Solidification and Crystal Growth Dynamics in Eutectic Systems
The cooperative or diffusively coupled growth of multiple phases during solidification is one of the most widely observed and generally important classes of phase transformations in materials. Technologically, due to having lower melting points compared with their pure components, and small freezing ranges, these alloys have excellent fluidity exhibited during casting and favorable properties offered by the fine composite structures both of which contribute to the wide application of eutectic alloys in the casting, welding, and soldering of engineered components. Academically, the topic of eutectic solidification offers a wealth of rich problems involving multicomponent thermodynamics, solid-liquid and solid-solid interfacial phenomena, morphological stability, chemical and thermal diffusion, and nucleation phenomena. Surprisingly, despite the broad-based technological and academic importance, many fundamental questions regarding eutectic solidification remain unanswered. This lack of understanding severely limits our ability to employ computational methods in the prediction of microstructure for the effective design of new materials and processing techniques through simulation.
In this study, solidification and crystal growth dynamics in rod eutectics are investigated by performing systematic directional solidification experiments with various eutectic systems and phase field simulations. Significant influence of the slide geometry on the rod morphology, even for specimen thicknesses, which are many times greater than the characteristic eutectic spacing, has been observed experimentally and confirmed by the numerical simulations. Additionally, effects of anisotropy on eutectic grain have been investigated using a new technique called rotating directional solidification. This setup permits us to change the in-plane orientation of the crystals with respect to the thermal gradient continuously, while keeping their relative orientation constant, and to observe the solidification front in real time by videomicroscopy. Respectfully, eutectic grains have been classified into three main groups regarding their gamma-plot of the interphase boundaries (Wulff plot). These results are significant not only for the materials science community but also for the out of equilibrium pattern formation dynamics branch of nonlinear physics.