The Formation of Nanoparticles and Their Competitive Interaction with Twins during Eutectic Si Growth.

In order to investigate the competitive interaction between nanoparticles and twin, the eutectic Si microstructures in Al⁻10Si (wt. %) base alloys with exclusive and combined addition of Sr and Sb are characterized by combined TEM and atom probe tomography (APT). The chemical short range order in Sb⁻Sb and Sb⁻Sr pairs is revealed by ab initio molecular dynamics simulation, which promotes the formation of clusters and nanoparticles. The coexistence of nanoparticles and twins is observed in Sb containing alloys, with a negative correlation in the corresponding number density, owing to the competitive stacking of precursors and individual atoms at the solid⁻liquid interface. Large size particles around 70 nm with a uniform distribution of Sr atoms are formed in Al⁻10Si⁻0.35Sb⁻0.015Sr (wt. %) alloys, due to the precursor aggregation and homogeneous nucleation in the droplets that nucleation are depressed. A model for the formation of nanoparticles and their interaction with twins is proposed.