Micro-macroscopic modelling of binary alloy solidification

Aim of project
The project concerns computer simulation of multi-scale transport phenomena accompanying binary alloy solidification and the validation of the proposed models through comparisons of their predictions with experimental findings from the laboratory arrangements designed for this purpose. Theoretical part of the research involves the development of macroscopic computer simulation models based on the volume and/or ensemble averaging of microscopic equations of mass, momentum, species and energy transfer, and on the original front tracking technique on a fixed control-volume grid. The latter method, basing on the predicted dendrite tip kinetics, enables the separation of the columnar dendrite zone from the under-cooled liquid/ equi-axed grain region within the two-phase (mushy) zone. Thus, it provides the potential for the use of different, and so more precise, modelling of these two varied crystal structures. Using the developed computational models, further research focuses on the analysis of the influence of thermo-solutal natural convection on kinetics of dendrite growth, individual grain shapes, the potential for equi-axed structure development, and compositional heterogeneity growing on the whole system scale. Effective coupling between micro- and macroscopic transfer processes in the simulation model is also widely addressed in the project, where the combination of ensemble averaging approach and the Green function theorem is used to provide means for the realization of mutual dependencies between micro-fields and macro-fields of velocity, temperature and species concentration. The main objective of the experiments, conducted with transparent metal alloy analogues, is to provide images of: the growth of an individual crystal, developing dendritic structures, their dynamics and shapes of the mushy zone, and to visualize detailed velocity and temperature fi elds. These experimental data are used to validate both new models of dendrite growth and the calculated macroscopic fields of velocity and temperature.

Expected results
New models of dendrite tip kinetics and further development of the front tracking method for multi-dimensional binary alloy solidification driven by thermo-solutal convection. New approach to the mutual coupling between micro- and macro- scales phenomena in effective macroscopic modeling of binary alloy solidification.