In-situ observation of transient columnar dendrite growth in the presence of thermo-solutal convection

Abstract

The time evolution of tip radii and velocities of growing columnar dendrites have been extracted from an image sequence measured in situ by synchrotron X-ray video microscopy during directional solidification of Al-15%Cu-9%wtSi alloy. At the scale of the primary dendrites, a highly transient growth was observed in conjunction with liquid flow caused by modest thermo-soutal convection. The nominal spatial and temporal resolutions employed in the experiment were 1.4 μm at approximately 100ms frame rate, respectively. A very prominent mutual inter-relation between the solute field and flow velocity field and the dendrite growth rate and morphology is evident in these observations. Image processing allowed extraction of the corresponding projection averaged solute field in each frame, and an estimate of the solute boundary velocity field by frame-to-frame tracking of its motion. These measurements may eventually support development of statistical dendrite kinetics models for transient states in alloy solidification processes that could be applied in microscopic scale solidification models such as phase field. © Published under licence by IOP Publishing Ltd.