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. <br><br>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 vapor deposition of homogeneous or composite materials, (2) secondary fabrication, including shaping and microstructural control by operations such as mechanical working, machining, sintering, joining and heat treatment and (3) testing, which measures the degree of reliability of a processed part, destructively or non-destructively.