Prof. Selvamanickam's Research Group
Solidification processing - Zone melting, Crystal growth and top-seeded melt-textured growth of grain-aligned ceramics

Crystal growth and directional solidification processes enable synthesis of single crystals and microstructures with columnar grains with minimum number of grain boundaries perpendicular to the growth direction. Bridgman and Zone melting & recrystallization (ZMR) are two directional solidification processes being used. Zone melting and recrystallization (ZMR) enables controlled melting and solidification of a narrow zone at high temperature gradients.

A top-seeded melt-textured growth process is used to grow large grain-aligned structures of even incongruent melting compounds without a temperature gradient. This technique is schematically shown in the following figure. The sample is partial melted with a short excursion in temperature above its melting point. A single crystalline or a melt-textured seed of a material with a melting point above this temperature, and with a same crystallographic structure, and lattice parameters close to that of the sample is used. Nucleation is initiated from the top of the partially-melted sample as it is cooled down to the vicinity of its solidification temperature. By slow cooling through the solidification temperature or holding at an undercooled temperature, growth of crystallites with grains aligned along the basal plane proceeds laterally and vertically with an epitaxial relationship from the seed.

Essentially, the crystallographic orientation of the seed material is reproduced from a size of a few millimeters to about 10 cm in the melt-textured bulk material. Since the basal planes of the melt-textured material are aligned over the entire bulk, materials with anisotropic properties can be fabricated.

We are exploring various solidification techniques, especially top-seeded melt-textured growth and zone melting and recrystallization for highly grain-aligned microstructures of complex materials.

Top-seeded melt-textured growth process to fabricate highly grain-aligned bulk materials