Chapter 7: Dislocations And Strengthening Mechanisms

Question 1

Plastic deformation as the result of dislocation motion; also, the shear displacement of two adjacent planes of atoms

Answer 1

Slip

Question 2

The total dislocation length per unit volume of material; alternatively, the number of dislocations that intersect a unit area of a random surface section

Answer 2

Dislocation Density

Question 3

The measured strength of a material is ——the theoretical strength.

• greater than
• equal to
• less than

Answer 3

Less than

Question 4

——is the process by which plastic deformation is produced.

-slip
-step
-screw

Answer 4

Slip

Question 5

Dislocation motion is similar to the motion of a ——.

-snake
-caterpillar
-fish

Answer 5

Caterpillar

Question 6

The majority of the deformation energy is——when metals are plastically deformed.

• retained internally
• dissipated as heat
• stored as strain energy

Answer 6

Dissipated as heat

Question 7

The extra half-plane of atoms in an edge dislocation causes a——lattice strain below the half-plane.

-compressive
-tensile
-shear

Answer 7

Tensile

Question 8

The magnitude of the strains around a dislocation line——with radical distance from the dislocation.

• remains constant
• increases
• decreases

Answer 8

Decreases

Question 9

Two edge dislocations of the same sign and lying on the same slip plane will exert——on each other.

• an attractive force
• a repulsive force
• no force

Answer 9

A repulsive force

Question 10

Two edge dislocations of opposite sign and lying on the same slip plane will exert——on each other.

• an attractive force
• a repulsive force
• no force

Answer 10

An attractive force

Question 11

The number of dislocations in a metal——during plastic deformation.

• increases dramatically
• decreases dramatically
• remains constant

Answer 11

Increases dramatically

Question 12

Slightly displacements of atoms relative to their normal lattice positions, normally imposed by crystalline defects such as dislocations, and interstitial and impurity atoms.

Answer 12

Lattice Strain

Question 13

Molybdenum (Mo) has a slip plane——and slip direction——.

• {110}, (111)
• {211}, (111)
• {321}, (111)

Answer 13

{110}, (111)

Question 14

Potassium (K) has——slip systems.

• 6
  -12
  -24

Answer 14

24

Question 15

The Burgers vector for BCC unit cells in terms of the unit cell edge length is——.

• a/2 (110)
• a/2 (111)
• a/3 (1120)

Answer 15

A/2 (111)

Question 16

The combination of a crystallographic plane and, within that plane, a crystallographic direction along which slip (i.e. dislocation motion) occurs.

Answer 16

Slip System

Question 17

A material with——grains is hardest and strongest.

• small
• medium
• large

Answer 17

Small

Question 18

The grain size can be modified by——.

• elastic deformation
• plastic deformation
• plastic deformation with heat treatment

Answer 18

Plastic deformation with heat treatment

Question 19

Grain size reduction improves——.

• strength only
• toughness only
• strength and toughness

Answer 19

Strength and toughness

Question 20

Increasing the concentration of impurity atoms in an alloy will——the alloy’s strength.

• not change
• decrease
• increase

Answer 20

Increase

Question 21

A substitutional atom larger than the host atoms exerts a——strain on the surrounding crystal lattice.

• tensile
• compressive
• shear

Answer 21

Compressive

Question 22

A substitutional atom smaller than the host atoms will tend to move to a position——the slip plane near an edge dislocation.

• below
• above
• on

Answer 22

Above

Question 23

Hardening and strength in of metals that result from alloying in which a solid solution is formed. The presence of impurity atoms restricts dislocation mobility.

Answer 23

Solid-Solution Strengthing

Question 24

Cold working——the yield strength of 1040 steel.

• increases
• decreases
• doesn’t change

Answer 24

Increases

Question 25

Cold working——the tensile strength of brass

• increases
• decreases
• does not change

Answer 25

Increases

Question 26

Cold working——the ductility of copper

• increases
• decreases
• doesn’t change

Answer 26

Decreases

Question 27

The increase in hardness and strength of a ductile metal as it is plastically deformed below its recrystallization temperature.

Answer 27

Strain Hardening

Question 28

The plastic deformation of a metal at a temperature below that at which it recrystallizes

Answer 28

Cold Working

Question 29

——is the relief of some internal strain energy of a previously cold-worked metal.

• grain growth
• recrystallization
• recovery

Answer 29

Recovery

Question 30

Recovery of a cold-worked metal involves dislocation motion due to——.

• external applied stress
• enhanced atomic diffusion
• stored internal strain energy

Answer 30

Enhanced atomic diffusion

Question 31

Physical properties such as electrical and thermal conductivities——during recovery.

• remain unchanged
• return to a pre cold-worked state
• are only slightly affected

Answer 31

Pre cold-worked state

Question 32

The relief of some of the internal strain energy of a previously cold-worked metal, usually by heat treatment.

Answer 32

Recovery

Question 33

The amount of recrystallization depends on——.

-temperature
-time
-both time and temperature

Answer 33

Both time and temperature

Question 34

The recrystallization temperature of a metal alloy is typically——the absolute melting temperature.

-greater than
-equal to
-less than

Answer 34

Less than

Question 35

For metals and metal alloys there is a critical degree of cold work——which recrystallization cannot occur.

-below
-at
-above

Answer 35

Below

Question 36

The formation of a new set of strain-free grains within a previously cold-worked material; normally, an annealing heat treatment is necessary.

Answer 36

Recrystallization

Question 37

for a particular alloy, the minimum temperature at which complete recrystallization occurs within approximately 1 hour

Answer 37

Recrystallization Temperature

Question 38

Grain growth can occur in——.

-metals only
-ceramics only
-both metals and ceramics

Answer 38

Both metals and ceramics

Question 39

During grain growth, ——grains can enlarge.

-small
-large
-all

Answer 39

Large

Question 40

Grain growth——the strength and toughness of a metal.

-increases
-decreases
-doesn’t change

Answer 40

Decreases

Question 41

The increase in average grain size of a polycrystalline material; for most materials, an elevated-temperature heat treatment is necessary

Answer 41

Grain Growth