Question

The primary mechanism for deformation by twinning is

• A. Shear stress rearranges the crystal structure into mirror-image segments
• B. Atoms jump from one lattice position to another
• C. Dislocations move along slip planes
• D. Grain boundaries move through the material

Hint:

Plastic Deformation Mechanisms. Slip: Movement of dislocations on slip systems. Twinning: A portion of the lattice shears into a mirror-image orientation across a twinning plane. Twinning is less common than slip but important in some metals (e.g., HCP) or under specific conditions (low temp, high strain rate).

Answer 1

The Correct Option is A

Plastic deformation in crystalline materials occurs primarily by slip (movement of dislocations along specific planes) and twinning.
- Slip: Involves the movement of dislocations on preferred crystallographic planes (slip planes) and directions, causing blocks of crystal to slide past each other without changing the crystal orientation within the blocks.
(Option 3 describes slip).
- Twinning: Involves a portion of the crystal lattice shearing or displacing uniformly such that the atoms rearrange into an orientation that is a mirror image of the parent lattice across a specific plane (the twinning plane).
This rearrangement occurs in response to shear stress.
(Option 1 describes twinning).
Atom jumping (Option 2) relates to diffusion.
Grain boundary movement (Option 4) relates to grain growth or creep mechanisms.
Twinning is characterized by the formation of these mirror-image regions due to shear stress.