About LSC

About LSC

Many kinds of materials such as metals and ceramics we use in our daily lives have complicated macro- and micro-structures that can not be easily imagined from their appearances, which is similar, for example, to that wood has grains, knots and growth rings. Structures of materials determine many properties of the materials. It is well known that even if two different alloys have a same chemical composition, they exhibit different material properties such as mechanical strength when they have different microstructures regarding the morphology and distribution of the precipitates or the grain size distribution of the matrix phase. In our research group, we study how to control the structure of materials, which leads to the control of the properties of materials.

The first structure of a material is formed when a solid is produced from vapor or liquid. The structure changes during cooling due to phase transformation, precipitation of new phases, deformation and recrystallization followed by grain growth. We study these changes in material structures experimentally and theoretically to apply the knowledge and new findings to develop new materials and processes.

 

 

 

 

Primer Class of LSC “A Wonderful World of Material Structures”

Observation of Structures
Let’s have a look at a macrostructure of an aluminum ingot cast into a cylindrical shape. The ingot was longitudinally sectioned, mounted in a resin, and polished using emery papers, but no structures can be seen at this moment.
 

After dipping the sample in an aqua regia (mixture of hydrochloric and nitric acids) for about 20 seconds, a pattern showing a columnar grain structure appeared.

This corrosive action by an acid to reveal metal structure is called etching. A large structure that can be seen by unaided eyes is called a macrostructure, while a small structure that can be seen using a microscope is called a microstructure.

 
Several Types of Structures
Dendrite
Dendrite is one of the most common solidification structures, and is formed in a shape like a tree having a trunk and branches when a crystal grows into liquid.
When an alumina tube was dipped into a super- cooled liquid aluminum, a dendritic crystal of aluminum grew from the surface of the alumina tube.
 
Solidification structure of a liquid film that have adhered on a crucible wall, showing a dendritic relief pattern.
 
Dendrites that have grown from the outer surface of a water-cooled cupper pipe dipped into an Al-Cu alloy liquid. When the cupper pipe was drawn up from the alloy liquid and then was rapidly rotated to drive away the liquid remaining in the depressions between dendrites using the centrifugal power, a dendritic structure appeared on the surface of the solidified alloy.