INTRODUCTION TO MATERIALS & METALLURGY.ppt

By
ANSARI ZAKIR SAJID
Asstt. Professor
Department of Mechanical Engg.
School of Engg. And Technology
Anjuman-I-Islam’s
Kalsekar Technical Campus
1
Anjuman-I-Islam's Kalsekar Technical Campus

 Significance of course
 Teaching and examination schemes
 Classification of materials
 Structure of an atom
 Imperfections in crystals
 Deformations
 Strain Hardening
2

 Alloy: Metal having additions of 1 or more metals or non metals
Ceramics: Inorganic crystalline material
Glass: An amorphous material (often but not always) derived
from a molten liquid.
Polymers: Organic materials made by polymerization
Semiconductors: Materials with electrical conductivity between
metallic conductors and ceramic insulators
Composites: Formed from 2 or more materials producing
properties not found in any single material.
3
ACTIVITY

ACTIVITY
Working in groups, make the broad category of materials as
 Metals and Alloys
 Ceramics & Glasses
 Polymers
 Composites
 Semiconductors
Every student has to join one of these groups with a name of the metal,
introduce himself and tell ones properties and applications.
e.g one student would join metals and alloys group and say that i am copper, i
have good electrical conductivity, i am used as wire and in many instruments

 Alloy: Metal having additions of 1 or more metals or non metals
Ceramics: Inorganic crystalline material
Glass: An amorphous material (often but not always) derived
from a molten liquid.
Polymers: Organic materials made by polymerization
Semiconductors: Materials with electrical conductivity between
metallic conductors and ceramic insulators
Composites: Formed from 2 or more materials producing
properties not found in any single material.
6

Significance:
Structure property relationship
Structure at 5 different levels
1.Atomic structure (1 A)
2.Short and Long range atomic Arrangements (10 nm-cm)
3.Nano structure (1-100nm)
4.Micro structure(0.1-100 micro m)
5.Macrostructure(>100 micro m)
7

QUANTUM NUMBERS
1.Principal Quantum number (n)
2.Azimuthal Quantum number (l)
3.Magnetic Quantum number (mi)
4.Spin Quantum number (ms)
n= 1,2,3 …
l= 0,1,2…(n-1)
No. of electrons in a shell = 2n2
Aufbau principal for addition of electrons in orbitals
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Electro negativity: Tendency to gain electrons
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1. Metallic Bond
2. Covalent Bond
3. Ionic Bond
4. Vander wall bonds
14

Lattice:
A lattice is a collection of points, called lattice points, which are
arranged in a periodic pattern so that the surroundings of each
point in the lattice are identical.
Basis:
A group of one or more atoms located in a particular way with
respect to each other and associated with each lattice point is
known as the basis or motif.
crystal structure:
By placing the atoms of the basis on every lattice point we get
crystal structure. (i.e., crystal structure = lattice + basis)
17

Unit cell: The grouping of atoms whose repetition will produce the
crystal is called unit cell.
crystal systems:
Shape and size of unit cell decided by six lattice parameters which
are a, b, c and α, β, γ .
Depending on the relationship of these unit cell is dvided into 7
different groups called crystal systems
1. Cubic, 2. Tetragonal, 3. Orthorhombic,
4. Rhomohedral (also known as trigonal), 5. Hexagonal,
6. Monoclinic, 7. Triclinic.
Bravai’s lattices: The 7 crystal systems are divided into 14 types
depending on basic arrangement of atoms
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Almost all the metals posses one of the following crystal structures
1.Simple cubic (SC)
2.Body centred cubic (BCC)
3.Face centred cubic (FCC)
4.Hexagonal closed packed (HCP)
FEATURES OF A CRYSTAL STRUCTURE
1.Average no of atoms per unit cell
For cubic unit cell For Hexagonal unit cell
Nav=Nc/8+Nf/2+Ni/1 Nav=Nc/6+Nf/2+Ni/1
Where Nav = avg. no of atoms in unit cell
Nc= No. of corner atoms
Nf= No. of atoms in the faces
Ni= No. of interior atoms
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For S.C Nav = 1
For B.C.C Nav = 2
For F.C.C Nav = 4
For H.C.P Nav = 6
2. Atomic radius:
For S.C r = a/2
For B.C.C r = sqrt(3)*a/4
For F.C.C r = sqrt(2)*a/4
For H.C.P r = a/2
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3. Atomic packing factor:
A.P.F=(Volume of atoms per unit cell)/(Total volume of unit cell)
1. For simple cubic
Volume of unit cell = a*a*a
Volume of one atom = (4/3) * π* r*r*r
A.P.F = (4/3) *π* (a/2)*(a/2)*(a/2) / (a*a*a)
= 0.52
2. For B.C.C
A.P.F = 0.68
3. For F.C.C
A.P.F = 0.74
4. For H.C.P.
A.P.F = 0.74
23

4. Coordination Number:
The coordination number is the number of atoms touching a
particular atom, or the number of nearest neighbors for that
particular atom.
For simple cubic
CN = 6
2. For B.C.C
CN = 8
3. For F.C.C
C.N = 12
4. For H.C.P.
C.N. = 12
29

OUTCOME EVALUATION QUESTIONS
1. Classify metals and state properties of each category with
examples and applications.
2. State different types of atomic bondings with differentiating
points.
3. Explain about crystal structure from lattice-basis and unit cell
basis.
4. Explain basic types of crystal structure found in most of the
metals and state the parameters defining their characterstics like
APF etc.
5. Explain method to name crystallographic planes and
crystallographic directions.
36

Imperfections/Defects: Any deviation from an orderly array of
lattice points.
Significance: All the mechanical properties are structure
sensitive properties so depends on defects.
Defects are the areas where deformation starts
Can be categorized as
1.Point defects
2.Line defects
3.Surface defects
Significance of dislocations: Edge dislocation helps in slip and
supports deformation
37

Line defects are either of the two types
1.Edge dislocations
2.Screw Dislocations
Burgers vector:
It is a precise statement of the magnitude and direction of shear
that a dislocation produces.
For edge dislocation – perpendicular to dislocation line
For Screw dislocation – Parallel to dislocation line
43

44
Burger Vector
Direction
of Gliding
Dislocation
Line

48
Gliding
Planes
Direction
of Gliding

Surface defects are either of the two types
1.External Defects
2.Internal Defects
Internal defects can be of
a.Grain boundaries
b.Tilt Boundary
c.Twin Boundary
d.Stacking faults
51

1.External Defects:
It is caused by the atoms present on the surface
Not surrounded by neighboring atoms from the top
They posses higher energy
There might be discontinuities present on the surface
52

a.Grain boundaries:
They separate crystals or grains during crystallization
In a material there may be crystals of various orientations called
grains
Low angle grain boundary – less than 10-15 degr.
High angle grain boundary – more than 10-15 degr.
Possibility of misalignment of atoms of various grains
53

b. Tilt boundary:
Series of aligned dislocations
which helps in motion of
dislocations
Can be regarded as a low
angle grain boundary
55

c. Twin boundary:
A special grain boundary across which there is specific mirror
lattice symmetry
Results from atomic displacement due to application of shear
force
56

British physicist Charles Frank and Thornton Read
Is a mechanism for dislocation multiplication in a slip plane under
shear stress
Consider an edge dislocation AB (A and B being pinned)
Shear stress τ is exerted on the slip plane
A force F = τ *b*x is exerted on AB
Where b=burgers vector and x= length of line AB
This force acts perpendicular to AB to lengthen and curve into an arc
This force is opposed by the line tension of the dislocation of
magnitude Gb2 where G is shear modulus
When it becomes semicircular F= Gb2
This gives τ = Gb/x
If shear stress is more than this value dislocation grows and forms
loops and in this way increases no of dislocations and yield strength
At the end of loop steps equal to 1 burger vector
58

Def. : When load is applied on a material it results in change in
shape and size called deformation
Can be temporary called elastic or permanent called plastic
In elastic material regains original shape and size
In plastic the change is permanent
Characterized by breaking of sufficient no of inter atomic bonds by
movement of dislocations
The force required to break the bonds in a crystal at a single time is
more
Because of dislocation it is carried out at very lower levels of stress
The direction of deformation is called slip direction and the plane of
slip is called the slip plane.
60

A SINGLE CRYSTAL is the one in which there are no grain
boundaries
Atoms are oriented in only one direction
Uniform chemical composition
Produced by controlled solidification of metal
Secondary recrystallization
A POLYCRYSTALLINE material has grain boundaries
62

Deformation in material can take place by
1. Slip
2.Twining
3.Combination of slip and twining
66

Increase in hardness and strength of metal when subjected to plastic
deformation at temp. lower than recrystallisation range.(cold
working)
When metal is plastically deformed, it requires more stress for its
further deformation
Indicated by the given example
76

Strain hardening is due to the increased resistance to dislocations
Some dislocations become struck inside the crystal and oppose the
motion of other dislocations.
STAGES OF WORK HARDENING:
Stage I : Easy glide region
Stage II: Linear hardening region
Stage III: Parabolic hardening region
Stage I: Follows after yield point
Dislocations move over large regions without encountering with
berriers
Stage II: Rapid increase in work hardening rate
As a result several different lattice irregularities are formed
80

Stage III: Region of decreasing rate of strain hardening
At a high value of stress or temp, the dislocations held up in stage II
are able to move in this stage
Also the dislocations which are moved out of the primary slip plane
return back by double cross slip
Thus the rate of work hardening is low
81

Carried out in order to make the metal ductile
Can be done by heat treatment called annealing
Carried out because of 2 processes at elevated temp
Recovery and recrystallisation
These 2 are followed by grain growth
82

Recovery:
During recovery, some of the stored internal strain energy is
relieved by virtue of dislocation motion (in the absence of an
externally applied stress), as a result of enhanced atomic diffusion at
the elevated temperature. There is some reduction in the number of
dislocations, and dislocation configurations are produced having
low strain energies. In addition, physical properties such as electrical
and thermal conductivities and the like are recovered to their
precold-worked states.
Recrystallization:
Recrystallization is the formation of a new set of strain-free and
equiaxed grains.
Recrystallization is a process the extent of which depends on both
time and temperature.
84

Recrystallization:
Recrystallization temp. is the temp at which recrystallization reaches
completion in 1 hour.
Typically it is between ½ to 1/3 of the absolute melting point of the metal.
Depends on amount of prior cold work and purity of alloy
With increase in degree of CW recrystallization temp gets lowered
Recrystallization proceeds more rapidly in pure metals than in alloys.
During recrystallization, grain-boundary motion occurs as the new grain
nuclei form and then grow.
Impurity atoms preferentially segregate at and interact with these
recrystallized grain boundaries so as to diminish their (i.e., grain boundary)
mobilities; this results in a decrease of the recrystallization rate and raises
the recrystallization temperature, sometimes quite substantially
87

Grain growth:
After recrystallization is complete, the strain-free grains will
continue to grow if the metal specimen is left at the elevated
temperature (Figures d–f ); this phenomenon is called grain growth.
Grain growth does not need to be preceded by recovery and
recrystallization; it may occur in all polycrystalline materials, metals
and ceramics alike.
90

END OF MODULE I
OUTCOME OF MODULE I
The learner should be able to
Classify materials,Identify defects in materials and express
the phenomenon of strain hardening of metals.
Is the outcome achieved?
Rate it on a scale of 5
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INTRODUCTION TO MATERIALS & METALLURGY.ppt

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