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Material Science
Material science is an
interdisciplinary field involving the properties of matter and its applications
to various areas of science and engineering. Material science also deals
with properties and characteristics of materials.
What is a material?
Material is the thing of which something is
made, or something that consist of matter. Materials comprises of metals
and non-metals which must be operated upon to form the end product/desired
product.
Material classification
Most engineering materials are classified
into:
Metals – ferrous and non-ferrous
Organics
Composites
Ceramics
Semi-conductors – metalloids
(a) Metals
Metals play a major role in the industries and everyday life of human
beings. Metals from our chemistry are composed of elements which readily
give up electrons to produce a metallic bond and electrical conductivity.
Examples of metals are: iron, copper, aluminum, zinc and magnesium.
Metals generally possess the following characteristics
Lustre
Hardness
Low specific heat
Plastic deformability
Good thermal and electrical conductivity
Relatively high melting point
Strength
Ductility
Malleability
Opaquity
Stiffness
Rigidity
Formability
Machinability
Weldability
Castability
Dimensional stability
(b) Ceramic materials
Ceramics usually consist of oxide of nitrides, carbides, silicates or
borides of various metals. Ceramics materials contain compounds of
metallic and non metallic elements such as Mg0, S102,
SiC, glasses etc. Such compounds contain both ionic and
covalent bonds.
Examples of ceramic materials are: Refractoriness, insulators,
cement, glass, sand, brick, concrete and silicon carbide
The following are the characteristics of ceramics:
Brittleness
Rock-like
Resistance to high temperatures
Hardness
Abrasiveness
Insulation to flow of electric current
Corrosion resistance
Opaque to light
High temperature strength
(c) Organic materials – Non-metals
Organic materials from our chemistry mean materials that contain carbon
compounds. There are two major groups of organic/polymeric materials
namely, - natural and synthetic. Examples of organic materials are:
Plastics
Textiles
Rubber
Paper
Wood
Lubricants
Paints and finishes
Adhesive
Characteristics of organic materials are as
follows:
Light weight
Combustible
Soft
Ductile
Poor conductor of heat and electricity
Non dimensionally
Poor resistance to temperature
(d) Composite
Composites materials are materials that contain more than one material
type for example fibre glass in which glass fibres are embedded within a
polymeric material. Fibre glasses acquire its strength from the glass and
flexibility from the polymer. It has the characteristics of both
materials
(e) Semiconductors
Semiconductors materials are referred to as metalloids in chemistry, that
is element that are not metals or non-metals. Semiconductors have
electrical properties that are intermediate between the electrical conductors
and insulators.
f) Nano materials
Nano-materials are materials on a nanoscale 10-9 that has
novel properties. Nano materials are formed with the following methods –
thin film deposition, chemical vapour deposition and these materials are formed
by refining conventional materials.
1.3 Engineering Requirements of Materials
Engineering requirements of a material mean what is expected from the
material so that the same can be successfully used for making Engineering
components such as crankshaft, spanner etc.
When an Engineer thinks of deciding and fabricating an engineering part,
he goes in search of that material which possesses such properties that will
permit the component part to perform its functions successfully while in use.
The main engineering requirements of materials fall under three
categories
Fabrication requirements
Service requirements
Economic requirements
1.3.1 Fabric ability requirements - means that the material should
be ale to get shaped (e.g. cast, forged, formed, machined, sintered etc) and
joined (e.g. welded, brazed etc) easily. Fabrication requirements relate
themselves with materials machinability, ductility, castability,
heat-treatability, weldability etc
1.3.2 Service requirements – means that the material selected for
the purpose must stand up to service demands e.g. proper strength wear
resistance, corrosion resistance, etc.
1.3.3 Economic requirements – means that the engineering part
should be made with minimum overall cost. Minimum overall cost may be
achieved by proper selection of both technical and marketing variables.
2.0 Properties of Engineering Materials
Material property is a factor that influences quantitatively or
qualitatively the response of a given material to imposed stimuli and
constraints for example forces temperatures and environments. Properties
of a material define its suitability for a particular use in industry.
In principle all material properties have a statistical behavior.
The following below are the different material properties:
Mechanical properties (b)Thermal properties
(c) Electrical properties (d)Magnetic properties
(e) Chemical properties (f) Optical properties
(g) Physical properties (h)Technological properties
2.2
Mechanical Properties
Mechanical properties of material are the term that describes the
behavior of the material under the action of external forces that is applied
forces and loads. Material response of materials to applied forces will
depend on the type of bonding, the structural arrangement of atoms or molecules
and the type and number of imperfections. The following are the various
mechanical properties:
2.2.1
Elasticity
The ability of a loaded material to return to its original shape after
unloading. Loading a solid thus affects its dimensions but the resulting
deformation will disappear upon unloading.
2.2.2
Plasticity
• The property of a material by virtue of which is permanently deformed
when it has been subjected to an externally applied force great enough to
exceed the elastic limit.
3.3.3
Toughness
• Toughness – it is the property of a material to resist fracture due to
high impact loads like hammer blows. It is the ability of a material to
resist load beyond plastic deformation up to fracture.
3.3.4
Resilience
• Resilience is closely related to toughness. It is the ability of a
material to resist shock and impact loads. The ability of a material to
deformed elastically and recovered upon unloading.
3.3.5
Tensile strength
• Tensile strength is a measure of the strength and ductility of a
material. It is a ratio of the maximum load to original cross-sectional
area.
3.3.6
Yield strength
• The ability of material to resist plastic deformation is called the yield
strength and is calculated by dividing the force initiating the yield by the
original cross sectional area of the specimen.
3.3.7
Impact strength
• It us the ability of a material to resist or absorb shock energy before
it fractures. It depends on the structure of the material.
3.3.8
Ductility
• Ductility refers to the ability of a material to undergo deformation
under tension without rupture. Ductility is the ability of a material to
be drawn.
3.3.9
Malleability
• Malleability is the ability of a material to withstand deformation under
compression without rupture. The property of a metal which makes it
possible for it to be formed by hammering or rolling. Malleability is
compressive property while ductility is tensile
3.3.10
Fatigue
• Fatigue is a kind of failure that occurred as a result of fluctuating or
dynamic loading being imposed on a machine element. The said machine
element fails below the tensile strength for that material. The failure
is progressive, beginning as minute cracks that grow under the action of
fluctuating stresses whose maximum value is less than the tensile strength of
the material. It is the most catastrophic failure that materials
experience in operations
3.3.11
Hardness
• Hardness is the resistance of material to plastic deformation usually by
indentation. However, the term may refer to stiffness or temper or to
resist scratching. The hardness of a material depends on the type of
bonding forces between atoms ions or molecules
3.3.12
Brittleness
• Brittleness is defined as a tendency to fracture without appreciable
deformation and is the opposite of Ductility or malleability
3.3.13
Wear Resistance
• Wear is the unintentional removal of solid material from rubbing
surfaces. The ability of a material to resist wear and abrasion.
There are two types of wear namely – Adhesive wear, referred to as galling,
scuffing or scoring. This is characterized by an intensive interaction
between two bearing surfaces resulting from mutual adhesion of the metals at
the junction.
• Abrasive wear – it is the removal by plowing or gouging out from the
surface of material by another body much harder than the abraded surface.
3.3.14
Creep
• Creep is the failure that occurs to a material that is used at an
elevated temperature and a constant loading. For metals, creep becomes
important at temperature greater than about 0.4Tm (Tm =
absolute melting temperature) for lead is less than room temperature. It
is a progressive phenomenon.
• 3.4 Factors affecting Mechanical Properties
• Mechanical properties are those which define the behavior of a material
under applied loads. The following are the factors:
• Alloy contents such as addition of w, cr etc improve hardness
and strength of materials.
• Grain size – It is either fine or coarse the fine grams here higher
strength.
• Crystal imperfections such as dislocations reduce the strength of the
material
• Manufacturing defects – such as cracks, blowholes etc
• Excessive cold working produces strain – hardening and the material may
crack.
• Factors affecting mechanical properties.
• Mechanical properties are those properties which define the behavior of a
material under applied loads.
• The following affect the properties are.
• (1) Alloy contents such as W, Cr, etc. improve hardness and strength of
materials.
• (2) Fine grain size materials exhibit higher strengths and vice
versa.
• (3) Crystal imperfections such as dislocations reduce the strength of the
materials.
• (4) Excessive cold working produces strain hardening and the material may
crack.
• (5) Manufacturing defects such as cracks, blowholes etc. reduce the
strength of the material
• EFFECT OF GRAIN SIZE ON PROPERTIES OF METALS.
• On the basis of grain sizes materials are classified into two namely.
• (a) fine grain materials, (the grain size is small
).
• (b) coarse grain materials (the grain size is large).
• Grain size is very important in deciding the properties of
polycrystalline materials because it affects the are and length of the grain
sizes on the mechanical properties of metals.
• (1) Fine grained materials possess higher strength, toughness,
hardness, and resistance to suddenly applied force.
• (2) Fine grained materials possess bitter fatigue resistance and high
impact strength.
• (3) Fine grained materials are more crack resistance and prove to be
better finish in deep drawing unlike coarse grained materials which give rise
to orange peel effect.
• (4) Fine grained materials generally exhibit higher strength, the coarse
grained material at low temperature while at high temperature the reverse is
the case.
• (5) Coarse grained materials has better creep strength than fine grained
materials at elevated temperature .
• (6) Coarse grained material possesses.
• EFFECT OF HEAT TREATMENT ON PROPERTIES OF METALS.
• Heat treatment is an operation which involves heating and cooling of a
metals to obtain desirable.
• (1)Hardness and strengthens the metal .
• (2)Improves machinability.
• (3)Softens metal for further working as in wiredrawing.
• Improves ductility and toughness.
• Homogenizes the metal structure.
• Improves thermal properties such as conductivity.
• Relieves internal stresses developed in metals, alloys during welding,
cold working casting and forging etc.
• Produces a hard wear resistant surface on a ductile steel piece.
• Improves electrical and magnetic properties.
• Increases resistance of materials to heat, wear, shock and corrosion.
• Effect of Atmospheric Exposure on Properties of Metals.
• The atmosphere contains mainly nitrogen and oxygen and other gaseous
product such as sulphurdioxide, hydrogensulphide, moisture,etc. As industrial
and other pollutants.
• On account of oxygen, an oxide film forms on the metals.
• (i)In the presence of humid air, an oxide film rust can be seen on the
surface of mild steel which is not desirable.
• The oxide film on the metal surface absorbs moisture, due to development
of cracks or discontinuities on the oxide film, local cell formation takes
place providing a fresh exposure of metal to the action of humid
atmosphere.
• A flow of local corrosion current between anodic areas of newly exposed
metal surface and the large cathode areas of the coated. Metal takes place
resulting in corrosion of the exposed surface.
• )The oxide film formed on aluminum, nickel, chromium or stainless steel
acts as a protective coating and resist further oxidation. Stainless steel
douse not rust because of the presence of chromium oxide film. Though in
industrialized areas in the presence of reducing agents, the surfaces of the
above metals become tarnished.
• a: When exposed to moist ( and saline) atmosphere the metals may corrode.
• Corrosion is a gradual chemical attack on a metal under the influence of
a moist atmosphere, (or of a natural or artificial solution). Aluminum
fins of the condenser of an air conditioner corrode when the air
conditioner is used in coastal areas. Corrosion adversely affects the
life and performance of a component in service.
• b: When exposed to very cold atmosphere, even ductile metals may behave
like brittle metals.
• Water pipes in very cold countries do burst as a result of the
atmospheric conditions.
• C: When the metal are subjected to a very hot atmosphere there
is
• creep
• Grain boundary weakening
• Change of conventional properties.
• Allotropic and other phase changes
• Reduction in tensile strength and yield point.
• Accelerated oxidation and or corrosion.
• EFFECT OF LOW TEMPERATURE ON THE PROPERTIES OF METALS
• -cryogenics is the study of the behavior of matter at temperatures below
-200 the example of low temperatures environments are food processing,
liquefaction of gases, synthetic rubber manufacture, hydrocarbon
polymerization, high altitude aircrafts(-50℃),refrigerator
applications(-60℃),dewaxing of petroleum(-100℃) ships travelling in cold
waters. the low temperatures affect the properties of metals in the following
ways.
• As the temperature lowers, there is an increase in yield strength,
tensile strength modulus and hardness and a decrease in ductility.
• At lower temperatures, a ductility material becomes brittle.
• Creep strength improves at low temperatures.
• No changes in the microstructure of a material as the temperature is lowered.
• Metals such as aluminum, zinc, tin, and lead show phenomenon
of super
• conductivity at lower temperatures (within a few degrees of absolute zero
temperature).
• (vi) FCC metals and alloys retain their ductility substantially
unimpaired up to 240℃
• (vii) Copper, aluminum ,nickel and austenitic alloys retain their much of
tensile, ductility and resistance to shock at low temperatures in
spite of the increase in strength.
• ELECTRICAL PROPERTIES.
• One of the significant characteristics of the materials is their ability
to permit or resist the flow of electricity. Materials to be used in electrical
equipments can be selected on the basis of their electrical properties such as
• Resistivity
• Conductivity
• Temperature coefficient of resistance.
• Dielectric strength
• Thermoelectricity
• Other electrical properties.
• Resistivity: is a characteristic properties of the materials from which
the conductor is made.
• Resistivity π =R.A/L
• R= resistance (ohms) of a conductor
• A= area of the conductor
• π= ohms cm or m.
• Resistivity is that electrical property of a material with which it
implies or resist the flow of electricity through it.
• Conductivity electrical conductivity is that electrical property of a
material with which it allow the passage of electric current through the
material
• ; i.e. the material provides on easy path for the flow of electricity
though it. Electrical conductivity permits the movement of electrical charge
from one location to another.
• Π± = 1/ π =1/RA.
• Note: unit of Π± are ohm-1cm-1 (mhos/cm).
• Charge may be carried by ions or electrons in ionic conductivity, the
carries are electrons or electrons holes.
• Conductivity, Π± = nqΒ΅.
• n = is the number of charge carriers in a material.
• q = charge carried by each.
• Β΅. = mobility of the carriers.
• Band model of conductivity.
• Conductivities of metals (conductors), semi conductors and insulators
differ much
• from each other´s, for example – silver 0.6×108 ohm-1m-1conductor.
• A good insulator =10-16
• A semi conductor=2×10-2
• High conductivity in metals is associated with the presence of free or
conduction electrons.
• Valency level in the free atom, in solid metals, they are pooled and they
occupied a band or zone of extremely closed values.
• Conductor – metals with one, two or three valency electrons are
conductors because they have unfilled valency bands.
• Semi conductors – such as selenium, zinc, sulphide, Germanium, and
silicon etc. are characterized by filled valence band, but only a narrow forbidden
range exist between the filled valence band and empty band. The application of
thermal energy in such cases excites electrons across the forbidden zone into
the empty higher band, where the exited electrons are available for conductions
• Insulators. - The valence band is completely filled,
that there is no overlapping of bands and wide forbidden rang, extremely high
electrical fields would be required to bring electrons to the empty band.
Though, with high energy insulator can be made to conduct.
• Temperature coefficient of resistance.
• Temperature coefficient of resistance is usually employed to
specify the variation of resistivity π with temperature. Π±T
= π- πo / πo
• Π±T = 1/T – TO.
• π= resistivity at temperature T
• πo= resistivity at temperature TO
• Dielectric strength
• Dielectric strength means the insulating capacity of a material against
high voltages. A material having high dielectric strength can withstand
sufficient high voltage field across it before it will breakdown and conduct. A
dielectric is an electric insulator.
• Dielectric strength of
• (i)Alumina of a spark plug body range from 50-400voit per mil
thickness
• Freon’s(refrigerant) is over 400voits per mil thickness.
• Thermoelectricity
• (Thermoelectricity effect forms the
basis of the thermocouple operation. if two dissimilar metals are joined and
this junction is then heated; a small voltage in the milivolt range is produced
and this is known as the thermoelectric effect.
• other electrical properties of materials are
• (a)electrochemical phenomenon(as a storage batteries)
• (b)Physical effects (as in contact potentials)
• (c )Mechanical effects(as in radars)
• MAGNETIC PROPERTIES
• The study of magnetic properties become necessary because the science of
magnetism explain many aspects of the structure and behavior of matter. The
following are the examples
• permeability
• coercive force
• hysteresis
• super conductivity
• PERMEABILITY
• Permeability—magnetic permeability measures the
relative case with which magnetism may be developed in a material.
• Β΅=B/H,B=magnetic induction,
• H=intensity
of magnetizing field,
• Β΅=magnetic
permeability, the large the value of Β΅,the smaller is the magnetizing force H
necessary to produce
• a given magnetization B.A vacuum is assigned permeability of
1,paramagnetic materials have a permeability greater than 1 where as
diamagnetic materials have a permeability less than 1 while some common
ferromagnetic steels have permeability up to about 20,000.
• (i) Coercive force-this is the opposing magnetizing force which is
necessary to remove previous magnetization or residual magnetization.
• Superconductivity-is a phenomenon referring to the stable at which
the abrupt drop in electrical resistance of certain materials becomes zero at
temperatures below a certain critical temperature TC.
• A Superconductor becomes a perfect diamagnetic material excluding a
magnetic field except in a small penetration region near the surface extending
over a region about 50nm deep, this is known as Meissonier effect.
• Hysteresis- can be define as the lag in the changes of
magnetization behind variations of
• The magnetic, if a ferromagnetic materials is subjected to increasing or
decreasing magnetic field changes in the magnetic induction plotted against the
magnetic fields result in a hysteresis loop on increasing the magnetizing field
H, the magnetizing induction B, will also increase and the magnetization curve
will follow line OB.
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