SOLIDIFICATION MICROSTRUCTURES - A CONCEPTUAL-APPROACH

Detailed theoretical models have been developed in the literature to c orrelate microstructural characteristics as a function of processing p arameters. These results are examined with a broad perspective to show that various laws for microstructural transitions and microstructural spacings can be represented in terms of three simple characteristic l engths of the important physical processes. Initially, the important p hysical processes of solute and thermal transport and capillarity effe ct are considered, and they are related to the microstructural lengths such as dendrite tip radius, primary and secondary spacing, and eutec tic spacing. It is shown that these microstructural lengths are simply given by the geometric mean of the characteristic lengths of physical processes that are important in a given problem. New characteristic l engths that become important under rapid solidification are then devel oped, and how these characteristic lengths influence microstructural t ransition and microstructural scales is also discussed.