Presentation Dr. Mathiesen


Ragnvald H. Mathiesen
SINTEF Materials and Chemistry, Trondheim, Norway,

Solidification processes evolve as complex self-assembly structures influenced by several interacting mechanisms such as thermal and chemical diffusion, melt convection, solid flow, melt segregation at various length scales, formation of defects such as micro pores, or cracks (hot-tears) induced from a combination of thermal strains and inappropriate melt feeding, etc. Also, solidification of a binary or multi component alloy generally involves simultaneous growth of more than one phase, often with different growth modes realized for the different segregates. The physics describing a full scale casting must account for phenomena occurring over length scales from the atomic (interface attachment kinetics, nucleation) to the macroscopic (macro segregation, freckles), over a typical time-scale from μs (thermal diffusion controlled growth) to minutes (coarsening). The morphology and propagation of solid-liquid interface is bound by limits set by diffusion/convection, typically with characteristic lengths in the μm-regime.
While numerical computer modelling for simulations covering the range from solidification fundamentals to full scale castings has advanced considerably over the last couple of decades, provision of new experimental data to guide theory and modelling and assist in their refinement has fallen behind. In the past in-situ studies of solidification has been limited to video microscopic investigations on a few suitable optically transparent organic model systems. However, these systems are severely limited as analogues to real alloys, and can only be used to realize a limited number of growth modes and phenomena. Recent improvements in X-ray detectors combined with the eminent brightness and collimation offered at 3rd generation synchrotron sources has opened for X-ray radiography investigations at spatiotemporal resolutions approaching that of video microscopy. Here, in-situ X-ray imaging observations from studies of solidification fundamentals in Al-Cu eutectics and Al-Bi(Zn) monotectics will be presented, and quantitative results extracted from the experimental data will be compared with results from theory and modelling. The X-ray imaging experiments has been carried out at the ID22 microfocus/imaging beamline at the ESRF.

Zeit: 30.11.05, 10.00 Uhr
Ort: Kleiner Hoersaal, Geb. 120 (FZR-Campus)