The document discusses various topics related to engineering materials including their classification, structure, microstructure, sample preparation techniques, and properties. It defines materials and material science. Materials are classified as metals and alloys, non-metals, and composite materials. Metals have crystalline structures such as body centered cubic, face centered cubic, and hexagonal close packed. Microstructure is studied using various types of microscopes. Sample preparation involves cutting, mounting, polishing, and etching specimens. Key properties of metals discussed are physical, mechanical, thermal, electrical, magnetic, and chemical.

1. Unit-I
BASICS OF ENGINEERING MATERIALS

2. Topics
• 1.1 Classification of Engineering Materials
• 1.2 Structure of metal-unit cell, BCC, FCC and HCP structures
• 1.3 Microstructure-type of microscopes
• 1.4 Sample preparation-etching process-types of etchant
• 1.5 Properties of metals-Physical-mechanical- Thermal properties

3. • Material: It is defined as the substance (most often solid)
that is meant used for certain applications.
• Material Science: It is the scientific discipline which
establishes the relation between the structure, properties
of the materials and the processing done on them.

4. 1)Metals & Alloys
a)Ferrous Metals
b) Non-Ferrous Metals
2)Non-Metals
a)Ceramics
b) Plastics
3)Composite materials
a) Steel-reinforced concrete
b) Vinyl-coated steel

6. Metals : It is defined as material which is solid at room temperature , has relatively
high density, high melting temperature and good electrical and thermal conductivity.
Ex : Iron, Steel, Aluminium, Copper, Lead, Zinc, Tin, etc.
Classification of metals:
a) Ferrous Metals b) Non Ferrous Metals
a) Ferrous Metals:- Ferrous is derived from Latin word ferrum means iron. The
metals which contain iron as a base are called ferrous metals.
Ex: Pig iron, Cast iron, Wrought iron, Steel.
b)Non Ferrous metals: Nonferrous metals are those which do not contain iron as
base. Ex: Aluminium, Copper , Lead ,Tin ,Zinc ,Magnesium ,Nickel.
Metals

7. Non- Metals
Ceramics: Ceramics are those which are inorganic, nonmetallic materials.
Ex: Silicon carbide ,Aluminium oxide ,Clay etc
Plastics: It may be defined as organic material that can be easily moulded or shaped
mechanically or chemically to give solid structure at ordinary temperature. These are
classified it to two types.
1) Thermo Plastics – PVC, Nylon, Polystyrene.
2) Thermosetting Plastics – Polyesters, Epoxy Resins.
Composite Materials: Composite materials are the combination of two or more
organic or in-organic components.
Ex: Steel-reinforced concrete, Vinyl-coated steel

8. Atom: The smallest particle of an element that can exist is called atom.

9. 1.2. Crystalline solid
A crystalline solid or a crystal is
defined as a solid in which the atoms are
arranged in a very regular and orderly
fashion in a three dimensional pattern
called space lattices. Most of the solids
(including all metals) are crystalline in
structure and are made up of aggregate of
single crystals. In a crystalline solid each
atom is located at a definite point in space
at a definite distance from and in a definite
angular orientation to other atoms
surrounding it.

10. Crystallography: It is the science of studying the geometric from and other physical
properties of crystalline solids by using X-rays, electron beams etc.

11. Space lattice
A crystal is formed when the atoms arrange themselves in an orderly three
dimensional pattern called space lattice. Thus space lattice is the three
dimensional array of points (atoms) in which every point has surroundings identical
with that every other point. These points with identical surroundings are called
lattice points.

12. Unit cell
A unit cell is the smallest geometrical pattern repeating in a space lattice. It’s over and over repetition
builds up the whole crystal. It is formed by drawing a network of straight lines through selected lattice
points. Each unit cell in a space lattice is identical in size, shape and orientation with every other unit cell.
Figure shows a unit cell of a three-dimensional crystal lattice. It is formed by intercepts a, band c along
the three axes respectively. The three angles (α, β and γ) are called interfacial angles. Both the intercepts
and interfacial angles constitute the lattice parameters of the unit cell. The values of intercepts and
interfacial angles are known, then it possible to determine the form and actual size of the unit cell.

13. Metal structure
In crystalline/metal structure, the atoms are located at regular recurring positions in three
dimensions. The pattern may be replicate millions of times within a given crystal. The structure
can be viewed the form of a unit cell, which is the basic geometric grouping of atoms that is
repeated. There are several types of pattern in which metallic atoms can arrange themselves on
solidification, but the common three are as follows:
1. Body-Centered-Cubic (BCC) structure
2. Face-Centered-Cubic (FCC) structure
3. Hexagonal-Closed-Packed (HCP) structure
Arrangement/number of atoms in crystals: The atoms that belong to the unit cell are called the
basic atoms, its number is different from one shape of arrangement to another, and this number
can be found from the following equation:
N = NC + NI + NF
Where, N: is the number of the basic atoms in the unit cell.
NC: is the number of the atoms in the corner.
NI: is the number of the atoms inside the cube.
NF: is the number of the atoms in the center of the face.

14. 1.Body-Centered-Cubic (BCC) structure
In this structure the unit cell contains eight atoms at each corner and
one atom at centre. Out of eight corner atoms each atom is shared by
a cube.
Total number of atoms in B.C.C = (1/8)×8+1=2
Examples: Chromium,
Potassium, Molybdenum,
Barium, Tungsten, and
Iron.

15. 2. Face-Centered-Cubic (FCC) structure
In this structure the unit cell contains eight atoms at each corner and six atoms
in centre of each faces. Eight corner atoms are shared by eight surrounding
cubes and six faces centered atoms are shared by two adjacent cubes.
Total number of atoms in F.C.C= (1/8)×8+(1/2)×6
=1+3=4
Examples: Aluminum,
Copper, Lead, Nickel, Iron,
Gold, Silver.

16. 3. Hexagonal-Closed-Packed (HCP) structure
In this type of structure, the unit cell contains one atom at each corner of the
hexagonal prism, one atom each at the centre of the hexagonal faces and
three more atoms within the body of the cell.
Total number of atoms in H.C.P= 3 + (1/2)×2 + (1/6)×6×2 = 6
Examples: Beryllium,
Cadmium, Magnesium,
Zinc.

17. 1.3. Microstructure
Preparing a metal/alloy specimen and viewing its microstructure under the metallurgical
microscope greatly helps in the identification of metal alloy.
Microscopes: The closest distance of separation (i.e. resolution) visible to the human naked
eyes is 0.1 mm. Inside details of solids, crystals, unit cells, atoms, electrons, and imperfection
demand for visibility of much smaller dimensions. The smaller dimensions may be as small as
1 Angstrom (10-10 m) or less. These situations need a magnified vision. This is possible
through a microscope. Microscopes of various magnification ratios are used according to the
need. Their magnification generally varies between 5 to 1000000. Microscopes are broadly
classified into following main categories.
1. Optical microscope
2. Electron microscope
3. Field ion microscope
4. Scanning tunneling microscope

18. Types of microscopes with magnification and applications
Type Range of magnification Used in study of
Optical microscope 10 to 2000 times linear Microstructure
Electron microstructure 100000 times linear
Finer particles,
dislocations
Field ion microscope Up to 1000000 times Imperfections
Scanning tunneling
microscope
more than 1000000 times
Atomic image
microscope

19. Optical microscope

20. Optical microscope
The microscopic examination is based on optical principle. In it the rays from light
source is passed on to a glass reflector through a diffusing disc and an Iris
diaphragm as shown in the figure. The diffusing disc helps in diffusing the light,
the Iris diaphragm controls the width of light beam, and the reflector kept at 45o
partially reflects the light rays on to the sample (or object).After illuminating the
polished sample; the rays return by reflection, pass through the objective and
glass reflector, and then form an image. This image can be seen through eye-
piece to get the view of sample surface.
The eye piece is carried by a ‘draw tube’ at its top end. The draw tube can slide
within the ‘body tube’ of microscope through a rack and pinion mechanism, on
rotating the coarse and fine adjustment knobs. By doing so the distance between
objective and the eye-piece can be varied for focusing the object. The coarse
adjustment is done for initial focusing and the fine adjustment for final focusing.

21. 2. Electron microscope
In this operation, the tungsten filament T is thermionically heated. Due
to this the electrons are emitted which are collimated by metallic grid M.
The collimated electron beam is accelerated by anode A to a potential
about 5000 volts. Accelerated beam is then focused on the object by
the magnetic condenser coil. The object is placed on a cellulose film
held in a holder. The incident electron beam on the object scans it, and
then the objective coil produces a magnified image I1 of the object.
This image I1 acts as an object for projector coil which magnifies it to
image I2. Final image I2 may be seen on a fluorescent screen or on a
photographic plate. Whole system is placed in a metal casing which is
evacuated to produce vacuum. Arrangements of keeping and moving
the object and its adjustment are incorporated in the microscope.

22. 2. Electron microscope
Electron microscope may be used
in the fields of medicine and
biology to study bacteria and virus,
in colloidal solutions to examine
minute particles, in textile industry
to study structure of fibres, and
industries like paper, paints,
plastics, lubricants and metals.

23. 1.4. Specimen preparation
The procedure for preparing the specimen for micro examination involves the following steps:
i) Selection of specimen: The specimen should be so selected that it represents the whole section
or the entire piece. The specimen is usually very small in size.
ii) Cutting of specimen: Alter selecting a particular area in the whole mass, the specimen may be
removed with the help of a saw, a trepanning tool, an abrasive wheel, etc.
iii) Mounting the specimen: In case, the specimen is too small to be held in hand it should be
mounted in thermoplastic resin or some other low melting point alloy.
iv) Obtaining flat specimen surface: Primary requirement is to first obtain a reasonably flat surface
this can be achieved by using a fairly coarse file or machining or grinding by using a motor driven
emery belt.
v) Grinding (Intermediate and fine): It is carried out by using emery paper of progressively finer
grades. The emery papers used should be of very good quality.

24. vi) Rough polishing: A little quantity of diamond powder is used for polishing action.
vii) Fine polishing: The polishing compound alumina (Al2O3) used is fine polishing.
Which removes fine scratches and very thin distorted layer remained in the rough polishing
stage.
viii) Etching: After fine polishing the metal specimens are usually etched to make the
grain boundaries visible. Etching imparts unlike appearances to the metal constituents and
thus makes metal structure apparent under the microscope.
The polished specimen, before etching is thoroughly washed in running water and etching is
done either by (a) Immersing the polished surface of the specimen in the Etching reagent or
by (b) rubbing the polished surface gently with a cotton swab wetted with Etching agent.
ix) Specimen inspection: After the etching the specimen is again washed thoroughly and
dried. Now the specimen is read for study under the microscope.

25. Common Etching agents
Sl.No. Metal/alloy Etching agents
1 Wrought iron 5 percent solution of nitric acid in alcohol
2 Normalized carbon steels, Annealed carbon
steels, Cast iron
2 percent solution of nitric acid in alcohol
3 Hardened and tempered high carbon steels 1 percent solution of nitric acid in alcohol
4 Low alloy steels 2 percent solution of nitric acid in alcohol
5 Silicon for the electrical industry 10 percent solution of nitric acid in alcohol
6 Austenitic steels 5 percent solution of hydrochloric acid in alcohol
7 Stainless steels 10 percent solution of hydrochloric acid in alcohol
8 High speed steels 10 gm of potassium ferri-cyanide and 10 gm of
potassium hydroxide in 100 c.c. of water
9 Copper alloys 10 percent solution of ammonium per-sulphide in
water
10 Aluminium alloys Solution of 2 percent hydrofluoric acid and 20
percent nitric acid in water
11 Magnesium alloys 2 to 4 percent solution of nitric acid in alcohol.

26. 1.5. Properties of metals
The following properties of metals:
A. Physical properties
B. Mechanical properties
C. Thermal properties
D. Electrical properties
E. Magnetic properties
F. Chemical properties

27. A. Physical properties
It is any property that is measurable, whose value describes a state of
a physical system. Some important physical properties are:
1. Luster
2. Colour
3. Density
4. Boiling Point
5. Melting/Freezing Point

28. 1. Luster: The ability of the surface of a material to reflect light is known as luster.
2. Colour: The property of material of displaying a particular hue in the normal
day –night is known as colour.
3. Density: The mass per unit volume of a material is known as density.
4. Boiling Point: The temperature at which a liquid material changes to vapour
(gas) at atmospheric pressure is known as boiling point.
5. Melting/Freezing Point: The temperature at which a solid material changes to
liquid at atmospheric pressure is known as melting point.

29. B. Mechanical Properties
These are the properties which deal with the behavior or characteristics
of material when it is subjected to external force, load & torque. Some important
mechanical properties are:
1. Strength
2. Elasticity
3. Plasticity
4. Ductility
5. Malleability
6. Brittleness
7. Hardness
8. Toughness
9. Stiffness
10. Resilience
11. Creep
12. Fatigue
13. Impact Strength

30. B. Mechanical Properties
1. Strength: It may be defined as it is the capacity of material to
withstand destruction (damage) under the action of external load.
2. Elasticity: It is the Property of material by virtue of which ,it is eligible
to regain its original shape after removal of applied force or Load.
Ex: Rubber , Steel etc.
3. Plasticity: It is the Property of material by virtue of which ,it is not
eligible to regain its original shape after removal of applied force or
Load. Ex: Steel at red hot condition, Clay etc.

31. B. Mechanical Properties
4. Ductility : It is the Property of material by virtue of which ,it can be drawn in to
thin wires or elongated before rupture takes place .
Ex: copper , aluminum , gold etc.
5. Malleability : It is the Property of material by virtue of which , it can be drawn in
to thin sheets or it can be hammered and rolled in to thin sheets.
Ex: Copper , Tin, lead aluminum etc .
6. Brittleness : It may be defined as the property of material by virtue of which it will
fracture(Break) suddenly without any deformation (change in shape & size).it is
opposite to ductility
Ex: Pig iron, Cast iron , Glass etc.

32. B. Mechanical Properties
7. Hardness : It may be defined as the property of material by virtue of which it will
resists Abrasion , Indentation and Scratching. It is very important property while
selecting materials for cutting tools and metallic components which have to resist
wear while working.
Ex: Diamond, Quartz etc.
8. Toughness : It may be defined as the property of material by virtue of which it
can absorb max energy before fracture takes place.
OR
It is the property of the material to resist fracture due to high impact loads
like hammer blows. This property is desirable in parts subjected to shock and
impact loads. It is a very important property while selecting the material for power
press, punch, pneumatic hammer etc.
Ex: Mild steel , wrought iron etc.

33. B. Mechanical Properties
9. Stiffness : It may be defined as the property of material by virtue of which the
metal will not deform or deflect when the load is applied. It is also known as rigidity
of the metal. Although steel is stronger than cast iron, cast iron is preferred for
machine beds and frames because it is more rigid. The Modulus of elasticity is the
measure of stiffness.
10. Resilience : It may be defined as the property of material by virtue of which it
will withstand sudden shocks and impact loads. This property is essential for
spring materials.

34. B. Mechanical Properties
11. Creep : When the part is subjected to a constant stress at high temperature for
a long period of time, it will undergo a slow and permanent deformation called
creep. This property is considered in designing internal combustion engine, Boilers
and turbines.
12. Fatigue : The failure of a material, under repeatedly applied stress is called
fatigue. some machine parts such as axles, crank shafts, connecting rods ,springs,
and pinion are subjected to fatigue
13. Impact Strength: It is the capacity of a material to resist shock or sudden
application of load.

35. C. Thermal properties
These are the properties that are exhibited by a material
when the heat is passed through them. Some important
thermal properties are:
1. Specific heat (Heat capacity)
2. Thermal Expansion
3. Thermal conductivity
4. Thermal stress

36. C. Thermal properties
1. Specific heat (Heat capacity): The heat capacity of a material can be defined
as the amount of heat required to change the temperature of the material by one
degree.
2. Thermal Expansion: When heat is passed through a material, its shape
changes. Generally, a material expands when heated. This property of a material
is called thermal expansion. There can be a change in the area, volume, and
shape of the material.
3. Thermal conductivity: It is the property of a material to conduct heat through
itself.
4. Thermal stress: The stress experienced by a body due to either thermal
expansion or contraction is called thermal stress.