Dendritic crystal growth in pure materials

Dendritic growth is a fundamental crystal growth phenomenon accompanying most casting and solidification processes, and, occasionally, occurring during the growth of single crystals, where it is detrimental to crystalline quality. Dendrites are the ubiquitous crystal form in freezing alloys and supercooled melts, because their shapes are most suited for efficient heat and mass transfer at small scales. Dendritic scales are typically the smallest length scales of interest in ingots and castings, typically associated with: (1) chemical processes, such as microsegregation, (2) thermal processes, for example, latent heat release, and (3) mechanical processes, for instance, the volume change during phase transformation. All of these processes operate at the dendritic solid-melt interface. Understanding dendritic growth is therefore considered essential for controlling basic solidification and crystal growth processes. A brief history of dendrites will be sketched, showing how the subject of dendritic solidification evolved to its present status as a modern sub-field of general crystal growth. The comprehensive understanding of dendrites and developing a predictive capability of practical utility to the crystal grower, however, remain as works in progress. The subject of dendritic growth will be presented on the basis of heat and mass transfer, capillarity effects at the solid melt interface, and interfacial dynamics, including morphological stability, and side-branching dynamics. Experimental verification of dendritic scaling laws using microgravity experimentation is included as a brief attempt to encapsulate this important subject within crystal growth science. (C) 2003 Published by Elsevier B.V.