At the heart of materials science is an understanding of the
microstructure of solids. "Microstructure" is used broadly in
reference to solids viewed at the subatomic (electronic) and
atomic levels, and the nature of the defects at these levels.
The microstructures of solids at various levels, especially the
defects, profoundly influence the mechanical, electronic,
chemical, and biological properties of solids. The
phenomenological and mechanistic relationships between the
microstructure and the macroscopic properties of solids are, in
essence, what the materials science is all about. This is best
represented by the "materials science triangle": synthesis-
microstructure-properties. Materials engineering, on the other
hand, is concerned with the design, fabrication, and testing of
engineering materials. Such materials must fulfill
simultaneously the dimensional properties, quality control, and
economic requirements. Several manufacturing steps may be
involved: (1) primary fabrication, such as solidification or