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EA222 > Exam 2: Chapters 5 & 6 > Flashcards

Exam 2: Chapters 5 & 6 Flashcards

1
Q

On a stress strain graph, where is the plastic region?

A

along the straight line

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2
Q

True or false?
Diffusion along grain boundaries is generally faster than through the crystal lattice regardless of which diffusion mechanism is considered.

A

True

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3
Q

Al and Ni are both FCC. The melting temperature of Al is 419 degrees C while the melting temperature of Ni is 1453 degrees C. At 400 degrees C, which one would you expect to have the faster self diffusion rate?

A

Aluminum

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4
Q

How would you expect the diffusion coefficient, D, to change for the following changes in a diffusion situation?

  1. Temp increase
  2. diffusing species (solute) changed to one that is smaller
  3. material being diffused through (solvent) changes from FCC to HCP
A
  1. D increases
  2. D increases
  3. no change in D
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5
Q

Hot work

A

Permanent deformation of metals and alloys above the temperature at which a strain-free microstructure is produced continuously (recrystallization temperature).

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6
Q

Cold Work

A

strain-hardening

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7
Q

Annealing

A

A heat treatment used on a metal to soften it.

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8
Q

Extrusion

A

A plastic-forming process in which a material under high pressure is reduced in cross section by forcing it through an opening in a die.

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9
Q

Forging

A

A primary-processing method for working metals into useful shapes in which the metal is hammered or pressed into shape.

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10
Q

Wire drawing

A

A process in which wire stock is drawn through one or more tapered dies to the desired cross section.

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11
Q

True or false

Hardness decreases with the amount of cold work performed?

A

False

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12
Q

True or false
The diffusion coefficient, D, generally gets smaller in value as the size of the diffusing species (solute) is made smaller.

A

False

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13
Q

Hardness

A

A measure of the resistance of a material to permanent deformation.

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14
Q

Slip

A

The process of atoms moving over each other during the permanent deformation of a metal.

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15
Q

Slip system

A

A combination of a slip plane and a slip direction.

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16
Q

Deformation twinning

A

A plastic deformation process in which a large group of atoms is displaced to form a region of a metal crystal lattice that is a mirror image of a similar region.

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17
Q

True or false

Carburizing a metal’s surface makes it harder , stronger, and more ductile?

A

False

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18
Q

What is a consequence of cold working?

A

decrease in ductility
elongated grains
increases in strength and hardness

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19
Q

True or false

Carbon diffuses faster through FCC iron than it does through BCC iron

A

False

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20
Q

List some strengthening methods

A
  1. reducing grain size
  2. cold work
  3. solid solution strengthening
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21
Q

What is a consequence of recrystallization?

A

equiaxed grains
decrease in hardness
decrease in stregth

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22
Q

True or false

Diffusion is generally faster when it is substitutional type versus interstitial type.

A

False

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23
Q

True or false
For a ductile material, the engineering stress-engineering strain curve for a tensile test reaches a maximum when the specimen begins to neck. This peak value is the ultimate tensile strength.

A

True

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24
Q

True or false

A casting is generally not worked after it is solidified

A

true

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25
Why do strengthening mechanisms increase yield stress?
Strengthening mechanisms modify the crystalline structure of the material in such a way that it takes more applied stress to get them to move
26
True or false | The diffusion coefficient, D, increases in value as the temperature is raised.
True
27
On a stress strain curve, what axis is the stress? what is the symbol
y axis | sigma
28
True or false Carbon is a smaller atom than iron. Therefore, iron generally diffuses faster through itself than carbon does through iron.
False
29
True or false | Hot work is accomplished by working the metal while recrystallization is occurring at the same time.
true
30
On a stress strain curve, where does the fracture occur?
on the very end of the line/curve
31
True or false | Diffusion in solids is much faster than in liquids
false
32
Elastic deformation
When a metal deformed by a force returns to its original dimensions after the force is removed.
33
Engineering stress
Average uniaxial force divided by original cross-sectional area.
34
Engineering strain
Change in length of sample divided by the original length of sample.
35
Shear stress
Shear force, S, divided by the area, A, over which the shear force acts.
36
Modulus of elasticity
Stress divided by strain in the elastic region of an engineering stress-strain diagram for a metal.
37
Yield strength
In the U.S., this is determined for 0.2% strain.
38
Ultimate tensile strength
The maximum stress in the engineering stress-strain diagram.
39
On a stress strain curve, where is the yield strength?
on the stress axis, the highest point of plastic deformation (the highest point in the straight line)
40
On a stress strain curve, where is the value of percent elongation divided by 100?
on the strain axis, where the highest point of the curve is
41
True or false | In order to recrystallize a material, you must bring the temperature very close to the melting temperature.
false
42
Annealing
A heat treatment process applied to a cold-worked metal in order to soften it.
43
Recovery
The first stage in the annealing process that results in removal of residual stresses.
44
Recrystallization
The second stage of the annealing process in which new grains start to grow and dislocation density decreases significantly.
45
Grain growth
The third stage of the annealing process in which new grains start to grow in an equiaxed manner.
46
Superplasticity
The ability of some metals to deform plastically by 1000% to 2000% at high temperatures and low loading rates.
47
Nanocrystalline metals
Metals with grain size smaller than 100 nm.
48
Hall-Petch relationship
An empirical equation that relates the strength of a metal to its grain size.
49
Strain hardening
The hardening of a metal or alloy by cold working.
50
Solid solution strengthening
Strengthening a metal by alloying additions.
51
The three types of annealing starting from lowest temperature to highest are?
recovery, recrystallization, grain growth
52
On a stress strain curve, where is the ultimate tensile strength?
on the strain axis, the highest y coordinate of the curve, where derivative = 0
53
Assuming the same temperature and same concentration of vacancies for both cases, which would you expect to have faster diffusion: Ag in a single crystal of Ag or Ag in a polycrystalline Ag?
Ag in a polycrystalline Ag
54
True or false | A wrought material is one that has been worked in some way.
True
55
Substitutional diffusion
The migration of solute atoms in a solvent lattice in which the solute and solvent atoms are approximately the same size.
56
Self-diffusion
Diffusion in which the solute and the solvent are identical.
57
Interstitial diffusion
The migration of solute atoms in a solvent lattice in which the solute and solvent atoms have a size difference greater than 15%, generally speaking.
58
Steady state conditions
For a diffusing system there is no change in the concentration of the diffusing species with time at different places in the system
59
Diffusivity
A measure of the rate of diffusion in solids at a constant temperature.
60
Fick's first law of diffusion in solids
The flux of a diffusing species is proportional to the concentration gradient at constant temperature.
61
Non steady state condtitions
For a diffusing system the concentration of the diffusing species changes with time at different places in the system.
62
Fick's second law of diffusion in solids
The rate of change of composition is equal to the diffusivity times the rate of change of the concentration gradient at constant temperature.
63
On a stress strain curve, where is the strain? What is the symbol
on the x-axis | epsilon (sort of) (e looking thing)
64
True or false For a substitutional type diffusion, D gets larger as temperature increases because the atoms are vibrating more at higher temperature and the number of vacancies increases at higher temperature.
True

EA222 (10 decks)

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