MATERIALS SCIENCE 124
Mrs J.T. Kurasha
Course aim
• Students to understand the structure,
properties, capabilities and limitations of
engineering materials & selection process;
synthesis of suitable materials for different
applications.
Course objectives
1.
2.
3.
4.
Select suitable materials for various
engineering applications.
Analyse & test for the mechanical &
electrical properties of materials.
Study the structure of material
[crystalline & amorphous] & its
influence on the materials’ properties.
Understand the principles of phase
equilibria.
Course Content






Structure & properties of engineering materials
Common engineering materials
The chemistry & phase equilibria of engineering
materials.
Iron & steel – production and heat treatment
Corrosion theory of engineering materials
Materials testing.
Introduction to Materials Science
• Definition:
 It is the field of applied science concerned with inventing
new materials and improving existing ones, through
emphasis on underlying relationships between
composition, microstructure and properties of the
materials.
Fig 1.1: Materials science and
engineering tetrahedron
Historical perspective
• Materials are quite common & widespread, from
mundane household items to sophisticated
integrated circuits:
 Transportation
 Clothing
 Housing
 Communication
 Sanitation
 Recreation
 Industrial production, etc.
Cont’d
• Historically, the development and advancement of any society has been
intimately associated with its members’ ability to produce and manipulate
materials which meet their needs.
• Earliest humans had access only to materials that occur naturally, such as
clay, wood, stones, skins, etc.
• With time they discovered that heat treatment and addition of other
materials would produce materials with superior properties.
Figure 1.2 Early civilization periods according to material science development
Cont’d
• It is only in recent times that scientists have come to
understand the link between the structure of a material and
its properties.
• This knowledge has over the past 100 years allowed a massive
evolution in determining new material characteristics leading
to the development of 10s and 10s of thousands of new
materials (plastics, metals, glasses, fibres).
Thus Material Science involves investigating the relationship
between the structure and properties of materials.
Materials Engineering involves, on the basis of the said
relationship, designing or engineering the structure of a
material to produce a pre-determined set of properties.
Structure.
Relates to the arrangement of a material’s internal ,
subatomic components
Property.
All properties evoke a certain response when subject to
an external stimuli e.g. a polished surface shining, elastic
band stretching.
Properties of materials
• Solid materials have 6 main properties






Mechanical
Electrical
Thermal
Magnetic
Optical
Deteriorative
• The structure of a material depends on how it is processed. A
material’s performance is a function of its properties.
Figure 1.3 The four components in material science & their relationship.
Materials design and selection
Figure 1.4 Pictures of Coke in various containers. (Courtesy of the Coca-Cola Company)
Materials Design and selection
• The material designed for a specific application
should:
Have desired physical & mechanical properties
eg. desired strength & density for aeronautical
application will differ from hauling applications.
Be amenable to processing/manufacturing into
desired shape.
Provide an economical solution to the problem.
Environmentally friendly (preferably recyclable).
Classification of materials
• Solid materials fall into the following classes:
Metals and alloys
Ceramics
Polymers
Composites
Advanced materials.
Metals and alloys
•
Examples – Metallic elements Fe, Ni, Co, U, Au, Ag. Often occur
naturally as ores in association with non-metallic elements (C, N
and O).
The atom arrangement in metals &
alloys quite orderly.
Relatively dense
Stiff and strong
Ductile
Resistant to fracture
Good electrical & heat conductors (non-localized electrons)
Non- transparent to light
Some have magnetic properties (Fe, Co, Ni)

• Particularly used in structural and load bearing applications.
Ceramics



Compounds whose characteristics are in between metallic and
non-metallic elements. Frequently occur as oxides, nitrites and
carbonates, e.g Al2O3; SiO2; SiC; Si3N4.
Sand, rocks, clay minerals (porcelain), cement, glass are
examples of ceramics.
Ceramics are
Stiff & strong
Typically hard
Extremely brittle (lack of ductility)
Highly susceptible to fracture
Low electrical conductivity
New ceramics are being engineered to improve their resistance to fracture.
Examples include cookware, tiling, automobile engine parts.

Polymers
These are plastic and rubber materials.
•
Mainly organics based on carbon, hydrogen and other nonmetallic elements (O, N, Si)
•
Have a large chain-like, molecular structure often having a
backbone of C atoms
Polyethylene (PE)
Nylon
Poly vinyl chloride (PVC)
Polystyrene (PS)
Polymers have low densities, are not as stiff or as strong as metals.
They are chemically inert and unreactive. They have low
conductivities and soften/decompose at modest temperature.
•
Composites
•
•
•
•
•
•
The goal is to attain a combination of properties which supersedes any
of the properties of the individual materials by incorporating the best
characteristics of each of the component materials.
NATURAL composites - Wood and bone.
SYNTHETIC composites - Fibreglass & CFRP
FIBREGLASS -Glass fibre embedded within a polymeric material
(epoxy/polyester). Glass fibre is a material which is relatively strong &
stiff but brittle, while the polymer is more flexible.
Fibreglass has a low density and is relatively stiff, strong and flexible.
CARBON FIBRE –REINFORCED POLYMER (CFRP) - These are carbon
fibres embedded within a polymer. Are stronger and more stiff than
glass fibre but are more expensive. CFRP used in some aircraft &
aerospace applications and sporting equipments (eg bicycle parts, golf
clubs, tennis rackets, snowboards, skiis and automobile bumpers.)
Fibreglass
CFPR
Concrete
Advanced Materials
These are materials used for hi-tech applications, such as
(Electronic equipment; camcorders, CD, DVD & Blu ray players,
computers, fibre optics systems, spacecraft, aircraft, lasers, rockets,
integrated circuits, magnetic information storage, liquid crystal
display LCD)
•
Advanced materials are derived from either traditional materials
which have enhanced properties or from new highly developed,
high performance materials.
•
We will look at four categories of advanced materials
 Semiconductors
 Biomaterials
 Smart materials
 Nanomaterials
•
Semi-conductors
They exhibit intermediate electrical properties i.e.
those between conductors (metals & alloys) and insulators
(polymers & ceramics).
Their electrical characteristics are extremely sensitive to the
presence of small concentrations of ‘impurity’ atoms
Semi-conductors have ushered the advent of integrated
circuitry in the electronics industry
Biomaterials
Are used in components
implanted in the human body
to replace damaged body
parts.
They must be compatible with
body tissues and be non-toxic.
Metals, ceramics, polymers,
composites and semi-conductors
can all be used as biomaterials.
Smart materials
• This is a group of new, ‘state of the art’ materials that will
significantly influence future technological advances.
‘Smart’ implies that the materials are able to sense changes in
their environment and then evoke a predetermined response
to these changes. These are all traits which are inherent in living
organisms.
Components of a Smart System
Sensor. (Detects input).
Materials commonly used in fabricating sensors include optical
fibres, piezoelectrical materials and microelectromechanical
Systems (MEMS)
Cont’d
Actuator. (Performs the responsive and/or adaptive function). Can
change the shape, position, frequency or mechanical properties of a
material in response to changes in say temperature, pressure, humidity
etc.
Materials used as actuators include
 Shape-memory alloys (when deformed metals revert to original
shape when temperature is changed)
 Piezoelectric ceramics (expand/contract in response to an applied
electric field, conversely generate electric field when dimensions
changed)
 Magnetostrictive materials (analogous to piezoelectric materials but
in magnetic field)
 Electrorheological & Magnetorheological fluids (liquids whose
viscosity markedly changes when subject to electric/magnetic field)
Nanomaterials
This is a new class of materials which have tremendous
technological promise
 These can be from any of the four materials subgroups
(ceramics, metals, polymers and composites)
Unlike other materials, nanomaterials are distinguished not on the
basis of chemistry but on size
Nano (10-9 )
Prior to the advent of ‘nanotechnology’, scientist used the ‘top-down’
science approach in studying the physics & chemistry of materials ie
studying macro complex structures first, then subsequently investigating
the basic fundamental building blocks from which they were built.
• Advances in microscopy have enabled singular atoms & molecules to be
observed by the use of scanning probes
Cont’d



Thus it has now become possible to design & build new
structures from the atomic level ‘one atom or one molecule at a
time’.
‘Materials by design’
Atoms can thus be arranged in such a way as to impart certain
mechanical, electrical, magnetic & other properties. This is
called the ‘bottom-up’ approach & the study of these materials
is called ‘nanotechnology’.
Cont’d
•




Physical and chemical characteristics change drastically as
particle size approach atomic dimensions.
For instance some materials which are opaque at
macroscopic level become transparent at nanoscale
(copper)
Some solids become liquids
Inert materials become combustible
Insoluble matter becomes soluble
Cont’d
•
•


Nanoparticles are finding niches in biomedical, electronic,
sporting, energy and other industrial applications
However, the toxicological effects of these materials remain
largely unknown
Nanoparticles have extraordinarily high surface area to volume
ratios and hence may show high chemical reactivities.
High absorption rates into the body via skin, lungs, digestive
tract
Modern Needs in Materials Science
• Whilst tremendous progress has been made in material synthesis &
design, some challenges remain
 Developing even more specialized materials
 Considering the environmental effects of materials production.
Some applications where research is ongoing include
 Transportation. Weight of vehicles
Increasing engine operating temperature etc
 New & economic energy sources
 Materials in pollution control
 Most polymers are derived from non-renewable sources. Thus need
to discover new sources & develop new materials with comparable
properties and less adverse environmental impacts.
 Consider ‘cradle to grave’ lifecycle.
Summary check
Name the SIX property
classifications of materials.
Define ‘structure’ and
‘properties’ as these two
relate in material science.
Name three vital criteria
used in the material
selection process.
What four aspects are
considered in the design,
production and use of
materials?
What are the three basic
classes of materials?
Discuss ‘Advanced
Materials’.