The processing path of a structural material controls the development of its microstructure, and the formation of defects that ultimately dictate its properties and performance. From a fundamental standpoint, complex solidification microstructures, such as dendrites, arise from a subtle interplay between phenomena occurring at much different scales: from atom attachment kinetics, to microscopic interfacial phenomena, to macroscopic transport of heat and species in the different phases. Hence, solidification modeling represents a challenge to bridge length and time scales, and the fundamental understanding of solidification still holds long-standing unknowns, such as the mechanisms of intra- and inter-grain dendritic microstructure selection, or the origin of morphological transitions in casting.

This talk will highlight three approaches for simulating solidification at different scales, from a single dendrite (~ μm) to a grain structure (~ cm), namely: phase-field modeling, a new multiscale “dendritic needle network” model, and classical volume-averaging methods. At each scale, simulations are used to reveal salient mechanisms of microstructure development in alloys, specifically pertaining to the selection of dendritic spacings, grain boundaries, and phases. Studies are motivated and illustrated by joint experimental measurements, for instance in situ observation of directional solidification, containerless processing of electromagnetically levitated metal droplets, and powder atomization for catalysts production. Some remaining outstanding challenges and missing links will be highlighted, as well as potential strategies to address them and ongoing efforts in linking predicted microstructures to mechanical properties.