Abstract

Co-author: Stephen Davis (Northwestern University)

High-porosity metallic solids are useful as lightweight materials in many engineering disciplines. However, batch processing techniques for producing such materials by solidification of a molten metallic foam are problematic, and it is not currently possible to control the porosity distribution of the final product {it a priori}. The molten metallic foam is inherently unstable; the thin liquid bridges between bubbles drain rapidly and rupture due to intermolecular forces, leading to bubble coalescence and large-scale topological rearrangement. In this talk we will consider the competition between coalesecence and freezing in these dynamically evolving foams, examining in particular the coupling between the microscale hydrodynamics in the molten liquid films and the progression of a solidification front. The foam is modelled as a coupled system of free boundary problems involving both liquid/gas and liquid/solid interfaces, which we solve using a combination of asymptotic and numerical techniques. An understanding of these microscale processes motivates other protocols for solid foam production where the porosity distribution of the final product can be more effectively controlled.