ANS:C - slip

Slip refers to the mechanism by which atoms in a crystal lattice of a metal rearrange themselves to accommodate plastic deformation. When a metal is subjected to an external force, such as during cold working processes like rolling or forging, the atoms in the crystal lattice are displaced from their equilibrium positions. This displacement causes the atoms to move along specific crystallographic planes, resulting in the deformation of the material without fracture. Key points about slip:

1. Crystal lattice structure: Metals have a crystalline structure composed of closely packed atoms arranged in a regular pattern. Slip occurs along specific planes within this lattice structure.
2. Dislocation movement: Slip occurs due to the movement of linear defects called dislocations within the crystal lattice. Dislocations allow atoms to move past one another with relative ease, facilitating plastic deformation.
3. Activation energy: Slip requires the movement of dislocations, which involves overcoming an activation energy barrier. Under an applied stress, dislocations can overcome this barrier and move, allowing the material to deform plastically.
4. Preferred slip planes: Each metal has specific crystallographic planes along which slip is most likely to occur. These planes have the lowest shear stress required for slip to initiate.
5. Orientation dependence: Slip occurs preferentially in certain crystallographic directions and planes based on the crystal structure of the metal. This orientation dependence influences the mechanical properties of the material.

In summary, slip is a fundamental mechanism of plastic deformation in metals, enabling them to undergo shape changes without fracturing. It plays a crucial role in processes such as cold working, where metals are shaped into desired forms through controlled deformation.