MATERIALS SCIENCE AND ENGINEERING

Sometimes it is 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.

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

relationships among these four components in terms of the design, production, and
utilization of materials.
We now present an example of these


processing -structure -properties -performance


principles with Figure 1.2, a photograph showing three thin disk specimens placed
over some printed matter. It is obvious that the optical properties (i.e., the light
transmittance) of each of the three materials are different; the one on the left is trans-
parent (i.e., virtually all of the reflected light passes through it), whereas the disks in
the center and on the right are, respectively, translucent and opaque.All of these spec-
imens are of the same material, aluminum oxide, but the leftmost one is what we call
a single crystal—that is, it is highly perfect—which gives rise to its transparency. The
center one is composed of numerous and very small single crystals that are all con-
nected; the boundaries between these small crystals scatter a portion of the light re-
flected from the printed page,which makes this material optically translucent. Finally,
the specimen on the right is composed not only of many small, interconnected crys-
tals, but also of a large number of very small pores or void spaces. These pores also
effectively scatter the reflected light and render this material opaque.
Processing Structure Properties Performance
Figure 1.1 The four components of the discipline of materials science and
engineering and their interrelationship.

Materials science is an interdisciplinary field involving the properties of matter and its applications to various areas of science and engineering. This science investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It includes elements of applied physics and chemistry. With significant media attention focused on nanoscience and nanotechnology in recent years, materials science has been propelled to the forefront at many universities. It is also an important part of forensic engineering and failure analysis. Materials science also deals with fundamental properties and characteristics of materials.