Volume 87, Number 4, August 2009
Article Number 40007
Number of page(s) 6
Section General
Published online 15 September 2009
EPL, 87 (2009) 40007
DOI: 10.1209/0295-5075/87/40007

Evidence of the transition from ordered to disordered growth during rapid solidification of an intermetallic phase

H. Hartmann1, 2, D. Holland-Moritz1, P. K. Galenko1, 2 and D. M. Herlach1

1   Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR) 51170 Köln, Germany, EU
2   Institut für Experimentalphysik IV, Ruhr-Universität - 44780 Bochum, Germany, EU

received 19 May 2009; accepted in final form 13 August 2009; published August 2009
published online 15 September 2009

The dendrite growth velocity during solidification is measured on liquid drops of the intermetallic compound ${\rm Ni}_{50}{\rm Al}_{50}$ undercooled by levitation up to 265 K. A sharp increase of the growth velocity is found at a critical undercooling $\Delta T^{*}\approx 250\,{\rm K}$. In situ diffraction of synchrotron radiation on levitation-processed samples unambiguously shows a transition from ordered to disordered growth at $\Delta T^{*}$. The sharp interface model is extended to describe the transition from ordered to disordered dendrite growth by taking into account the velocity dependence of the order parameter and the kinetic growth coefficient.

05.70.Fh - Phase transitions: general studies.
81.10.-h - Methods of crystal growth; physics of crystal growth.
61.05.C- - X-ray diffraction and scattering.

© EPLA 2009