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 di rectional solidification of a dilute binary alloy, starting at the mar ginal stability time ti at which the planar interface first becomes un stable. The time delay between ti and the crossover time to at which t he interface modulation becomes observable was determined experimental ly, The interface morphology was analyzed as the cellular pattern appe ared, and it was followed through the coarsening phase to the final st eady-state dendritic pattern, The relevance of the initial instability for steady-state pattern selection was verified experimentally, and s ome 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].