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AD-302 MATERIALS SCIENCE AND ENGINEERING M IE SE TION
Chapter 01Introduction to Engineering Materials1.0
IntroductionMaterial science and engineering is interdisciplinary
areaconcerned with invention of new materials and improving
thealready known and existing materials for their better use in
presentscenario. Engineers in all disciplines should have some
basic andapplied knowledge of engineering materials so. that they
will beable to do their work more effectively when using them. A
vastrange of materials is available to the engineer and all
thesematerials possess widely different properties. Glass,
concrete,rubber, timber, metals, alloy, plastic or ceramics are all
used byengineers, but their characteristics and properties are
completelydifferent from each other. All engineers are concerned
with theoptimum use of materials and they have to select the most
suitablematerial for their job. The material can be for civil
engineeringstructure, electrical transmission, power plant, modem
cuttingmachines or perhaps an electric component.The term materials
science and engineering combines bothmaterials science and
engineering materials. Materials science isprimarily concerned with
the search for basic knowledge about theinternal structure,
properties, and processing of materials.Materials engineering is
mainly concerned with the use offundamental and applied knowledge
of materials.New materials with special properties are constantly
beingdiscovered and developed, and thus materials science
andengineering is a continually expanding field.1.1 Types of
Materials
Engineering materials are divided into three main
classes'metallic materials, ceramic materials and polymeric
materials.In addition to the three main classes of materials two
processing orapplication classes, composite materials and
electronicmaterials, because of their great engineering
importance.1.1.1 Metallic Materials
The study metallic materials constitute a major division ofthe
materials science and engineering field. In general,
metallicmaterials are inorganic substances composed of one or
moremetallic elements, but they may also contain
nonmetallicelements. Most metals have a crystalline structure of
closelypacked atom arranged in an orderly manner. Metals in general
aregood electrical and thermal conductors. Many are relatively
strongat room temperature and retain good strength at
elevatedtemperature. Metals are commonly alloyed together in the
liquidstate so that, upon solidification, new solid metallic
structures withdifferent properties can be produced. Metals and
alloys are oftencast into the nearly final shape in which they will
be used andthese products are called castings. However, most metals
andalloys are first cast into shapes such as sheet ingot or
extrusionbillets, which are subsequently worked by processes such
asrolling and extrusion into wrought products, for example,
sheet,plate, and extrusion.Metals and alloys can be classified into
ferrous andnonferrous groups. Ferrous metals and alloys contain
iron as theirmajor metallic element; example of ferrous alloys is
the steels andcast irons. Nonferrous metals and alloys contain
element otherthan iron as their major metallic element; example of
nonferrousmetals and alloys have innumerable applications, such as
low-carbon sheet steels for appliances and auto bodies, stainless
steelsfor cutlery and utensils, aluminum alloys for aircraft frames
andsurfaces, and unalloyed copper for electrical wiring and
waterpipes.1.1.2 Ceramic Materials
The study of ceramic materials forms a second majordivision of
the field of materials science and engineering.
Ceramics are inorganic materials consisting of metallic
andnonmetallic element chemically bonded together. They can
becrystalline, noncrystalline, or mixtures of both. Most
ceramicmaterials have high hardness, high-temperature strength, and
goodchemical resistance; however, they tend to be brittle. Ceramics
ingeneral have low electrical and thermal conductivities.
Whichmakes them useful for electrical and thermal
insulativeapplications? Most ceramic materials can be classified
into threegroup traditional ceramic, technical ceramics, and
glasses.Traditional CeramicsThese consist of three basic components
clay, silica, andfeldspar. The clay provides the workability of the
ceramic beforeit is hardened by the firing process. Clay makes up
the major bodymaterials; it consists mainly of hydrated aluminum
silicates (Ah03Si02 H20) with smaller amounts of other oxide
impurities. Thesilica (Si02) has a high melting temperature and
provides therefractory component of traditional ceramics. The third
componentfeldspar (k20 Al203 6H20) has a low melting temperature
andproduces a glass when the ceramic mix is fired; it bonds
therefractory components together. Traditional ceramic
productsfabricated from whiteware such as electrical porcelain and
sanitaryware are made from components of clay, silica, and feldspar
forwhich the composition is controlled.Technical ceramicsAlso known
as advanced ceramics, technical ceramics arebased on pure or nearly
pure ceramic components alone or incombination. The raw materials
for technical ceramics must beprocessed carefully so that a
controlled product can be produced,and they are made by using
various composition mixes andprocessing procedures. Example of
technical ceramics isaluminum oxide (AI03), zirconia (Zr03),
silicon carbide (SiC),silicon nitride (SbN4 and barium titanate
(BaTi03). Applicationfor technical ceramics include alurninas for
auto spark-pluginsulators and substrates for electronic circuitry,
dielectricmaterials fur capacitors. Ceramic tool bits for
machining, andhigh-performance ball bearings.GlassGlasses differ
from the other ceramic materials in that theirconstituents are
heated to fusion and then cooled to a rigid statewithout
crystallization. A characteristic of a glass is that it has
anoncrystalline structure with no long-range order. Most
inorganicglasses are based on the glass forming silicon oxide,
silica (Si02).About 90 of the produced is soda-lime glass which has
the basiccomposition of 71-73 Si (h, 12-14 sodium oxide (Na20).
and10-12 calcium oxide (CaO). The sodium oxide and are added
tolower the viscosity of tile glass so that it becomes easier to
work.Soda-lime glass is used, for example, for flat glass,
containers, andlight products, where high chemical durability and
heat resistanceare not required. Many other types of glasses with
differentcompositions are produced for special
applications.1.1.3Polymeric Materials
The study of polymeric materials forms a third majordivision of
materials science and engineering. Most of thesematerials consist
of carbon-containing long molecular chains ornetworks. Structurally
most of them are noncrystalline, but someare partly crystalline.
The strength and ductility of polymericmaterials vary greatly. Most
polymers have low densities andrelatively low softening or
decomposition temperatures. Many aregood thermal and electrical
insulators. Polymeric materials havereplaced metals and glasses
formany applications.Most polymeric materials can be classified
asthermoplastics, thermosets, or elastomers.Thermoplastics
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