Complex interface geometries in phase transformations

In phase transformations complex geometries can form along the phase boundaries. In some cases the development of the morphology of interfaces can be understood qualitatively as well as described quantitatively. Examples of this are the interpenetrating structures of tungsten carbide and cobalt in hard metals, the dendritic structures in Al-Cu, microstructural inhomogeneities formed by recrystallisation, "fractal" microstructures in the martensitic transformation and the microstructures of sintered materials. In other cases however effects are observed which still require a clear explanation. Examples of these are the cellular structures and canals which are observed after solidification in systems with decreasing solubility and after peritectic transformation. In this article the work carried out to gain a better understanding of these little known phenomena and the complex microstructural geometries of their formation mechanisms are discussed.