The Theory of Diffusional Phase Transformations and Microstructure1

As an aid in the understanding of the development of microstructural features, the theories of diffusional phase transformations are reviewed with emphasis on the problems associated with precipitate growth from supersaturated solid solution. This paper is mainly concerned with those basic thermodynamic and kinetic aspects of transforming systems that influence the size and shape of precipitates. Grain boundary precipitation, Widmanstنtten precipitation, and two-phase cooperative growth are considered, and the roles played in each by volume and interface diffusion, and by interface properties, are discussed.