Thermodynamics and phase equilibria of the Al–Fe–Gd metallic glass-forming system

Owing to its importance as a metallic glass-forming system, the ternary Al–Fe–Gd system in its Al-rich corner was examined experimentally to assist in a thermodynamic assessment of this system. X-ray diffraction and TEM–EDS results from annealed specimens confirmed the solid-state equilibria reported previously. Differential thermal analysis of 24 alloys yielded critical temperatures pertaining to the solid–liquid equilibria. A self-consistent thermodynamic database for the Al–Fe–Gd system was developed using the CALPHAD approach. Parameters describing the Gibbs free energy of various phases of the Al–Gd and Al–Fe–Gd systems were manually optimized in this study. Phase equilibria calculations carried out with these parameters showed good agreement with DTA data from this and other studies, as well as thermochemical data reported previously. Several critical issues surrounding metallic glass formation and its subsequent micro-structural evolution upon heating are discussed in light of these results.