Question

Cross slip is observing

• A. screw dislocation
• B. edge dislocation
• C. twinning
• D. bending

Hint:

Remember:
Screw dislocation $\rightarrow \mathbf{b} \parallel \mathbf{t}$ $\rightarrow$ Can cross slip.
Edge dislocation $\rightarrow \mathbf{b} \perp \mathbf{t}$ $\rightarrow$ Cannot cross slip (can only climb via thermal diffusion).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks which type of crystal defect or dislocation is capable of undergoing the deformation process known as "cross slip".

Step 2: Key Formula or Approach:
Cross slip is a mechanism of plastic deformation where a dislocation moves from one slip plane to another intersecting slip plane.
For this movement to occur, the Burgers vector of the dislocation must lie along the intersection line of the two planes.

Step 3: Detailed Explanation:

• Screw Dislocation: In a screw dislocation, the dislocation line is parallel to its Burgers vector ($\mathbf{b} \parallel \mathbf{t}$). Because of this parallel orientation, the dislocation line and its Burgers vector do not define a unique slip plane. It can slip on any plane containing the dislocation line. When it encounters an obstacle, it can easily shift (cross slip) onto an intersecting slip plane.

• Edge Dislocation: In an edge dislocation, the dislocation line is perpendicular to its Burgers vector ($\mathbf{b} \perp \mathbf{t}$). This perpendicular arrangement defines a single, unique slip plane. The edge dislocation is restricted to this plane and cannot change planes unless it undergoes climb, which requires diffusion.

• Twinning and Bending: These are macroscopic modes of deformation and are not dislocation defects that undergo cross slip.

Step 4: Final Answer:
Cross slip is observed in screw dislocations.