Solidification microstructures: A conceptual approach

Detailed theoretical models have been developed in the literature to correlate microstructural characteristics as a function of processing parameters. 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 lengths of the important physical processes. Initially, the important physical processes of solute and thermal transport and capillarity effect are considered, and they are related to the microstructural lengths such as dendrite tip radius, primary and secondary spacing, and eutectic 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 lengths that become important under rapid solidification are then developed, and how these characteristic lengths influence microstructural transition and microstructural scales is also discussed.