Manipulating Nucleation Potency of Substrates by Interfacial Segregation: An Overview

Abstract

During solidification of metallic materials, heterogeneous nucleation occurs on substrates, either endogenous or exogenous. The potency of the substrates for nucleation is mainly dependent upon the atomic arrangements on the substrate surface, which are affected by the lattice misfit between the substrate and the nucleated solid, the surface roughness at atomic scale, and the chemical interaction between the substrates and the melt. Extensive examinations on metal/substrate (M/S) interfaces at atomic scale by the state-of-the-art aberration (Cs) corrected STEM and associated EDS and EELS have shown that alloying elements in liquid melts tend to segregate at the interfaces, leading to the formation of various 2-dimensional compounds (2DCs) or 2-dimensional solutions (2DSs), depending upon segregation behavior of the elements. For instance, Al3Ti 2DC and Ti2Zr 2DC at the Al/TiB2 interface, Y2O3 2DC at the Mg/MgO interface, and a Si-rich 2DS layer at Al-Si/TiB2 interface have been identified. Such interfacial segregations significantly affect nucleation potency of the substrates, resulting in either promoting or impeding the heterogeneous nucleation process during solidification. In this paper, we present an overview of the current studies of interfacial segregation behavior, the structure and chemistry of interfaces, and their impacts on the subsequent heterogeneous nucleation and grain initiation processes. Our focus is on the advances made in the understanding of the mechanisms for nucleation and grain refinement. It is demonstrated that it is feasible to manipulate heterogeneous nucleation by modifying nucleation potency of a substrate through deliberate interfacial segregation of desirable elements, achieving effective control of the grain structure of cast metallic materials.

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

“…Ma, et al observed Cu segregation at the Al/α-Al 2 O 3 interfaces [25]. Recently, segregation of the nd 1 elements, La or Y, at the Al/γ-Al 2 O 3 {1 1 1} interfaces has been realized experimentally and observed by TEM techniques [26]. Meanwhile, theoretical approaches, especially parameter-free AIMD methods, have been employed to investigate the atomic ordering at interfaces between liquid metal and oxide substrates [16,[27][28][29].…”

Nucleation Work on Curved Substrates

“…Using ab initio molecular dynamics simulations, Wang et al [24] showed that heterogeneous nucleation plays an important role in the atomic arrangement of the substrate surface, which is influenced by the lattice misfit between the melt and solid, surface roughness, and the chemical interaction at the phase interface.…”