Question

How does dislocation movement by cross-slip differ from climb?

• A. Cross-slip involves movement along a different slip plane, while climb involves vertical movement out of the slip plane.
• B. Cross-slip requires higher temperatures than climb.
• C. Climb is faster than cross-slip.
• D. Climb involves multiple dislocations, cross-slip only one.

Hint:

Dislocation Movement. Slip: Conservative movement on slip plane. Cross-Slip: Screw dislocation changes slip plane (conservative). Climb: Edge dislocation moves perpendicular to slip plane via vacancy/interstitial diffusion (non-conservative, high temperature).

Answer 1

The Correct Option is A

Both cross-slip and climb are mechanisms by which dislocations can overcome obstacles, but they differ significantly: - Cross-slip: This is a mechanism specific to screw dislocations.
A screw dislocation moves primarily on its slip plane, but if blocked, it can change to a different, intersecting slip plane that also contains its Burgers vector direction, allowing it to bypass the obstacle.
It's a conservative process (doesn't require atom diffusion).
- Climb: This mechanism applies primarily to edge dislocations (or edge components of mixed dislocations).
It involves the dislocation moving *perpendicular* to its slip plane (vertical movement out of the plane).
This movement requires the addition or removal of atoms from the dislocation's extra half-plane, which occurs via the diffusion of vacancies or interstitial atoms.
Climb is a non-conservative process and is typically significant only at higher temperatures where diffusion is appreciable.
Option (1) accurately contrasts the movement along a new slip plane (cross-slip) with movement out of the slip plane (climb).
Cross-slip generally occurs more readily at lower temperatures than climb (making Option 2 incorrect).
Climb is diffusion-controlled and usually slower than slip/cross-slip (making Option 3 incorrect).
Both can involve individual dislocations (Option 4 incorrect).