPHAD (CALculation of PHAse Diagrams) framework to improve the current Al thermodynamic databases.