Directional cellular growth of succinonitrile-0.075 wt% acetone bulk samples Part 1: Results of space experiments

Interface pattern evolution during directional solidification has been inve stigated in the microgravity environment of a space shuttle mission providi ng diffusive conditions for cellular pattern evolution. A model transparent alloy of succinonitrile-acetone was used in these studies for in situ obse rvation of the dynamic process of pattern evolution. In addition to the mic rogravity environment, alloy composition and growth condition experiment pa rameters were selected in such a way that the planar-to-cellular transition was supercritical, and pattern evolution was examined dose to the transiti on velocity that gave rise to very small amplitude cells. Since the supercr itical transition shows continuous increase in amplitude with velocity, non -linear effects in wavelength selection are small. This means that linear t heory could be used to interpret the results. The evolution of primary spac ing and the order of cellular arrangements were characterized as a function of time for three different velocities. No sharp wavelength selection in p rimary spacing was observed in the experimental results, and the distributi on of steady-state spacing was characterized for each velocity. Wavelength selection for supercritical transition near the transition point can also b e explained by stability analysis. (C) 2001 Elsevier Science B.V. All right s reserved.