Phase formation behavior in undercooled quasicrystal-forming AlCuFe alloy melts

Small droplets 10–800 μm in diameter and fine fibers with diameter 10–350 μm and length 2–30 mm and AlCuFe alloy were undercooled and solidified by containerless processing during free fall in a drop tube either in vacuum or at different pressures of purified helium gas. The phases in the samples solidified from the undercooled melt were identified by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A CsCl-type Al(CuFe) cubic phase, Al13Fe4 and AlCuFe icosahedral phase and AlCuFe ternary amorphous phase were found depending on the size and shape of samples. A comprehensive description of phase formation in undercooled AlCuFe melts is developed in terms of nucleation, crystal growth, and transformation kinetics on the basis of classical theories.