Observation of segregation freckle formation under the influence of melt convection


Observation of segregation freckle formation under the influence of melt convection

Shevchenko, N.; Boden, S.; Eckert, S.; Gerbeth, G.

An undesired phenomenon associated with natural convection in the mushy zone is the formation of segregations channels, the so-called chimneys. We investigated the influence of melt flow on the solidification of a Ga-25wt.In alloy, if the buoyancy-driven flow is interfered by a much stronger electromagnetically-driven flow. For visualizing the process we apply the X-ray radiography which enables a general intuitional understanding of the interaction between solidification and melt flow. The main effect of the flow is determined by the flow-induced redistribution of solute concentration. The consequences are a change of the grow direction of the dendrites and the preference of secondary arm branches for and accelerated and decelerated growth, respectively. The present study demonstrates that a dominating electromagnetic stirring may provoke a unidirectional solute transport in the mushy zone which in turn causes the formation of spacious segregation pattern.

Keywords: solidification; melt flow; forced convection; segregation; freckle formation; X-ray radiography

Permalink: https://www.hzdr.de/publications/Publ-15369
Publ.-Id: 15369