basic concept of dislocation
TRANSCRIPT
DISLOCATIONMONIKA.M
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Today's Overview
5 Reference
4 Charactrestics
3 Type of dislocation
2 Cause of dislocation
1 Introduction
One step to the next
Dislocations are happened because of stress applied.
1There can be millions of dislocations in each cubic millimeter of a metal
2The presence of dislocations strongly influences many of the properties of materials
3
TEM image of dislocated crystal
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
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
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
PARTIAL DISLOCATION
MIXED DISLOCATION
EDGE DISLOCATION
SCREW DISLOCATION
DISLOCATIONS ARE CLASSIFIED INTO FOUR
Where mixed and partial dislocations are not so important as screw and edge dislocation.
CHARACTRESTICS
1When 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.
4Same sign on same plane repulse each other whereas opposite signs attract and annihilate on meeting.
Thank you
Monika.M
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