IMPROVED ANALYSIS OF TIP UNDERCOOLING IN CELLULAR SOLIDIFICATION OF A BINARY ALLOY

Classical expressions for the undercooling, DELTAT, at the tip of a cell during arrayed-directional solidification of a binary alloy, are compared with the experimental data on succinonitrile-acetone alloys. The range of validity of existing cellular models on cell tip undercooling is then determined. It is shown that cellular growth is an intricate situation in which the cell shape and the solute partitioning coefficient need to be properly included in the analysis. An improved analysis of cellular tip undercooling is developed, and the results presented in terms of an intrinsic solutal undercooling, DELTAT(s), and a part, DELTAT(SMI), that is associated with the simultaneous existence of a shape (S) and some morphological instability (MI).