Microstructural Evolution in Undercooled Al–8wt%Fe Melts

Abstract

Containerless rapid solidification of hypereutectic Al–8wt%Fe is investigated experimentally using the Impulse Atomization technique (IA), as well as ElectroMagnetic Levitation (EML) under terrestrial and reduced gravity conditions. The samples were analyzed using scanning and transmission electron microscopy, X-ray and neutron diffraction, as well as electron backscattered diffraction. In both EML and IA, the samples experience some undercooling for the solidification of the primary intermetallic phase, which is likely metastable Al_mFe (m = 4.0–4.4). After recalescence, the solidification path then continues with the nucleation and growth of stable Al₁₃Fe₄. While Al₁₃Fe₄ dominates in EML samples, it becomes minor in favor of Al_mFe in IA droplets. The morphology differences of the primary intermetallics growing under terrestrial and microgravity conditions in EML are clear with acicular morphology for the former and a star-like morphology for the latter. The α–Al has a strong texture in microgravity EML and in IA samples while a weak one is observed on terrestrial EML. This difference is attributed to the weaker fluid flow occurring under reduced gravity conditions and in IA droplets.