Dislocations and Strengthening Mechanisms - Chapter 9

Question 1

Two fundamental dislocation types?

Answer 1

Edge and Screw

Question 2

Slip?

Answer 2

The process by which plastic deformation is produced by dislocation motion.

Question 3

Dislocation density?

Answer 3

The number of dislocations.

Total dislocation length per unit volume.

The number of dislocations that intersect a unit area of a random section.

Question 4

Two reasons the grain boundary acts as a barrier to dislocation motion?

Answer 4

1. The two grains are of different orientations, a dislocation passing into a grain must change it’s direction of motion, this becomes more difficult as the orientation increases.
2. The atomic disorder within a grain boundary region results in a discontinuity of slip planes from one grain to another.

Question 5

Hall Petch Equation?

Answer 5

Delta[y] = delta[o] + KyD^-1/2

D = average grain diameter

Other are constants depending on the material

Question 6

Solid Solution Strengthening?

Answer 6

Alloying with impurity atoms that go into either substitutional or interstitial solid solution.

Question 7

Strain Hardening

Answer 7

When a ductile metal becomes harder and stronger as it is plastically deformed.

Question 8

Cold Working

Answer 8

When the temperature at which deformation takes place is cold relative to absolute melting temperature

%CW = (Ao-Ad/Ao) x 100

Question 9

Recovery:

Answer 9

During recovery, some of the stored internal strain energy is relieved by virtue of dislocation motion.

There is some reduction in number of dislocations.

Dislocation configurations are produced having low strain energies.