Modelling and simulation of the freeze casting process with the phase-field method

The freeze casting process is a novel manufacturing method for both near net-shape parts as well as directed porous structures as employed by filters and implants. Depending on the choice of liquid and processing conditions a very wide range of pore shapes and sizes can be achieved. In order to predict the resulting microstructure, a phase-field model is developed on the basis of the grand potential formalism. The model and its parametrization approximate the freeze-casting process of water by linking its thermodynamics with established theory. Directional solidification simulations with varying suspension concentrations, velocities and temperature gradients are carried out. From these, microstructural lengths are determined and linked with the processing parameters, so as to derive linkages between the microstructure and the processing conditions

Scale-bridging phase-field simulations of microstructure responses on nucleation in metals and colloids

In the present studies we investigate the connection between atomistic simulation methods, i.e. molecular dynamics (MD) and phase-field crystal (PFC), to the mesoscopic phase-field methods (PFM). While the first describes the evolution of a system on the basis of motion equations of particles the second uses a Cahn–Hilliard type equation to described an atomic density field and the third grounds on the evolution of continuous local order parameter field. The first aim is to point out the ability of the mesoscopic phase-field method to make predictions of growth velocity at the nanoscopic length scale. Therefore the isothermal growth of a spherical crystalline cluster embedded in a melt is considered. We also show simulation techniques that enable to computationally bridge from the atomistic up to the mesoscopic scale. We use a PFM to simulate symmetric thermal dendrites started at an early stage of solidification related to nucleation. These techniques allow to simulate three dimensional dendrites from the state of nuclei (≈50 Å) converted from MD up to a size of some μm where ternary side-arms start to grow

On counting cells in open pore foams

The number of cells in a sample of an open pore foam is usually expressed as ppi (pores per inch), but it is not easy to deduce the total number of cells in a sample from this information. In this paper we derive a linkage between the cell number of a foam sample, the volume fraction of the solid and the mean thickness of its ligaments by means of computer simulations