Segregation of Alkaline Earth Atoms Affects Prenucleation at L-Al/γ-Alumina Interfaces

Abstract

Segregation of foreign atoms on a solid substrate in a liquid metal modifies the geometry and chemistry of the substrate surface and, correspondingly, its potency to nucleate a solid metal. We here investigate the effects of the segregation of alkaline earth (AE) atoms, Mg, Sr, and Ba, at the interfaces between liquid Al and γ-Al2O3{1 1 1} substrates using an ab initio molecular dynamics method. This study reveals the high stability and localized nature of the segregated AE atoms at the oxide substrates. The segregation of the AE atoms induces reconstruction of the metal atoms terminating the oxide substrates, and causes atomic roughness of the substrate surfaces. The content of the induced atomic roughness relates to the ionic size of the AE atoms. Correspondingly, the potency of the oxide substrates is modified. This indicates the possibility of manipulating the substrate potency via segregation of selected impure atoms, which would help to control solidification processes.