Evolution of dendritic patterns during alloy solidification: From the initial instability to the steady state.

The evolution of the crystal-melt interface was investigated during directional solidification of a dilute binary alloy, starting at the marginal stability time t(i) at which the planar interface first becomes unstable. The time delay between t(i) and the crossover time t(0) at which the interface modulation becomes observable was determined experimentally. The interface morphology was analyzed as the cellular pattern appeared, and it was followed through the coarsening phase to the final steady-state dendritic pattern. The relevance of the initial instability for steady-state pattern selection was verified experimentally, and some aspects of the coarsening dynamics were measured and compared with theoretical predictions of Warren and Langer [Warren, J. A. & Langer, J. S. (1990) Phys. Rev. A 42, 3518-3525; Warren, J. A. & Langer, J. S. (1993) Phys. Rev. E 47, 2702-2712].