Kinetics of dendrite growth and dendritic fragmentation in the undercooled Co_81.2 Cu_18.8 alloy’s melt

¹ Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät, Löbdergraben 32, 07743 Jena, Germany
e-mail: PeterGalenko@uni-jena.de
² Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 51147 Köln, Germany
³ Institut für Festkörperphysik, Ruhr-Universität Bochum, 44780 Bochum, Germany

Received: 30 December 2013
Accepted: 4 April 2014

Abstract

The growth velocity during solidification of an undercooled melt of a Co-Cu alloy processed by electromagnetic levitation was measured using a high speed video camera. Applying a model of local non-equilibrium solidification, theoretical predictions of dendrite growth velocity and dendritic growth radii are compared with high-accuracy measurements of the growth kinetics. As the undercooling ΔT reaches a critical value consistent with the dendrite growth velocity being equal to the atomic diffusion speed V_D in bulk liquid, ΔT = ΔT(V_D), the velocity-undercooling relationship exhibits a break-point. A distinct change in the dendritic growth mechanism exists with the onset of complete solute trapping and chemically partitionless solidification of the core of the main stems of the dendrites occurs. A complete transition to the thermally controlled growth of dendrites occurs at ΔT = ΔT(V_D) that leads to essential changes in the microstructure of dendritic patterns The phenomenon of dendritic fragmentation in Co-Cu melts, solidifying at ΔT < ΔT(V_D), is discussed.