Material and Metallurgy Introduction

Unit 1: Properties, Structure of
Materials and Strengthening
Mechanism Part 1
FACULTY: PROF. Y. M. KHAN
Subject: Materials & Metallurgy
Asst. Professor,
Dept. of Mechanical Engineering, ICEEM, Aurangabad

What is Metallurgy?
It is the branch of science and technology concerned with the production,
purification and properties of metals.

What is a material?
The matter from which a thing is or can be made.

CLASSIFICATION OF MATERIALS
Metals Ceramics

Properties of Materials
Strength
It is the property of a material which opposes the deformation or
breakdown of material in presence of external forces or load.
Materials which we finalize for our engineering products, must have
suitable mechanical strength to be capable to work under different
mechanical forces or loads.

Toughness
It is the ability of a material to absorb the energy and gets plastically
deformed without fracturing. Its numerical value is determined by the
amount of energy per unit volume. Its unit is Joule/ m3.
Value of toughness of a material can be determined by stress-strain
characteristics of a material. For good toughness, materials should have
good strength as well as ductility.
For example: brittle materials, having good strength but limited ductility are
not tough enough. Conversely, materials having good ductility but low
strength are also not tough enough. Therefore, to be tough, a material
should be capable to withstand both high stress and strain.

Hardness
It is the ability of a material to resist to permanent shape change due to
external stress. There are various measure of hardness – Scratch
Hardness, Indentation Hardness and Rebound Hardness
Brittleness
Brittleness of a material indicates that how easily it gets fractured when it
is subjected to a force or load. When a brittle material is subjected to a
stress it observes very less energy and gets fractures without significant
strain. Brittleness is converse to ductility of material. Brittleness of
material is temperature dependent. Some metals which are ductile at
normal temperature become brittle at low temperature.

Malleability
Malleability is a property of solid materials which indicates that how easily
a material gets deformed under compressive stress. Malleability is often
categorized by the ability of material to be formed in the form of a thin
sheet by hammering or rolling. This mechanical property is an aspect of
plasticity of material. Malleability of material is temperature dependent.
With rise in temperature, the malleability of material increases.
Ductility
Ductility is a property of a solid material which indicates that how easily a
material gets deformed under tensile stress. Ductility is often categorized
by the ability of material to get stretched into a wire by pulling or drawing.
This mechanical property is also an aspect of plasticity of material and is
temperature dependent. With rise in temperature, the ductility of material
increases.

Creep
Creep is the property of a material which indicates the tendency of material to
move slowly and deform permanently under the influence of external
mechanical stress. It results due to long time exposure to large external
mechanical stress with in limit of yielding. Creep is more severe in material that
are subjected to heat for long time.
Fatigue
Fatigue is the weakening of material caused by the repeated loading of the
material. When a material is subjected to cyclic loading, and loading greater
than certain threshold value but much below the strength of material (ultimate
tensile strength limit or yield stress limit), microscopic cracks begin to form at
grain boundaries and interfaces. Eventually the crack reaches to a critical size.
This crack propagates suddenly and the structure gets fractured. The shape of
structure affects the fatigue very much. Square holes and sharp corners lead to
elevated stresses where the fatigue crack initiates.

Mechanism Part 2
Asst. Professor,

Structure of metals
Crystal Structure: A regular repetitious pattern in which atoms of a crystalline
material arrange themselves is know as crystal structure
Or
Crystal structure is a description of the ordered arrangement of atoms, ions or
molecules in a crystalline material.

Unit Cell
The block formed by arrangement of small group of atom is called as Unit Cell.
Or
It is the smallest repeating unit/pattern which lattice is built is called unit cell

Space Lattice
The regular arrangement of an infinite set of points(atom, ions, molecules) in a
three dimensional space is called as space lattice.

Types of Crystal Structure (metals)
1. Simple Cubic Structure (SC)
Corner
Atom
Rare due to poor packing (only Po has this structure)

2. Body Centered Cubic Structure (BCC)
Corner
Atom
Examples of bcc include iron, chromium, tungsten, and niobium
Centre
Atom

3. Face Centered Cubic Structure (FCC)
Corner
Atom
Examples of fcc include aluminium, copper, gold and silver.
Face
Atom

4. Hexagonal Closed Packed Structure (HCP)

• 3D Projection
• 2D Projection
A sites
B sites
A sites
examples include beryllium, cadmium, magnesium, titanium, zinc and zirconium

Atomic Radius(r)
Atomic Radius is defined as half the distance between nearest neighbors in a
crystal of an element. It is possible to calculate the atomic radius by assuming
the atoms are sphere in a crystal structure & the lattice parameters are known.
Average number of atoms in Unit Cell(Nav)(N)
After knowing the arrangement of the atoms inside the unit cell, the number of
atoms per unit cell can be calculated by using formula
Nav =
𝑁𝑐
8
+
𝑁𝑓
2
+
𝑁𝑖
1
Nc- Total No. of Corner atoms
Nf- Total No. of Face atoms
Ni- Total No. of interior/center atoms

Atomic Packing Factor(APF)
In crystallography, atomic packing factor (APF), packing efficiency or density
of packing or packing fraction is the fraction of volume that is occupied by
constituent particles(atom/ion/molecules) in a unit cell. It is a dimensionless
quantity and always less than unity. In atomic systems, by convention, the
APF is determined by assuming that atoms are rigid spheres.
APF =
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑎𝑡𝑜𝑚𝑠 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑐𝑒𝑙𝑙
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑢𝑛𝑖𝑡 𝑐𝑒𝑙𝑙
=
𝐴𝑣𝑔.𝑛𝑜.𝑎𝑡𝑜𝑚𝑠 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑐𝑒𝑙𝑙 ∗𝑣𝑜𝑙.𝑜𝑓 𝑎𝑡𝑜𝑚

AR, APF for various structures
Corner
Atom
1. Atomic Radius(r)= a/2
2 . Nav=
𝑁𝑐
8
+
𝑁𝑓
2
+
𝑁𝑖
1
=
8
8
+
0
2
+
0
1
= 1
3. APF =
=
=
1 ∗ 4
3π𝑟3
𝑎3 =
π
6
=0.52
Interatomic
Distance 1. Simple Cubic Structure (SC)
Ref: All figures are adapted from book of William D Callister

Corner
Atom
1. Atomic Radius(r)= 𝟑𝒂/𝟒
2. Body Centered Cubic Structure (BCC)
Centre
Atom
A
B C
D
E
F G
H
A
E G
C
r
2r
A
E
G F
E
G
4r
a
a
𝟐𝒂
a
1 2
From fig 1= AG= r+2r+r= 4r - 1
From fig 2= EG2 = a2 +a2 - 2
From fig 1= AG2= EG2 + AE2 = 3a2 - 3
From eqt 1, 2, 3 = AG2= (4r)2 = 3a2
Radius(r)= 𝟑𝒂/𝟒

2 . Nav=
𝑁𝑐
8
+
𝑁𝑓
2
+
𝑁𝑖
1
=
8
8
+
0
2
+
1
1
= 1+1= 2
3. APF =
=
=
1 ∗ 4
3π𝑟3
𝑎3 =
0.68

Corner
Atom
1. Atomic Radius(r)= 𝟐𝒂/𝟒
2 . Nav=
𝑁𝑐
8
+
𝑁𝑓
2
+
𝑁𝑖
1
=
8
8
+
6
2
+
0
1
= 4
3. APF =
=
=
1 ∗ 4
3π𝑟3
𝑎3 =
0.74
3. Face Centered Cubic Structure (FCC)
Face
Atom

1. Atomic Radius(r)=𝒂/𝟐
2 . Nav=
𝑁𝑐
6
+
𝑁𝑓
2
+
𝑁𝑖
1
Modified Formula
=
12
6
+
2
2
+
3
1
= 6
3. APF =
=
= 0.74
4. Hexagonal Closed Pack(HCP)

Coordination Number
It is defined as the number of nearest(equidistant) atoms which are directly
surrounding a given atom. When its large the structure is said to be closely
packed.
1. Simple Cubic Structure (SC)= Coordination No= 6
SC 6
BCC 8
FCC 12
HCP 12
Coordination Number

Atoms in a crystallographic planes
The layers of atoms or the planes along which the atoms are arranged are
known as atomic or crystallographic planes or index of plane

Miller Indices
The orientation of plane in a lattice is indicated by the index of
plane.
Miller Indices are reciprocals of the fractional intercepts which the
plane makes with crystallographic axes.
The miller system for designating the crystallographic planes and
directions is universally accepted.
The procedure to find Miller Indices is as follows

Y
X
Z
r
q
p
c
a
b
1. Find out the intercept made by the plane on three
reference axes.
E.g. assume that these intercepts are p, q, r
Procedure to Find Miller Indices
2. Convert these intercepts to fractional
intercepts by dividing with their axial lengths, if
the axial lengths are a, b, c
then the fractional intercepts will be
𝑝
𝑎
,
𝑞
𝑏
,
𝑟
𝑐
3. Find out reciprocals of these fractional
intercepts
𝑎
𝑝
,
𝑏
𝑞
,
𝑐
𝑟
4. Convert these reciprocals to the whole number by common multiplication with a LCM.
Let us call these numbers as h, k, l.
Incidentally for a cubic system axial length is a=b=c so they become
1
𝑝
,
1
𝑞
,
1
𝑟

5. Enclose these numbers in bracket (parenthesis) as (h k l).
These notations represents Miller Indices.
Y
X
Z
r
q
p
c
a
b
(h k l)
Note: If the plane passes through origin then shift the
origin to new position for finding index of plane.

Y
X
Z
1
1. The intercepts- ꚙ, 1, ꚙ
2. Fractional intercepts- ꚙ /1, 1/1, ꚙ /1
3. Reciprocal of fractional intercepts- 1/ ꚙ, 1/1, 1/ ꚙ
4. Convert to whole number – 0, 1, 0
5. Put in bracket- (0 1 0)
1. Find out the intercepts
2. Convert the intercepts to fractional intercepts
3. Reciprocal these fractional intercepts
4. Convert to whole number
5. Put in bracket
(0 1 0)

Y
X
Z
1
2/3
1/3
1. Find out the intercepts
2. Convert the intercepts to fractional intercepts
3. Reciprocal these fractional intercepts
4. Convert to whole number
5. Put in bracket
1. The intercepts- 1/3, 2/3, 1
2. Fractional intercepts-
1/3
1
,
2/3
1
,
1
1
3. Reciprocal of fractional intercepts- 3/1, 3/2, 1/1
4. Convert to whole number – 6, 3, 2

Y
X
Z
Y
X
Z
-1
1
1. The intercepts- 1, -1, ꚙ
2. Fractional intercepts-
1
1
,
−1
1
,
ꚙ
1
3. Reciprocal of fractional intercepts- 1, -1, 0
4. Convert to whole number – 1, -1, 0

Solidification: Definition of terms
1. System: Part of the universe under study is called ‘system’.
2. Phase: Phase is homogenous physically distinct and mechanically separable
part of the system under study.
3. Variable: A particular phase exist under various conditions of temperature,
pressure and concentration these parameters are called as ‘variables of the
phase’.
4. Components: The elements present in the system are called as components.
For example Cu-Al system contains ‘copper and aluminum’ as components.
5. Alloy: Alloy is a ‘mixture of two or more elements’ having metallic property.
The elements present in larger proportion is a metal and other can be metal
or nonmetal. The element with larger amount is called as ‘base metal’ or
‘parent metal’ or ‘solvent’ and the other elements are called ‘alloying
elements’ or ‘solute ‘.

1. Solid solution: It is an alloy in which atoms of solute are distributed in the
solvent and has the same structure as that of solvent. Solid solutions have
different compositions with similar structures and are liquid solutions such as
sugar in water.
2. Substitutional & Interstitial Solid Solution
Substitutional solid solution: this solid solution means the atoms of B
element i. e. solute are substituted at the atomic site of A i. e. solvent.

Random/Disordered & Regular/Ordered Substitutional Solid Solution
In regular solid solution the substitution of B atoms in A element is
by definite order while there is no definite order or regularity in
random solid solution.
Regular Random

Interstitial Solid Solution
In Interstitial solid solutions the atoms of B (solute) occupy the
interstitial site of A(solvent) atoms. This type of solid solution
formation is favored when atomic size of B is very much small as
compared to A

Intermediate phase
In any alloy there is addition of alloying element into base metal.
During addition, of elements of solute form bond with solvent.
There is specific limit for any alloying system to add alloying element
into the parent metal to get the properties of resultant alloy.This
specific limit is called as ‘solid solubility’
Beyond solid solubility limit it is also possible to add alloying element
into parent metal when but when solubility limit exceeds a second
phase starts to appear with solid solution this second phase is called
as ‘intermediate phase’.

Solidification of a pure metal
The first step in the solidification is the formation of nuclei the nucleus can be regarded as a small cluster of atoms having a
right crystalline arrangement. When the melt is cooled below its melting point nuclei begin to form in many part of the melt at
same time.
The rate of nuclei formation depends on the rate of ‘undercooling or supercoiling’ and also on pressure and impurities
which facilitates the nucleation.
At any temperature below melting point , a nucleus has to be of certain minimum size so that it will grow this size is called as
‘critical size’ of nucleus.
Particles smaller that critical size will get dissolved by vigorous bombardment of neighboring atoms these are called
‘embryos’. With the temperature lowered the vibrations of atoms gradually decreases thus increasing chance of survival of
embryos.
Liquid
Metal
Solid
Temp
Time
Freezing
Point

Therefore, with decrease in temperature the critical size also
decreases which means with at lower temperature the nuclei with
smaller size can also survive.
Hence, at lower temperatures nuclei become progressively smaller in
size but the number greatly increases.
Growth of nuclei occur by diffusion process which is a function of
temperature hence, nucleation and rate of growth is also function of
temperature.

Mechanism Part 8
Asst. Professor,

Cooling curves for binary eutectic alloy
Binary Eutectic is a homogenous mixture of two solids which forms
at a constant temperature during cooling & melts during heating at
a constant temperature.
Binary Eutectic Transformation
Constant Temp

Temp
0C
Time
A
B C
D
L
L+S1+S2
S1+S2
Cooling curves for binary eutectic alloy

Temp
0C
Time
A
B C
D
L
L+S1+S2
S1+S2
Applying Gibb’s Phase Rule
In Region AB
P+F=C+1
P = 1, C = 2
F = 2
Bi-variant
In Region BC
P+F=C+1
P = 3, C = 2
F = 0
Invariant
In Region CD
P+F=C+1
P = 2, C = 2
F = 1
Univariant
F = 2
F = 0
F = 1

Eutectic transformation occurs at definite composition
called eutectic composition. If this definite composition of
off(differ) from its fixed value then such an alloy is called
either HYPO or HYPER Eutectic Alloy
Cooling curves for off eutectic alloy(binary)

Cooling curves for off eutectic alloy(binary)
Temp
0C
Time
A
B
C D
L
L+S1 (Or S2 ) L+S1+S2
E
S1+S2

Temp
0C
Time
A
B
C D
L
L+S1 (Or S2 )
L+S1+S2
E
S1+S2
Applying Gibb’s Phase Rule In Region AB
P+F=C+1
P = 1, C = 2
F = 2
Bi-variant
In Region BC
P+F=C+1
P = 2, C = 2
F = 1
Univariant
In Region CD
P+F=C+1
P = 3, C = 2
F = 0
Invariant
In Region DE
P+F=C+1
P = 2, C = 2
F = 1
Univariant
F = 2
F = 1
F = 0
F = 1
The start of the solidification is called liquidus
because above this temp metal is in liquid
state, and end of solidification is called solidus
because below it metal is in solid state.

Polymorphism
Many Substances exist in more than one stable crystalline form. The various
forms have the same composition but different crystal structure. Such a change
in crystal structure with same composition is called ‘Polymorphism’. This may be
due to change in the pressure or temperature or both.
It is observed in pure metals and compounds as well, both organic and
inorganic.
The Polymorphism of metals is often called ‘Allotropy’ and the transformation
is reversible with change in temperature at a given pressure.
The metals which exhibit polymorphism, their different crystal forms are called
‘Polymorphs’.
The substance which exhibit polymorphism is described either Dimorphic or
Trimorphic depending on its number of forms.

Iron Allotropy, Cooling Curve for Pure Iron
Temp 0C
Time
A
Liquid
B C
D E
F G
H I
J
δ iron
γ iron
α iron (Non Magnetic)
α iron (Magnetic)
1539
1400
910
768

Defects in Crystal
Types of Crystal Defect
1. Point defect
2. Line defect
3. Planer Defect
4. Volume Defect

Edge and Screw Dislocation
Line defects

Material and Metallurgy Introduction

Material and Metallurgy Introduction

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