5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

Prenucleation refers to the phenomenon of atomic ordering in the liquid adjacent to the liquid/substrate interface at temperatures above the nucleation temperature, which becomes the precursor for the subsequent heterogeneous nucleation process through structural templating. Understanding of prenucleation is therefore of both scientific and technological importance. Based on recent investigations of the effects of lattice misfit and chemical interactions on prenucleation, in this work we study atomic ordering adjacent to the surfaces of native oxides (alumina, magnesia) in Al and Mg melts, using a parameter-free ab initio molecular dynamics simulation (MD) technique based on the density-functional theory (DFT). Our modelling reveals that in liquid, the oxide surfaces exhibit a rich variety of 2D ordered structures containing various structural defects, depending on the structural nature of the substrate and chemical interactions between the substrate and the liquid metal. Formation of atomically rough substrate surfaces was observed on the oxide particles in both Mg and Al melts during the ab initio MD simulations. This atomic roughness of the substrate surface weakens prenucleation and reduces significantly the potency of oxide particles as substrates for heterogeneous nucleation.