Cellular solidification microstructures

Connection between Transport Processes and Solid Microstructure. The formation of cellular and dendritic patterns in the microstructure of binary crystals grown by directional solidification results from interactions of the temperature and concentration fields with the shape of the melt-crystal interface. Tiller et al. (21) first described the mechanism for constitutional supercooling or the microscale instability of a planar melt-crystal interface toward the formation of cells and dendrites. They described a simple system with a constant-temperature gradient G (in Kelvins per centimeter) and a melt that moves only to account for the solidification rate Vg. If the bulk composition of solute is c0 and the solidification is at steady state, then the exponential diffusion layer forms in front of the interface. The elevated concentration (assuming k < 1) in this layer corresponds to the melt that solidifies at a lower temperature, which is given by the phase diagram (Figure 5) as... 

The current part of the present chapter has had as its aim the use of the study of microstructural evolution as a case study in the techniques for bridging scales described earlier in the chapter. The examples that were recounted in our discussion of microstructure and its evolution drew from a variety of the resources discussed earlier in the chapter in the context of bridging scales . In particular, we have seen how kinetic Monte Carlo models adopt an information passage philosophy in which calculations of one type are used to inform those of another. Similarly, the description of solidification, including information on the local crystal orientations, using a linkage of cellular automata with continuum descriptions of heat flow illustrates how more than one computational scheme may be brought under the... 

---