Chapter 7: Dislocations And Strengthening Mechanisms Flashcards
Plastic deformation as the result of dislocation motion; also, the shear displacement of two adjacent planes of atoms
Slip
The total dislocation length per unit volume of material; alternatively, the number of dislocations that intersect a unit area of a random surface section
Dislocation Density
The measured strength of a material is ——the theoretical strength.
- greater than
- equal to
- less than
Less than
——is the process by which plastic deformation is produced.
-slip
-step
-screw
Slip
Dislocation motion is similar to the motion of a ——.
-snake
-caterpillar
-fish
Caterpillar
The majority of the deformation energy is——when metals are plastically deformed.
- retained internally
- dissipated as heat
- stored as strain energy
Dissipated as heat
The extra half-plane of atoms in an edge dislocation causes a——lattice strain below the half-plane.
-compressive
-tensile
-shear
Tensile
The magnitude of the strains around a dislocation line——with radical distance from the dislocation.
- remains constant
- increases
- decreases
Decreases
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
A repulsive force
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
An attractive force
The number of dislocations in a metal——during plastic deformation.
- increases dramatically
- decreases dramatically
- remains constant
Increases dramatically
Slightly displacements of atoms relative to their normal lattice positions, normally imposed by crystalline defects such as dislocations, and interstitial and impurity atoms.
Lattice Strain
Molybdenum (Mo) has a slip plane——and slip direction——.
- {110}, (111)
- {211}, (111)
- {321}, (111)
{110}, (111)
Potassium (K) has——slip systems.
- 6
-12
-24
24
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)
A/2 (111)
The combination of a crystallographic plane and, within that plane, a crystallographic direction along which slip (i.e. dislocation motion) occurs.
Slip System
A material with——grains is hardest and strongest.
- small
- medium
- large
Small
The grain size can be modified by——.
- elastic deformation
- plastic deformation
- plastic deformation with heat treatment
Plastic deformation with heat treatment
Grain size reduction improves——.
- strength only
- toughness only
- strength and toughness
Strength and toughness
Increasing the concentration of impurity atoms in an alloy will——the alloy’s strength.
- not change
- decrease
- increase
Increase
A substitutional atom larger than the host atoms exerts a——strain on the surrounding crystal lattice.
- tensile
- compressive
- shear
Compressive
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
Above
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.
Solid-Solution Strengthing
Cold working——the yield strength of 1040 steel.
- increases
- decreases
- doesn’t change
Increases
Cold working——the tensile strength of brass
- increases
- decreases
- does not change
Increases
Cold working——the ductility of copper
- increases
- decreases
- doesn’t change
Decreases
The increase in hardness and strength of a ductile metal as it is plastically deformed below its recrystallization temperature.
Strain Hardening
The plastic deformation of a metal at a temperature below that at which it recrystallizes
Cold Working
——is the relief of some internal strain energy of a previously cold-worked metal.
- grain growth
- recrystallization
- recovery
Recovery
Recovery of a cold-worked metal involves dislocation motion due to——.
- external applied stress
- enhanced atomic diffusion
- stored internal strain energy
Enhanced atomic diffusion
Physical properties such as electrical and thermal conductivities——during recovery.
- remain unchanged
- return to a pre cold-worked state
- are only slightly affected
Pre cold-worked state
The relief of some of the internal strain energy of a previously cold-worked metal, usually by heat treatment.
Recovery
The amount of recrystallization depends on——.
-temperature
-time
-both time and temperature
Both time and temperature
The recrystallization temperature of a metal alloy is typically——the absolute melting temperature.
-greater than
-equal to
-less than
Less than
For metals and metal alloys there is a critical degree of cold work——which recrystallization cannot occur.
-below
-at
-above
Below
The formation of a new set of strain-free grains within a previously cold-worked material; normally, an annealing heat treatment is necessary.
Recrystallization
for a particular alloy, the minimum temperature at which complete recrystallization occurs within approximately 1 hour
Recrystallization Temperature
Grain growth can occur in——.
-metals only
-ceramics only
-both metals and ceramics
Both metals and ceramics
During grain growth, ——grains can enlarge.
-small
-large
-all
Large
Grain growth——the strength and toughness of a metal.
-increases
-decreases
-doesn’t change
Decreases
The increase in average grain size of a polycrystalline material; for most materials, an elevated-temperature heat treatment is necessary
Grain Growth
