Dislocations are defects in crystal structures caused by stress and strain. There are different types of dislocations including edge dislocations and screw dislocations. Dislocations cause plastic deformation in metals by allowing slip and twinning to occur when stress is applied. Slip involves the sliding of crystal planes over one another, resulting in a permanent displacement, while twinning involves the rearrangement of atoms across a twinning plane. Dislocations are classified into types and influence many material properties, such as making metals able to undergo shaping processes that involve plastic deformation.

1. DISLOCATION
MONIKA.M
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2. Today's Overview
5 Reference
4 Charactrestics
3 Type of dislocation
2 Cause of dislocation
1 Introduction

3. One step to the next
Dislocations are
happened because
of stress applied.
1
There can be millions
of dislocations in each
cubic millimeter of a
metal
2
The presence
of dislocations strongly
influences many of the
properties of materials
3

4. TEM image of dislocated crystal

5. CAUSES OF DISLOCATION
They cause “PLASTIC DEFORMATION”.
i,e..nothing but the material returns to its
original shape and size after the applied
stress (load) is released.
1
The ability of a metal to undergo plastic
deformation is one of the important property
which is utilized for shaping of metals by
various fabrication process such as rolling,
forging, drawing, extrusion etc.,
2

6. SLIP FORMATION
Slip involves sliding of one
plane of atoms over the
other.
1
Slip is a permanent
displacement of one part
of crystal relative to the
other part.
2

7. TWINNING FORMATION
Twinning is a process in
which the atoms in a part
of the crystal subjected to
stress rearrange
themselves
1
The plane across which
the two part are mirror
images is called twinning
plane or composition
plane.
2

8. DISLOCATIONS ARE CLASSIFIED INTO FOUR
Where mixed and partial
dislocations are not so
important as screw and
edge dislocation.

9. CHARACTRESTICS
1
When a metal is plastically deformed,most of energy is
dissipated as heat but app 0.5% is stored internally.
2
Distortions of lattice around dislocation line causes
lattice strains.
3
In screw dislocations-shear strains.This strain field can
affect other dislocations.
4
Same sign on same plane repulse each other whereas
opposite signs attract and annihilate on meeting.

10. Thank you
Monika.M
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