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.

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