Presentation On

Line Defects

&

Planes & Directions

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Muhammad Umair Bukhari

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

Edge Dislocation

Figure shows a simple cubic crystal subjected to shearing stress on its upper and lower half

SP indicate the slip plane

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

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

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

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

Screw Dislocation

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

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.

In Edge Dislocation

In Screw Dislocation

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”