Question

1. State the difference between: Single crystal and polycrystalline materials Deformability of BCC and FCC metals. Strength and UTS of metals.

Answer 1

1. Difference between single crystal and polycrystalline structure is that in single crystal internal atomic pattern is repeated whereas there is no periodicity across a polycrystalline sample

Polycrystalline material – Aggregate of several crystals or grains

Single crystal – only one grain or crystal and hence, no
grain boundaries.

2.The deformity depends on the fact of slip system.

FCC have less slip system when compared to BCC so FCC offers more deformity.

The deformation of metals involve the motion of large number of defects on certain crystallographic planes. These defects are crystallographic in nature and are commonly called as dislocations.

FCC has 12 number of slip systems per unit cell available for deformation.BCC has 48 number of slip systems.

There are 48 systems in BCC lattice but slip plane of each is different.The slip plane changes but slip direction doesn’t changes and that’s why BCC structure mostly deforms by screw dislocation.But in FCC the slip plane and slip direction changes simultaneously and that’s why it under goes edge dislocation. That makes the slip plane and slip direction as major parameter to differentiate the deformability of different lattice structure.

3.Ultimate tensile strength (UTS) is the maximum stress that a material can withstand while being stretched or pulled. The ultimate tensile strength of a material is calculated by dividing the cross-section area of the material tested by the stress placed on the material, generally expressed in terms of pounds or tons per square inch of material.

strength is defined as the amount of stress where a predetermined amount of plastic (irreversible) deformation occurs. If the applied stress is lower than the strength the deformation is always elastic

strength is always lower than the ultimate tensile strength.