Presentation On Line Defects & Planes & Directions
Muhammad Umair Bukhari Engr.email@example.com www.bzuiam.webs.com 03136050151
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
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 & PlanesLine between two points or a vector is called “Crystallographic Direction”The layers of atoms along which atoms are arranged are known as “Crystallographic planes”