Chemical, structural and electronic characterization of solid-liquid aluminum-silicon alloys using in-situ TEM

Studying solid-liquid interfaces in multi-component alloys is important for understanding the thermodynamic and kinetic behaviors of phases during solidification and melting. Previous investigations pertaining to characterization of solid-liquid interfaces have been limited due to restricted experimental accessibility. In this study, solid-liquid interfaces in atomized powders of hypereutectic Al-Si based alloy were investigated using in-situ transmission electron microscopy (TEM). A thermal shield developed during 'the study allowed chemical characterization of solid-liquid interfaces and phases to be performed as a function of temperature, thereby directly determining solute partitioning and the metastable phase boundary of the undercooled liquid. In addition, kinetic analyses involving the nucleation, growth and dissolution behaviors of primary Si and the Al solid-solution were also performed. The morphological evolutionary paths of primary Si and the Al solid-solution were found to be fundamentally different due to the underlying interfacial energetics. Moreover, electron energy-loss spectroscopy (EELS) was used to study the variation in plasmon energy as a function of temperature in liquid and solid phases and across the solid-liquid interface. The plasmon energy-temperature trend in the liquid alloy was found to be markedly different from the case of pure liquid Al, revealing the electronic effects of alloying additions to the liquid phase. The energy-loss near edge structures (ELNES) of the liquid alloy also showed remarkably different electronic structure of the unoccupied density of states (DOS) in comparison to pure liquid Al, indicating a fundamental electronic structure variation in the liquid due to solute additions.