Modelling of microstructure evolution in peritectic systems

Theoretical models for directional solidification microstructures are largely developed for steady-state growth conditions. In the two-phase region of peritectic system, a rich variety of two-phase microstructures form in which the two phases often form under non-steady-state conditions and the microstructure evolution depends on the nucleation characteristics of the two phases as well as on the competitive growth of the two phases under dynamical growth conditions. Theoretical models, based on nucleation and diffusive growth, are presented to establish the mechanisms that lead to different microstructure formation in peritectic systems. The critical role played by nucleation in the selection of oscillatory microstructures is discussed, and experimental studies to select different nucleation sites are described. Experimental studies in the Sn-Cd system are carried out in thin capillary samples to minimize fluid flow effects that are dominant in most experiments. Critical conditions for the observation of composite microstructures are evaluated. These results will be presented to support the predictions of the models.