Evolution of the microstructure during solidification of immiscible alloys

The modelling of microstructure evolution during solidification of alloys exhibiting a miscibility gap in the liquid state has made considerable progress during the last decade especially due to research under reduced gravity conditions. The paper discusses some recent experimental and theoretical progresses revealing the importance of all pyhsical processes that occur in a region ahead of the solid/liquid interface where the liquid is is thermodynamically in the two phase liquid regime. These processes are nucleation of the minority phase as drops, their diffusional growth, Stokes sedimentation, Marangoni motion and coagulation of drops. Comparison of experimental results under earth und reduced gravity conditions with theoretical models reveal that these processes occuring while passing the miscibility gap seems to be of more importance than the interaction of the second phase drops with the solid/liquid interface. Advantages and limitations of the theoretical modelling based on population dynamcis are discussed. Finally it is outlined that the progresses made in fundamental research fertilized a new industrial technique to produce plain sliding bearings for automotive applications from such alloys.