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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
Q

Why do strengthening mechanisms increase yield stress?

A

Strengthening mechanisms modify the crystalline structure of the material in such a way that it takes more applied stress to get them to move

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26
Q

True or false

The diffusion coefficient, D, increases in value as the temperature is raised.

A

True

27
Q

On a stress strain curve, what axis is the stress? what is the symbol

A

y axis

sigma

28
Q

True or false
Carbon is a smaller atom than iron. Therefore, iron generally diffuses faster through itself than carbon does through iron.

A

False

29
Q

True or false

Hot work is accomplished by working the metal while recrystallization is occurring at the same time.

A

true

30
Q

On a stress strain curve, where does the fracture occur?

A

on the very end of the line/curve

31
Q

True or false

Diffusion in solids is much faster than in liquids

A

false

32
Q

Elastic deformation

A

When a metal deformed by a force returns to its original dimensions after the force is removed.

33
Q

Engineering stress

A

Average uniaxial force divided by original cross-sectional area.

34
Q

Engineering strain

A

Change in length of sample divided by the original length of sample.

35
Q

Shear stress

A

Shear force, S, divided by the area, A, over which the shear force acts.

36
Q

Modulus of elasticity

A

Stress divided by strain in the elastic region of an engineering stress-strain diagram for a metal.

37
Q

Yield strength

A

In the U.S., this is determined for 0.2% strain.

38
Q

Ultimate tensile strength

A

The maximum stress in the engineering stress-strain diagram.

39
Q

On a stress strain curve, where is the yield strength?

A

on the stress axis, the highest point of plastic deformation (the highest point in the straight line)

40
Q

On a stress strain curve, where is the value of percent elongation divided by 100?

A

on the strain axis, where the highest point of the curve is

41
Q

True or false

In order to recrystallize a material, you must bring the temperature very close to the melting temperature.

A

false

42
Q

Annealing

A

A heat treatment process applied to a cold-worked metal in order to soften it.

43
Q

Recovery

A

The first stage in the annealing process that results in removal of residual stresses.

44
Q

Recrystallization

A

The second stage of the annealing process in which new grains start to grow and dislocation density decreases significantly.

45
Q

Grain growth

A

The third stage of the annealing process in which new grains start to grow in an equiaxed manner.

46
Q

Superplasticity

A

The ability of some metals to deform plastically by 1000% to 2000% at high temperatures and low loading rates.

47
Q

Nanocrystalline metals

A

Metals with grain size smaller than 100 nm.

48
Q

Hall-Petch relationship

A

An empirical equation that relates the strength of a metal to its grain size.

49
Q

Strain hardening

A

The hardening of a metal or alloy by cold working.

50
Q

Solid solution strengthening

A

Strengthening a metal by alloying additions.

51
Q

The three types of annealing starting from lowest temperature to highest are?

A

recovery, recrystallization, grain growth

52
Q

On a stress strain curve, where is the ultimate tensile strength?

A

on the strain axis, the highest y coordinate of the curve, where derivative = 0

53
Q

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?

A

Ag in a polycrystalline Ag

54
Q

True or false

A wrought material is one that has been worked in some way.

A

True

55
Q

Substitutional diffusion

A

The migration of solute atoms in a solvent lattice in which the solute and solvent atoms are approximately the same size.

56
Q

Self-diffusion

A

Diffusion in which the solute and the solvent are identical.

57
Q

Interstitial diffusion

A

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
Q

Steady state conditions

A

For a diffusing system there is no change in the concentration of the diffusing species with time at different places in the system

59
Q

Diffusivity

A

A measure of the rate of diffusion in solids at a constant temperature.

60
Q

Fick’s first law of diffusion in solids

A

The flux of a diffusing species is proportional to the concentration gradient at constant temperature.

61
Q

Non steady state condtitions

A

For a diffusing system the concentration of the diffusing species changes with time at different places in the system.

62
Q

Fick’s second law of diffusion in solids

A

The rate of change of composition is equal to the diffusivity times the rate of change of the concentration gradient at constant temperature.

63
Q

On a stress strain curve, where is the strain? What is the symbol

A

on the x-axis

epsilon (sort of) (e looking thing)

64
Q

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.

A

True

EA222 (10 decks)

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