Cluster dynamics modeling of precipitation kinetics:: Recent developments

Cluster dynamics (CD) is used to model at the atomic to mesoscopic scale the kinetics of first order diffusional phase transformations like solid solution unmixing or ordering. Clusters are embryos of the growing phase. The kinetics of the transformation is modelled through the numerical solving of a set of master differential equations. describing in cluster space the intercluster matter exchanges. These exchanges. absorption and emission of solute atoms. are controled by the solute diffusivities and the cluster intrinsic free energies. The application of CD to multicomponent systems is given here for the first time in a ternary alloy for the precipitation of a Ll(2)Al(3)(Zr,Sc) phase in an AlZrSc solid solution. Results are discussed in relation to classical approaches. The CD indirect coupling of cluster growth and shrinkage, enlights features which are at variance with the classical nucleation theory.