X-ray radiography studies of melt convection effects on dendritic evolution in Ga – In alloy


X-ray radiography studies of melt convection effects on dendritic evolution in Ga – In alloy

Shevchenko, N.; Roshchupkina, O.; Eckert, S.

X-ray radiography technique is a powerful tool for investigating solidification processes in metallic alloys. In particular, in-situ X-ray visualization enables a general, intuitive understanding of flow phenomena and dendrite formation in opaque systems. Our work is devoted to the in situ investigation of the dendritic growth during a bottom-up solidification of a Ga-25wt%In alloy under natural and forced convections. Natural convection occurs during the bottom-up solidification because a lighter solute is rejected during crystallization. Forced convection has been produced by a specific electromagnetic pump. The direction of forced melt flow is almost horizontal at the solidification front.
Melt flow induces various effects on the dendrite morphology primarily caused by the convective transport of solute. Our investigations show a facilitation of the growth of primary trunks or lateral branches, suppression of side branching, dendrite remelting, fragmentation or freckle formation. Typical radiographs of stabilized segregation freckles are shown in Fig. 1. We demonstrate that the actual manifestation of all phenomena depends sensitively on the dendrite orientation, the local direction and intensity of the flow. Forced flow eliminates solutal plumes and damps local fluctuations of solute. A preferential growth of the secondary arms occurs at the upstream side of the dendrites, whereas high solute concentration at the downstream side inhibits the formation of secondary branches. Flow patterns and local solute concentration were quantified by image analysis and related to the experimental conditions. These in situ experiments provide benchmark data that can be used to validate simulations of dendritic growth or channel segregations.

Keywords: X-ray radiography; solidification; dendrites; segregation; convection; electromagnetic stirring

  • Invited lecture (Conferences)
    The 4th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR2016), 11.-15.05.2016, Xi’an, China

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Publ.-Id: 24486