Periodical oscillating interface in directional growth under shear flow

Liquid-solid interface morphological evolution of SCN-2wt%H₂O alloy was investigated in the presence of shear flow. It has been found that shear flow strikingly enhances the stability of planar interface at lower pulling rates. In the intermediate range of pulling rate, the interface experiences periodical oscillating "planar-cellular" and "cellular-dendritic" growth patterns. The formation of oscillating growth modes can be explained by two reasons: (i) The stabilizing effect induced by shear flow competes with the growing destabilizing effect by the increase of pulling rate, which provides the driving force for morphological evolution; and (ii) the establishment of stable solute field at the liquid-solid interface needs a period of time, leading to the result that the interface evolution can not stay stable at the equilibrium state. However, as the puling rate becomes higher, it plays more and more important roles in pattern selection and dendritic growth forms.