Cellular pattern dynamics on a concave interface in three-dimensional alloy solidification.

Three-dimensional interface patterns are common in condensed matter, whose dynamical behavior is still deserving clarification. The dynamics of cellular patterns formed at the concave solid-liquid interface during directional solidification in a cylinder of a transparent alloy is studied by means of bright-field live imaging. For each pulling velocity, in situ observation shows that the asymptotic cellular pattern, which establishes with time, is characterized by the continuous birth of a large number of cells at a circular source of morphological instability on the periphery, the sustained collective gliding of the whole cellular array down the interface slope, and the elimination of coarse cells at the central sink. This very peculiar dynamics is the specific signature of the cell advection imposed by interface curvature for the concave situation in three-dimensional solidification. It follows from the comparison between experimental cell gliding and pure slope advection that an additional mechanism of pattern advection is active. It is attributed to fluid flow interaction, estimated on the basis of the Forth and Wheeler traveling wave equations.