This presentation discusses line defects called dislocations, including edge and screw dislocations. Edge dislocations occur when an extra half plane of atoms is introduced above or below a slip plane, distorting the crystal structure near the dislocation line. Screw dislocations involve a shear displacement of one plane of atoms relative to the next. Burgers circuits and Burgers vectors are also introduced to characterize dislocations. Crystallographic directions refer to vectors between points, while planes refer to layers of atoms.

1. Presentation On
 Line Defects
&
 Planes & Directions

2. Muhammad Umair Bukhari
Engr.umair.bukhari@gmail.com
www.bzuiam.webs.com
03136050151

3. Line Defects
 It is also called as “Dislocations”
 There are two types of Dislocations
 1- Edge Dislocations
 2- Screw Dislocations

4. Edge Dislocation
 Figure shows a simple cubic crystal
subjected to shearing stress on its upper
and lower half
 SP indicate the slip plane

5.  Upper part of the crystal above the slip
plane moves left w.r.t the below part
 This shearing will leave an extra vertical
half plane “cd” below the slip plane and an
extra half plane “ab” above the slip plane

7.  Due to the extra half plane “ab” the
crystal is distorted
 This distortion decreases as we move
away from the edge of this half plane
because at large distances from this lower
edge of extra half plane atom tends to be
arranged as they would have been in a
perfect crystal

8. Boundry of this additional plane is known as
“ Edge Dislocation”.

9. Screw Dislocation
 Screw Dislocation is shown in figure
 The upper front portion in the following
figure has been sheared by one atomic
distance to the right relative to the lower
front portion

11. Screw Dislocation

12.  Term Screw for such defect is derived
from the fact that lattice planes of the
crystal spiral the dislocation line .

13. Burger’s Circuit &
Burger’s vector
Burger’s circuit is any atom to atom path
taken in a crystal containing dislocations
which forms a closed loop.
In defect free crystal the burger’s circuit
will not close.
The vector required to complete the circuit
is called burger’s vector.

14. In Edge Dislocation

15. In Screw Dislocation

16. Crystallographic Direction & Planes
Line between two points or a vector is called
“Crystallographic Direction”
The layers of atoms along which atoms are
arranged are known as
“Crystallographic planes”