Berlin 2005 – wissenschaftliches Programm

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M: Metallphysik

M 14: Wachstum

M 14.3: Vortrag

Freitag, 4. März 2005, 15:15–15:30, TU H2038

Dendritic structure and solidification kinetics of undercooled Ni-Zr alloys — •Peter Galenko, Dieter Herlach, Gandham Phanikumar, and Oliver Funke — Intitut fuer Raumsimulation, DLR, 51170 Koeln, Deutschland

Ni-Zr droplets have been melted and undercooled in electromagnetic levitation facility. After controlled triggering of solidification, measurements of solidification velocity have been provided by capacity sensor technique and high-speed camera technique. Novel experimental results on the kinetics of solidification of undercooled Ni-Zr alloys are found. The velocity-undercooling relationship have been plotted for three contents of diluted Ni-Zr alloys and metallographic investigations of a crystalline structure have been performed. The microstructure of all samples is found to be a dendritic like. The microstructural features as a function of undercooling are attributed to morphological transitions, viz., from grain refined (GR) equiaxed microstructure to a coarse grained (CG) dendritic microstructure and to a grain refined (GR) equiaxed microstructure. The kinetics of dendritic growth in undercooled droplets are analysed using the local nonequilibrium solidification model [1]. The experimental values of critical undercoolings for the GR-CG-GR transitions are compared with the modeling predictions. The disagreement of the theoretical predictions are attributed to the influence of convective flow, especially, at small and moderate undercoolings.

The work was supported by DFG under contract No. He 1601/13.

[1] P.K. Galenko and D.A. Danilov, Phys. Lett. A 235 (1997) 271; J. Cryst. Growth 197 (1999) 992.