TY - THES

T1 - Estimation of convection ahead of a solid/liquid interface during solidification of layered peritectic solidification morphologies

AU - Pfeifer, Tanja

N1 - no embargo

PY - 2018

Y1 - 2018

N2 - The present study will emphasize on the investigations of the effect of convection on the formation of peritectic layered structures near the constitutional undercooling by using the binary organic peritectic model system TRIS–NPG. Under conditions where both phases solidify in a planar manner it is possible that for peritectic concentrations the metastable phase nucleates before the initial phase reaches steady state. This enables a competitive growth between the primary and the peritectic phase which leads to peritectic layered structures. Investigation on metal alloys exhibited various layered microstructures in form of bands, island bands, and peritectic coupled growth similar to eutectic structures. Since such structures are highly influenced by convection in-situ investigations were done to make visible the flow pattern and to observe the corresponding dynamic of the solid/liquid interface. The experimental procedure was carried out by directional solidification in a Bridgman-furnace and the material was enriched with tracers to visualize the convection. The investigations on the organic model system TRIS–NPG indicated different forms of flow pattern. The fact that the particles show that convection influence the formation of layered structures was a major finding in this project. Another important observation was the influence of liquid channels and micro-plumes within the mushy zone on the evolution of bands in lateral direction.

AB - The present study will emphasize on the investigations of the effect of convection on the formation of peritectic layered structures near the constitutional undercooling by using the binary organic peritectic model system TRIS–NPG. Under conditions where both phases solidify in a planar manner it is possible that for peritectic concentrations the metastable phase nucleates before the initial phase reaches steady state. This enables a competitive growth between the primary and the peritectic phase which leads to peritectic layered structures. Investigation on metal alloys exhibited various layered microstructures in form of bands, island bands, and peritectic coupled growth similar to eutectic structures. Since such structures are highly influenced by convection in-situ investigations were done to make visible the flow pattern and to observe the corresponding dynamic of the solid/liquid interface. The experimental procedure was carried out by directional solidification in a Bridgman-furnace and the material was enriched with tracers to visualize the convection. The investigations on the organic model system TRIS–NPG indicated different forms of flow pattern. The fact that the particles show that convection influence the formation of layered structures was a major finding in this project. Another important observation was the influence of liquid channels and micro-plumes within the mushy zone on the evolution of bands in lateral direction.

KW - Peritektic Erstarrung

KW - Transparente organische Systeme

KW - Bridgman-Ofen

KW - Phasendiagramm TRIS-NPG

KW - in-situ Beobachtung

KW - geschichtete Strukturen

KW - peritectic solidification

KW - direct solidifcation

KW - layered structures

KW - transparent organic model systems

KW - thermo-solutal convection

KW - liquid channels

M3 - Master's Thesis

ER -