Spatial Period-Doubling Instability of Dendritic Arrays in Directional Solidification

Abstract

A directional solidification study of succinonitrile doped with coumarin 152 was performed in which the pulling speed $V_P$ was gradually reduced in small steps. A spatial period-doubling instability was observed when $V_P$ reached $17.4\mu \mathrm{m}/\mathrm{s}$, in good quantitative agreement with the prediction of Warren and Langer [Phys. Rev. A 42, 3518 (1990)]. This experiment, in conjunction with two previous studies, conclusively demonstrates the absence of a dynamical selection mechanism for the interdendritic spacing ${\lambda }_1$.