Microstructure is the very small scale structure of a material, defined as
the structure of a prepared surface of material as revealed by an optical
microscope above 25× magnification. The microstructure of a material (such as
metals, polymers, ceramics or composites) can strongly influence physical
properties such as strength, toughness, ductility, hardness, corrosion
resistance, high/low temperature behaviour or wear resistance. These
properties in turn govern the application of these materials in industrial
practice.
Microstructure at scales smaller than can be viewed with optical microscopes
is often called nanostructure, while the structure in which individual atoms
are arranged is known as crystal structure.