Dendrite growth under a forced convective flow: A review

As one of the representative patterns in nature and laboratory experiments, dendritic structures control the properties of a broad range of advanced materials. Dendrites arise during different phase and structural transformation processes. Generally, the formation of dendritic structures are stipulated by transport processes in bulk phases, together with thermodynamic properties and kinetic phenomena at the phase interfaces. The formation of a dendritic microstructure under the influence of external fields (electromagnetic and gravitational) is considered in this review. These fields involve the liquid and gaseous phases in a forced convective flow, causing the transfer of energy and matter in addition to the usual conductive (diffusion) transport. The formulated model takes into account rapid solidification from an undercooled liquid phase as well as intermediate and low growth velocities of dendritic crystals in pure one-component systems extended to binary mixtures and alloys. The areas of undercooling are identified, in which the influence of convection caused by the electromagnetic and/or gravitational field is most noticeable. The solidification regimes (from the diffusion-limited mode to the thermally and kinetically controlled mode) are reviewed in connection with the different liquid flow velocities that dictate various boundary conditions (conductive and convective) on the surface of growing crystals. A comparison of model predictions with experimental data and computational results provides the grounds for a discussion about the applicability of the formulated model to interpreting known and unexpected phenomena in the formation of a crystalline structure. By changing the power of the considered fields or reducing them almost to zero (for instance, in microgravity), it is possible to control the dispersion of a dendritic microstructure, as well as separate accompanying phases (eutectic, peritectic, monotectic, intermetallic phases, etc.) during the solidification of materials and, in the general case, during phase transformations.