Interactive Dynamics of Fluid Flow and Interface Microstructure in Directional Solidification of Alloys

摘要

In directional solidification of bulk alloys, fluid flow induces specific patterns at the solid-liquid interface, and vice versa. In particular, morphological instability of the smooth interface and micro-structure selection take place according to the solute macrosegregation induced by convection. In transparent succinonitrile-acetone samples grown upwards, birth of morphological instability and cell formation are first observed along the walls of the convective cells where solute is accumulated, in agreement with recent predictions of Chen and Davis. Ultimately, an asymptotic state is reached in which cells are not uniform, and may coexist with dendrites. In Al-1.5 wt% Ni alloys, fluid flow induces dendrite clustering due to Ni enrichment of the melt on the periphery of the sample, where eutectic growth is observed. When faceted cells form, microconvection on the cell scale driven by solute and/or thermal gradients may effect the solid-liquid interface morphology, as discussed for directional solidification of Bi-1wt% Sb, a semiconductor system with intermediate kinetics.