Nucleation and Growth

Abstract

A vast majority of metallurgical transformations take place by nucleation of stable nuclei of product phase, followed by their and growth. Roasting of sulphides, decomposition of carbonates, etc., all produce new phases. Decarburization of iron carbon melts proceeds by nucleation and growth of CO bubbles. Condensations of vapours, freezing of liquids, melting of solids, precipitation processes are all examples of nucleation and growth processes. The phase transformations that may take place when a single phase alloy α is cooled from a temperature at which it is stable to a temperature at which it becomes unstable are of considerable technological interest. Solidification and allotropic transformation are examples of polymorphous phase transformation, which involves only change of structure. In the other type of phase transformation, the compositions of parent and product phases differ. In most instances, this is associated with changes in structure as well. Only in a minority of reactions like precipitation of Guinier–Preston zones (G. P. zones), e.g. in Al–Cu alloys, the two phases have identical crystal structures and orientations.