  Solidification of alloys in a thermal gradient usually involves the
generation of flows by thermal or thermosolutal convection. We experimentally
study their effects on the dynamics of a solidification interface by inducing a
controlled sweeping flow in a directional solidification device. Flow is
induced in the sample from an external thermosiphon. Downstream inclination of
microstructures and downstream sidebranch development are observed. However,
the major outcome is the evidence of large scale travelling waves on the
solidification interface. They are induced by the coupling between
solidification and flow and yield repetitive striations of the solid phase. Two
waves are observed and characterized.
