Objects interacting with solidification fronts: Thermal and solute effects

Objects, such as droplets, bubbles, or particles, interact with a moving solidification front in several material processing routes. The consequences of this confrontation, varying from instantaneous engulfment to complete rejection of suspended objects, regulates the solidified microstructure and thus, the functional properties of the material. In this study, we utilize in situ cryo-confocal microscopy to investigate the interplay between thermal conductivity mismatch (of the object and the melt) and the role of solute, which both impact the geometry of the ice-water solidification front in different manners. First, we experimentally validate the theoretical predictions of physical models on the distortion of thermal fields in the presence of foreign objects. Subsequently, we report on the dominating effect of solute on the front curvature with the dynamic evolution of premelted films. In the case of cellular front morphology, we depict that particles with a lower thermal conductivity than water induce a distortion of the encircling ice crystals, thereby modifying the final microstructure of the solid. Finally, our results demonstrate that to successfully predict and control the solidification microstructure, in the presence of objects, physical models incorporating both thermal and long-range solute effects are required.