Papers by Author: A. Weiß

Abstract: The movement and morphological change of a solid-liquid interface in directional solidification was investigated during two sounding rocket flights. By using the transparent binary alloy Succinonitrile-Acetone the dynamic processes at the solidification front could be observed directly. Both the planar interface growth, the onset of instability and the characteristic features of the interface morphology, i.e. the evolution of the primary spacing and amplitudes of the cells and dendrites were evaluated. The comparison with a calculation of the morphological instability based on the theoretical model of Warren and Langer showed a good agreement concerning the critical time and velocity of the solidification front.

Abstract: A global numerical model of a Bridgman furnace is developed and validated. The model includes heat transfer due to radiation and conduction in a stationary setup. The rotating magnetic field (RMF) device mounted on the facility is implemented into the model also. A numerical study on the flow field caused by the axial non-uniform RMF and natural convection is performed, helping to get a better understanding of the convective conditions during the directional solidification experiments.

Abstract: AlSi7Mg0.6 alloys are directionally solidified with forced melt flow induced by a rotating magnet ring. By increasing the rotational frequency of the permanent magnet the columnar dendritic microstructure in the centre part of the samples changes completely towards a structure of small equiaxed grains with different crystallographic orientations, accompanied by an increased amount of eutectic and Mg2Si phases.

Abstract: The MICAST research program focuses on a systematic analysis of the effect of convection on the microstructure evolution in cast Al-alloys. The experiments of the MICAST team are carried out under well defined thermally and magnetically controlled, convective boundary conditions and analyzed using advanced diagnostics and theoretical modeling, involving phase field simulation, micro-modeling and global simulation of heat and mass transport. The MICAST team uses binary, ternary and technical alloys of the Al-Si family. This paper gives an overview on recent experimental results and theoretical modelling of the MICAST team.