TY - CONF

T1 - Investigation on the Liquid Flow ahead of the Solidification Front During the Formation of Peritectic Layered Solidification Structure

AU - Mogeritsch, Johann

AU - Pfeifer, Tanja

AU - Stefan-Kharicha, Mihaela

AU - Ludwig, Andreas

PY - 2018/9/2

Y1 - 2018/9/2

N2 - Several studies have been carried out over the last decades to deepen our understanding of peritectic microstructure formation by using the Bridgman technique. In metals, the formation of layered structures, including bands, island-bands or peritectic coupled growth have been observed post-mortem by analyzing quenched samples. To explain these structures, different theoretical models have been published. Instead of taking metals, organic transparent compounds that show a peritectic region are currently used in this study. This technique pro-vides the advantage of observing in-situ the formation of peritectic morphologies and the dy-namics of the solid/liquid interface. Visualizing the flow pattern that occurs during the evolu-tion of the peritectic microstructures represents major progress in this discipline. In order to do so, the organic binary system TRIS-NPG was used as model substance and seeding particles as tracers. It was possible to observe (i) the effect of the mushy zone and its influence on the liquid flow ahead of the solid/liquid interface, for a resting sample, and (ii) the flow pattern during solidification of peritectic layered structures. We found that during the evolution within the mushy zone, an upward movement of liquid through temporarily existing liquid channels into the melt, ahead of the solid/liquid interface takes place. Thus, during solidifica-tion, the solutal-buoyancy-driven flow pattern that forms in front of the solid/liquid interface is occasionally interrupted by fine upward flows, called micro-plumes. On the one hand, the formation of banded structures is favorable, since the peritectic phase grows via the existing liquid channels within the initial primary phase. Whereby, the formation of the peritectic lay-ered structures seems to be not influenced by the micro-plumes. On the other hand, the spreading of the primary phase in a lateral direction along the solid/liquid interface of the just-formed peritectic phase is probably hindered by micro-plumes.

AB - Several studies have been carried out over the last decades to deepen our understanding of peritectic microstructure formation by using the Bridgman technique. In metals, the formation of layered structures, including bands, island-bands or peritectic coupled growth have been observed post-mortem by analyzing quenched samples. To explain these structures, different theoretical models have been published. Instead of taking metals, organic transparent compounds that show a peritectic region are currently used in this study. This technique pro-vides the advantage of observing in-situ the formation of peritectic morphologies and the dy-namics of the solid/liquid interface. Visualizing the flow pattern that occurs during the evolu-tion of the peritectic microstructures represents major progress in this discipline. In order to do so, the organic binary system TRIS-NPG was used as model substance and seeding particles as tracers. It was possible to observe (i) the effect of the mushy zone and its influence on the liquid flow ahead of the solid/liquid interface, for a resting sample, and (ii) the flow pattern during solidification of peritectic layered structures. We found that during the evolution within the mushy zone, an upward movement of liquid through temporarily existing liquid channels into the melt, ahead of the solid/liquid interface takes place. Thus, during solidifica-tion, the solutal-buoyancy-driven flow pattern that forms in front of the solid/liquid interface is occasionally interrupted by fine upward flows, called micro-plumes. On the one hand, the formation of banded structures is favorable, since the peritectic phase grows via the existing liquid channels within the initial primary phase. Whereby, the formation of the peritectic lay-ered structures seems to be not influenced by the micro-plumes. On the other hand, the spreading of the primary phase in a lateral direction along the solid/liquid interface of the just-formed peritectic phase is probably hindered by micro-plumes.

KW - organic model system

KW - peritectic layered structures

KW - Bridgman-furnace

KW - plumes

KW - thermos-solutal convection

M3 - Paper

SP - 319

EP - 324

ER -