Ab Initio Molecular Dynamics Investigation of Prenucleation at Liquid–Metal/Oxide Interfaces: An Overview

Abstract

Prenucleation refers to the phenomenon of atomic ordering in the liquid adjacent to a liquid/solid interface at temperatures above its nucleation temperature. It produces a precursor for heterogeneous nucleation in the liquid and thus has a strong influence on the nucleation process. Oxide particles, including magnesia, spinel, and alumina, are inevitably formed in the liquid during liquid–metal handling and casting. They may act as nucleation sites for potential grain refinement. Knowledge about prenucleation at liquid–metal/oxide (M(l)/oxide) interfaces is important for an understanding of heterogeneous nucleation during casting. Here, we present an overview of the recent studies on the prenucleation at the M(l)/oxide interfaces using ab initio molecular dynamics simulation techniques. We observed a wide variety of interfacial chemistry and identified the formation of an ordered metal layer terminating the oxide substrates, such as MgO{1 1 1} (denoting MgO with {1 1 1} surface termination), α-Al2O3{0 0 0 1}, MgAl2O4{1 1 1} and γ-Al2O3{1 1 1} in liquid light metals. The terminating metal atoms are positively charged and form topologically rough layers, which strongly impact the prenucleation at the interfaces. We suggest modification of nucleation potency of the substrate surfaces via elemental segregation to manipulate the solidification processes. This is demonstrated by the segregation of La atoms at the Al(l)/γ-Al2O3 interfaces.