Effect of Substrate Chemistry on Prenucleation

Understanding atomic ordering in a metallic liquid adjacent to a solid substrate is of both scientific and technological importance. In this study, we used ab initio molecular dynamics (MD) simulations to investigate systematically the effect of substrate chemistry on atomic ordering in the liquid adjacent to artificially created substrates that have the same crystal structure as the solid phase upon solidification but different chemical characteristics. We found that for a given liquid, an attractive chemical interaction (negative heat of mixing) between the liquid and the substrate strengthens atomic ordering in the liquid at the interface, while a repulsive interaction (positive heat of mixing) weakens atomic ordering. It is realized that although both structure and chemistry of the substrate affect atomic ordering in the liquid adjacent to the liquid/substrate interface, the structural effect dominates the atomic ordering process, while the chemical effect is but a secondary factor and affects atomic ordering through either strengthening or weakening the structural templating. Such knowledge of atomic ordering may help us to understand both prenucleation and heterogeneous nucleation, and to develop more effective approaches to grain refinement during solidification through effective manipulation of the interplay between structural and chemical effects of the substrate on atomic ordering in the liquid adjacent to the interface.