Materials for Engineering 20ME11T DTE Karnataka C-20 syllabus

Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 1
Materials for Engineering [20ME11T]
Unit I- Notes
1.1 Classification of Engineering Material
Basically Engineering Materials can be classified into two categories-
1. Metals
2. Non-Metals
Metals are polycrystalline bodies which are having number of differentially oriented fine
crystals. Normally major metals are in solid states at normal temperature. However, some metals
such as mercury are also in liquid state at normal temperature. All metals are having high
thermal and electrical conductivity. All metals are having positive temperature coefficient of
resistance, Means resistance of metals increases with increase in temperature. Examples of
metals – Silver, Copper, Gold, Aluminum, Iron, Zinc, Lead, Tin etc.
Metals can be further divided into two groups-
1. Ferrous Metals – All ferrous metals are having iron as common element. All ferrous
materials are having very high permeability which makes these materials suitable for
construction of core of electrical machines. Examples: Cast Iron, Wrought Iron, Steel, Silicon
Steel, High Speed Steel, Spring Steel etc.
2. Non-Ferrous Metals – All non-ferrous metals are having very low permeability.
Example: Silver, Copper, Gold, Aluminum etc.

Non-Metal materials are non-crystalline in nature. These exist in amorphic or mesomorphic
forms. These are available in both solid and gaseous forms at normal temperature. Normally all
non-metals are bad conductor of heat and electricity. Examples: Plastics, Rubber, Leathers,
Asbestos etc. As these non-metals are having very high resistivity which makes them suitable for
insulation purpose in electrical machines.
Difference between Metals and Non Metals
Sl.
No.
Property Metals Non-Metals
1. Structure
All metals are having crystalline
structure
All Non-metals are having amorphic &
mesomorphic structure
2. State
Generally metals are solid at
normal temperature
State varies material to material. Some are
gas state and some are in solid state at
normal temperature.
3.
Valance electrons
and conductivity
Valance electrons are free to move
within metals which makes them
good conductor of heat &
electricity
Valence electrons are tightly bound with
nucleuses which are not free to move. This
makes them bad conductor of heat &
electricity
4. Density High density Low density
5. Strength High strength Low strength
6. Hardness Generally hard Hardness is generally varies
7. Malleability Malleable Non malleable
8. Ductility Ductile Non ductile
9. Brittleness Generally non brittle in nature Brittleness varies material to material
10. Luster Metals possess metallic luster
Generally do not possess metallic luster
(Except graphite & iodine)

Other classification of engineering materials:
Engineering materials can also be classified as below-
1. Metals and Alloys
2. Ceramic Materials
3. Organic Materials
Metals are polycrystalline bodies which are have number of differentially oriented fine crystals.
Normally major metals are in solid states at normal temperature. However, some metals such as
mercury are also in liquid state at normal temperature. Pure metals are having very a low
mechanical strength, which sometimes does not match with the mechanical strength required for
certain applications. To overcome this draw back alloys are used.
Alloys are the composition of two or more metals or metal and non-metals together. Alloys are
having good mechanical strength, low temperature coefficient of resistance. Example: Steels,
Brass, Bronze, Gunmetal, Invar. Super alloys etc.
Ceramic materials are non-metallic solids. These are made of inorganic compounds such as
Oxides, Nitrides, Silicates and Carbides. Ceramic materials possess exceptional Structural,
Electrical, Magnetic, Chemical and Thermal properties. These ceramic materials are now
extensively used in different engineering fields. Examples: Silica, glass, cement, concrete,
garnet, Mgo, Cds, Zno, SiC etc.
All organic materials are having carbon as a common element. In organic materials carbon is
chemically combined with oxygen, hydrogen and other non-metallic substances. Generally
organic materials are having complex chemical bonding. Example: Plastics, PVC, Synthetic
Rubbers etc.

1.2 Structure of metal-unit cell, BCC, FCC and HCP structures
The smallest repeating array of atoms in a crystal is called a unit cell.
Crystal Structures of Metals
When identical spheres are stacked, each successive layer fits into the small spaces where
different spheres come together. This orderly and regular arrangement of the metal balls
minimizes the empty space between them. Closest packing is the most efficient arrangement of
spheres. Atoms of a metal crystal are arranged in similar patterns, called close-packed
structures. Pure metals adopt one of several related close-packed structures as shown below.
Most pure metals naturally adopt one of these three closest packing arrangements.
On the far left is the body-centered cubic (bcc) structure. In that crystal, metal atoms occupy the
eight corners of a cube along with one atom in the very center. The coordination number of each
atom in the body-centered cubic structure is 8.
B.C.C (Body Centered Cubic)
 1 atom at centre of cube and one atom each at all the corners
 No. of atoms per unit cell = Nc/8+Nf/2+Ni/2 Where Nc = No. of atoms at centre, Nf =
No. of atoms at face and Ni = No. of atoms inside.
 Atomic radius = 1.73*a/4, Where a = distance between two adjacent atoms
 Atomic packing radius = 0.68
 v, Mo, Ta, W are having BCC structure at room temperature
 coordination no is 8
 The nearest distance between two atoms = 1.73*a/2

In the face-centered cubic (fcc) structure, there are eight atoms at each corner of the cube and six
atoms in the center of each face. The coordination number of each atom in the face-centered
cubic structure is 12.
F.C.C (Face Centered Cubic)
 1 atom at each corner of cube
 1 atom at the intersection of the diagonal of each of six faces of the cube
 No. of atoms per unit cell = Nc/8 + Nf/2 + Ni/2 = Four atoms
 Atomic radius = 1.41*a/4
 Atomic packing factor = 0.74
 e.g. Cu, Al, Pb, Ni, Co etc
 Coordination number = 12
 Nearest distance between two atoms = a/1.41
 No. of atoms per unit cell shows the density pack
 So, FCC is more density packed than BCC
The hexagonal close-packed (hcp) structure also has a coordination number of 12, but crystals of
this type are hexagonally shaped rather than cubic.
H.C.P. (Hexagonal Close Pack)
 1 atom at each corner of hexagon
 1 atom at each centre of hexagon faces
 1 atom at the centre connecting perpendicular s in three rhombuses
 No. of atoms per unit cell = 6
 Atomic radius = a/2
 Atomic packing factor = 0.74
 Coordination number = 12
 e.g. Zn, Cd, Mg

1.3 Types of microscopes
The table below describes the main types of microscopes within the optical, electron, and
scanning probe categories.
a) Optical microscope
Type Description
Binocular
stereoscopic
microscope
A microscope that allows easy observation of 3D objects at low magnification.
Bright field
microscope
A typical microscope that uses transmitted light to observe targets at high magnification.
Polarizing
microscope
A microscope that uses different light transmission characteristics of materials, such as
crystalline structures, to produce an image.
Phase contrast
microscope
A microscope that visualizes minute surface irregularities by using light interference. It is
commonly used to observe living cells without staining them.
What is a phase contrast microscope?
Differential
interference
contrast
microscope
This microscope, similar to the phase contrast, is used to observe minute surface irregularities
but at a higher resolution. However, the use of polarized light limits the variety of observable
specimen containers.
Fluorescence
microscope
A biological microscope that observes fluorescence emitted by samples by using special light
sources such as mercury lamps. When combined with additional equipment, bright field
microscopes can also perform fluorescence imaging.
Total internal
reflection
fluorescence
microscope
A fluorescence microscope that uses an evanescent wave to only illuminate near the surface of a
specimen. The region that is viewed is generally very thin compared to conventional
microscopes. Observation is possible in molecular units due to reduced background light.
Laser microscope
(Laser scanning co
focal microscope)
This microscope uses laser beams for clear observation of thick samples with different focal
distances.

Type Description
Multi-photon
excitation
microscope
The use of multiple excitation lasers reduces damage to cells and allows high-resolution
observation of deep areas. This type of microscope is used to observe nerve cells and blood flow
in the brain.
Structured
illumination
microscope
A high-resolution microscope with advanced technology to overcome limited resolution found in
optical microscopes that are caused by the diffraction of light.
b) Electron microscope
Type Description
Transmission electron microscope (TEM), scanning
electron microscope (SEM), etc.
These microscopes emit electron beams, not light
beams, toward targets to magnify them.
c) Scanning probe microscope (SPM)
Type Description
Atomic force microscope (AFM), scanning near-
field optical microscope (SNOM), etc.
This microscope scans the surface of samples with a
probe and this interaction is used to measure fine
surface shapes or properties.
d) Classification by application
Biological microscope With a magnification ranging from 50x to 1,500x, this microscope uses
sliced samples that are fixed onto slides for observation.
(Binocular) stereoscopic
microscope
The binocular system allows 3D observation of samples, such as insects
or minerals, in their natural state without the need to be sliced. The
magnification ranges from 10x to 50x.
e) Classification by structure
Upright microscope Observes targets from above. This type of microscope is used to observe
specimens on slides.
Inverted microscope Observes targets from below. This microscope is used to observe, for
example, cells soaked with culture in a dish.

1.4 Specimen preparation procedure
Preparation of metallographic specimens generally requires five major operations:
1. Sectioning
2. Mounting (which is optional)
3. Grinding
4. Polishing
5. Etching
Advantages of well-prepared metallographic specimen are:
a) Represent sample.
b) Sectioned ground and polished so as to minimize disturbed surface metal caused by
mechanical deformation.
c) Free from polishing scratches and pits and liquid staining.
d) Polished so that inclusions are preserved intact.
e) It allows the true microstructure to be revealed by etching.
f) Flat enough to permit examination at high magnification.
SECTIONING
While preparing specimen we should ensure that we do not alter the microstructure or damage
fracture features when cutting a specimen. Low-speed cut-off wheels are utilized in cases where
the heat created by standard abrasive cutters must be avoided or to avoid cold working a
material. We ensure ample coolant (when allowable) and proper speed controls during sectioning
operations.
MOUNTING
Mounting samples in plastic provides convenience in handling and protection to the edges of the
specimen being prepared during polishing operations. Specimens are generally mounted in epoxy
in 1 to 1.5 inch diameter molds of a hard polymer. Compression molding materials are typically
either thermosetting (Bakelite) or thermoplastic.

The mounting operation accomplishes three important functions
1) It protects the specimen edge and maintains the integrity of a materials surface features
2) Fills voids in porous materials and
3) Improves handling of irregular shaped samples, especially for automated specimen
preparation.
4) Without damage to the specimen
GRINDING AND POLISHING
Grinding is a most important operation in specimen preparation. The purpose of grinding is to
lessen the depth of deformed metal to the point where the last vestiges of damage can be
removed by series of polishing steps. During grinding the operator has the opportunity of
minimizing mechanical surface damage that must be removed by subsequent polishing
operations. Even if sectioning is done in a careless manner, resulting is severe surface damage;
the damage can be eliminated by prolonged grinding. Grinding is accomplished by abrading the
specimen surface through a sequence of operations using progressively finer abrasive grit. Grit
sizes from 40 mesh through 150 mesh are usually regarded as coarse abrasives and grit sizes
from 180 mesh through 600 mesh as fine abrasives.
Specimens should be cleaned after each grinding steps to avoid any carryover of abrasive
particles to the next step. The grinding abrasives commonly used in the preparation of specimens
are silicon carbide (SiC), aluminium oxide (Al2O3), emery (Al2O3 - Fe3O4), diamond particles,
etc.
ETCHING
Microscopic examination of a properly polished, un-etched specimen will reveal only a few
structural features such as inclusions and cracks or other physical imperfections. Etching is used
to highlight, and sometimes identify, micro structural features or phases present. Even in a
carefully prepared sample, a surface layer of disturbed metal, resulting from the final polishing
stage, is always present and must be removed. The purpose of etching is to optically enhance
micro structural features such as grain size and phase features. Etching selectively alters these
micro structural features based on composition, stress, or crystal structure. The most common
technique for etching is selective chemical etching and numerous formulations

Etchants are usually dilute acid or dilute alkalis in water, alcohol or some other solvent. Etching
occurs when the acid or base is placed on the specimen surface because of the difference in rate
of attack of the various phases present and their orientation. The etching process is usually
accomplished by merely applying the appropriate solution to the specimen surface for several
seconds to several minutes. Nital, a Nitric Acid - Alcohol mixture, is the etchant commonly
utilized with common irons and steels.
Advantages of Etching
• Fast
• Can be reproducible
• No mechanical deformation
• Can be automated
• Can produce excellent surfaces for examination
Disadvantages of Etching
• Conductive specimens only
• Not all alloys can be polished
• Preferential attack or pitting can occur
• No edge retention
• Limited polishing area
• Limited scratch/material removal
• Hazardous Electrolytes
• Temperature control vital
• Establishing correct conditions can be difficult
1.5 Properties of Metals-Physical-mechanical-Thermal properties
Properties of Metals:
The properties of the metal are defined as the special qualities or characteristics of metals that
determine their suitability for a specific engineering application.
Although metals have a wide range of properties, the knowledge of the important properties will
be helpful in the section of the metals for a specific application.

Few of the properties of the metals which are very important are:
1. Mechanical properties of metals
2. Electrical properties
3. Thermal properties
4. Magnetic properties
5. Chemical properties
1) Mechanical properties:
Mechanical properties of metal indicate the nature of its inherent behavior under the action of the
external force. Or, Mechanical properties are the properties of the metal which are associated
with its ability to resist failure under the action of external forces. Some of the most important
Mechanical properties of the metal are:
a. Elasticity:
This property of the metals by virtue of which they are able to regain the original shape and size
after the removal of the load is called elasticity. It is a very important property, since all cutting
tools and metallic objects to maintain their original shape while working and after the removal of
the applied force.
b. Plasticity:
The plasticity may be defined as the property of metal by virtue of which a permanent
deformation takes place without fracture whenever it is subjected to the action of external
forces. Most of the metals have been found to possess good plasticity. This property is very
important in forming shaping an extruding operation. Some metals are shaped in cold
conditions, for example, deep drawing of sheets.
c. Ductility:
The ductility may be defined as the property of metals by virtue of which they can be drawn into
wires or elongated before rupture takes place. This property depends largely upon tenacity and to

some extent on hardness. Ductility of metal is higher when cold than hot, hence wires are drawn
in cold condition. The following common metals have ductility in decreasing order: Gold,
Platinum, silver, iron, copper, aluminum, nickel, zinc, tin, and lead.
d. Brittleness:
The brittleness may be defined as the property of metal by virtue of which it will fracture
suddenly without any appreciable deformation. Metals that are less ductile will be brittle. Cast
iron is one of the best examples of brittle metals.
e. Hardness:
The hardness may be defined as the property of metal by virtue of which resist, abrasion,
indentation, and scratch by relatively harder materials. It is expressed related to the hardness of
some standard minerals. Diamond, quartz, corundum, etc. are the harder minerals.
f. Toughness:
Toughness may be defined as the property of the metal by virtue of which we can observe
maximum energy before fracture takes place. It is measured by the amount of energy that is a
unit volume of material has after being stressed up to the point of fracture. Toughness decreases
with an increase in temperature. It is a very important property that is considered while selecting
the material for power press, punch, pneumatic, hammer, etc.
g. Stiffness:
Stiffness is also known as the rigidity of metal. It may be defined as the property by virtue of
which the metal will not deform or deflect when the load is applied.
h. Resilience:
Resilience may be defined as the property of metal by virtue of which it stores energy and resists
shock and impact loads. It is measured by the amount of energy that can be stored per unit
volume after stressed up to the elastic limit. The material of higher resistance is used for spring.

i. Creep:
The creep may be defined as the property of metal by virtue of which it deforms continuously
and slowly under a steady load. Metal generally exhibit creep at Higher temperatures. The creep
is considered an important property while designing the part of the IC Engines and turbine
blades as they are subjected to high pressure at high temperatures.
2) Electrical properties:
The characteristic of a metal which enables the flow of electric current through it is called
electrical properties. The most important electrical properties of metals are Conductivity,
Resistivity, and Dielectric Strength.
a. Conductivity:
The conductivity may be defined as the electrical property of the metal by virtue of which allows
the flow of electric current. It is also defined as the reciprocal of resistance. The metals such as
copper and Aluminium are good electrical conductors. Since they are also highly ductile, they
are used for making electrical transmission wires. Pure metals have good conductivity at room
temperature. The material which is bad conductors is called insulators.
b. Resistivity:
The resistivity may be defined as Electrical property of the metal by virtue of which it impedes
or resists the flow of electric current. It is also defined as the reciprocal of conductivity. It
increases linearly with an increase in temperature.
c. Dielectric Strength:
The insulating material will have the insulating ability up to a certain range of voltage. If the
operating voltage is increased gradually, at some voltage it loses its insulating property. The
minimum voltage that can be applied to the insulating material which results in the destruction of
the insulating properties of the material is defined as the dielectric strength. It is used in the
selection of insulating materials.

3) Thermal Properties:
The thermal properties of the metals are the characteristics of the metal which are influenced by
the application of heat. For example, when metals are heated, they observe the heat energy
resulting in the change of dimension, the flow of heat from higher temperature region to load
temperature region, liquefaction of metals from the solid-state when temperatures are raised
beyond the melting point, electrical conductivity, etc.
a. Thermal Conductivity:
Thermal conductivity images the ability of the metal to transmit heat energy through it. The
higher the thermal conductivity, the greater will be the rate at which heat is conducted. Pure
metals show only small changes in thermal conductivity with temperature. The thermal
conductivity of Copper and Aluminium increases as the temperature decreases until a maximum
reached.
b. Thermal Expansion:
All metals and alloys to a greater or lesser extent expand when heated and contract when cooled.
The amount of expansion and contraction will be proportional to the change in temperature. The
thermal expansion is the characteristic of metals and alloys. This property of the metals will be
useful in the application such as shrink-fit and bi-metal alloys.
c. Specific Heat:
The specific heat of a metal may be defined as the quantity of heat required to raise the
temperature of a unit mass of a substance through 1 Degree Celsius.
d. Melting Point:
The melting point is defined as the temperature at which it begins to melt when the heat is added
to it.

4) Magnetic Properties:
Magnetic properties refer to the metal and alloys such as iron, steel and associated alloying
elements such as cobalt and Nickel. All other materials are non-magnetic. Metals and alloys are
classified as either hard or soft. Hard magnetic materials retail magnetism after the initial
magnetism has been removed. Soft magnetic materials can be easily magnetized or
demagnetized.
Magnetic materials are used in a large variety of electrical and electronic components like
computers, televisions, video cassettes, and a transducer, etc.
a. Permeability:
Magnetic permeability is defined as a measure that indicates the ease in which magnetism may
be developed in the materials. Hard magnetic materials have a low permeability Where are soft
magnetic materials have a high permeability.
b. Coercive Force:
The coercive force is defined as the force which opposes the magnetizing force. It is applied to
remove previous magnetization or residual magnetism. The Coercive force must be very small in
magnetic materials.
c. Hysteresis:
When a ferromagnetic material is subjected to a gradually increasing magnetic field,
simultaneously there will be a corresponding increase in the intensity of magnetization. When
the field strength, is decreased to zero. In order to reduce it to zero, a certain amount of magnetic
field is applied in the reverse direction. A similar phenomenon is observed even in the negative
direction.
The change in the intensity of magnetization always lags behind the change in the magnetic field
strength. This phenomenon of magnetic materials called hysteresis.

5) Chemical Properties:
Some of the important chemical properties considered in the selection of materials are corrosion,
composition and acidity and alkalinity.
a. Corrosion:
The surface of the metal starts deteriorating due to the chemical reaction when pure metals are
exposed to the atmosphere of our environment containing liquid and gases. The Surface
deterioration caused by the chemical reaction is called corrosion. The two simple examples of
corrosion are iron rusting and formation of a green film on the surface of copper.
b. Composition:
The properties of metal depending on the chemical composition of the elements present in the
metals and alloys. By varying the proportion of the chemical composition the desired properties
may be imparted.
c. Acidity and Alkalinity:
Acidity is the Acid characteristics of the metals. Alkaline is the characteristic that neutralizes the
acidity. Corrosion of steel is minimized by mentioning the boiler water alkaline.

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