Maximal curvature and crystal orientation on directionally solidified dendrites

We experimentally address the locations of maximal curvature on crystalline cellular or dendritic interfaces that directionally grow in a thin sample of a transparent material. Local curvatures are determined on the whole dendrite tips by considering the intersection of nearby normals. It is found that, at the location of the curvature maximum, the interface normal points toward a particular direction solely set by the crystal lattice and equal in practice to the dendrite growth direction at large pulling velocity. This property is independent of the growth conditions (thermal gradient, velocity, dendrite spacing, and crystal orientation). It enables crystal orientations to be recovered from dendrite shapes and provides a bridge to understand the implications of anisotropy on the forms and orientations of directionally solidified dendrites.