Callister_-_Materials_Science_and_Engineering_-_An_Introduction_7e_(Wiley,_2

MATERIALS SCIENCE AND ENGINEERING
     It's useful to subdivide the discipline of materials science and engi￾neering into materials science and materials engineering subdisciplines. Strictly
speaking, “materials science” involves investigating the relationships that exist
between the structures and properties of materials. In contrast, “materials engi￾neering” is, on the basis of these structure–property correlations, designing or en￾gineering the structure of a material to produce a predetermined set of properties.2
From a functional perspective, the role of a materials scientist is to develop or syn￾thesize new materials, whereas a materials engineer is called upon to create new
products or systems using existing materials, and/or to develop techniques for pro￾cessing materials. Most graduates in materials programs are trained to be both
materials scientists and materials engineers.
“Structure” is at this point a nebulous term that deserves some explanation. In
brief, the structure of a material usually relates to the arrangement of its internal
components. Subatomic structure involves electrons within the individual atoms and
interactions with their nuclei. On an atomic level, structure encompasses the or￾ganization of atoms or molecules relative to one another. The next larger structural
realm, which contains large groups of atoms that are normally agglomerated to￾gether, is termed “microscopic,” meaning that which is subject to direct observation
using some type of microscope. Finally, structural elements that may be viewed with
the naked eye are termed “macroscopic.”
The notion of “property” deserves elaboration. While in service use, all mate￾rials are exposed to external stimuli that evoke some type of response. For exam￾ple, a specimen subjected to forces will experience deformation, or a polished metal
surface will reflect light. A property is a material trait in terms of the kind and mag￾nitude of response to a specific imposed stimulus. Generally, definitions of proper￾ties are made independent of material shape and size.
Virtually all important properties of solid materials may be grouped into six dif￾ferent categories: mechanical, electrical, thermal, magnetic, optical, and deteriorative.
For each there is a characteristic type of stimulus capable of provoking different re￾sponses. Mechanical properties relate deformation to an applied load or force; exam￾ples include elastic modulus and strength. For electrical properties, such as electrical
conductivity and dielectric constant, the stimulus is an electric field. The thermal be￾havior of solids can be represented in terms of heat capacity and thermal conductiv￾ity. Magnetic properties demonstrate the response of a material to the application of
a magnetic field. For optical properties, the stimulus is electromagnetic or light radia￾tion; index of refraction and reflectivity are representative optical properties. Finally,
deteriorative characteristics relate to the chemical reactivity of materials.The chapters
that follow discuss properties that fall within each of these six classifications.
In addition to structure and properties, two other important components are
involved in the science and engineering of materials—namely, “processing” and
“performance.”With regard to the relationships of these four components, the struc￾ture of a material will depend on how it is processed. Furthermore, a material’s per￾formance will be a function of its properties. Thus, the interrelationship between
processing, structure, properties, and performance is as depicted in the schematic
illustration shown in Figure 1.1. Throughout this text we draw attention to the


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