4. Kinetics for homogeneous spherical and stoichiometric precipitates in a dilute system

This section deals with the description of precipitation kinetics in the ideal case where precipitates are spherical, of low volume fraction (dilute system), of well-defined composition (fixed stoichiometry), germinating in a perfect matrix (without structural defects), all during isothermal processing. A further assumption is that the diffusion mechanism consists of isolated solute atom jumps (called monomers). It should be stressed that this ideal situation is never actually encountered in practice. Indeed, in a dilute system, supersaturation is low, which tends to favor heterogeneous rather than homogeneous precipitation.

The different levels of complexity brought about by the successive relaxation of these different approximations are discussed in the following sections.

Here, the mean-field description takes on its full meaning: as...