New experimental studies on the phase diagram of the Al-Cu-Fe quasicrystal-forming system

Phase diagrams of quasicrystal-forming alloy systems, such as Al-Cu-Fe, are essential to the continued development and fundamental understanding of quasicrystalline alloys, especially for the synthesis of single quasicrystals. Isothermal sections of the Al-Cu-Fe system at 700, 800, and 1000 °C were constructed over the whole composition range by investigations of three Cu/Fe/Al5Fe2 diffusion triples and forty-seven equilibrated alloys using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). Based on experimental measurements and reasonable assumptions, eleven, eight, and six three-phase equilibria were obtained at 700, 800, and 1000 °C, respectively. The existence of the ternary I-Al6Cu2Fe icosahedral quasicrystalline phase was confirmed at both 700 and 800 °C, and the ternary ω-Al7Cu2Fe phase was only found at 700 °C. The stable composition range of the I phase was measured to be Al67-56Cu24-31Fe9–13 and Al66-58Cu23-28Fe11–14 at 700 and 800 °C, respectively. A wide continuous solution region formed among the α-Fe, β-AlFe, and Cu3Al phases at 800 and 1000 °C. A sufficiently large amount of new experimental phase equilibrium data was collected for the Al-Cu-Fe system that will help improve future thermodynamic description of this ternary system within the CALPHAD (CALculation of PHAse Diagrams) framework for designing Al-Cu-Fe-based quasicrystals.