Diffusional phase transformations on the atomic scale: Experiment and modeling

In the early stages of phase transformations, microstructures are generated with the dimensions of only a few atomic spacings. Investigation of structures on such a fine scale poses severe difficulties, not only for experimental studies, but also for conventional theories based on continuum models. In this paper the authors report on a combination of atomic-scale microanalysis using the position-sensitive atom probe and atomistic simulations using the dynamic Ising model. Three phase transformations have been studied: spinodal decomposition in Fe-Cr alloys, nucleation and growth in dilute Cu-Co alloys and finally a conditional spinodal reaction in Ti-Al. The model provided a good quantitative match to the kinetics of spinodal decomposition observed in Fe-45%Cr, and nucleation and growth in Cu-1%Co. It also predicts the development of coupled ordering and phase separation in Ti-15%Al.