Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Material Science > MAE 3324 Ch4 > Flashcards

MAE 3324 Ch4 Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

Define “crystalline defect.”

A

Refers to a lattice irregularity having one or more of its dimensions on the order of an atomic diameter. Classification of crystalline imperfections is frequently made according to the geometry of the defect.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a point defect?

A

A defect associated with one or two atomic positions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Is a linear defect a one or two-dimensional defect?

A

One dimensional

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the simplest point defect? Describe it.

A

Vacancy

A vacant lattice site. It’s normally occupied but in this case, an atom is missing.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

T or F

All crystalline solids contain vacancies and it is impossible to create materials without them to some extent?

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Vacancies are due to what thermodynamic principle?

A

Entropy. Vacancies increase the entropy of the crystal.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

The number of vacancies in a crystal increases or decreases with what? Give the equation proving this.

A 
Temperature
Nv = number of vacancies
N = total number of atomic sites [#/m^3]
Qv = Energy required to for the formation of a vacancy [J/mol or eV/atom)
T = absolute temp [K]
k = boltsman constant [1.38E-23 J/atom*k

N_v = Nexp(-Qv/(kt))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The number of vacancies increases _______ with temperature?

A

Exponentially.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Define self-interstitial

A

An atom from the crystal that is crowded into an interstitial site which is a small void space that, under ordinary circumstances, is not occupied.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is more likely; self-interstitial or vacancy

A

vacancy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Define “solid solution.”

A

A new metal that is formed by adding impurity atoms to a metal.

Extra Notes: The addition of impurity atoms to a metal results in the formation a solid solution and/or a new second phase depending on the kinds of impurity their concentrations and the temperature of the alloy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Define “solvent” wr/ to solid solutions.

A

The solvent is the element or compound that is present in the greatest amount.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Define “solute” wr/ to solid solutions.

A

The solute is the element or compound in a minor concentration.

“As far as white people go at UTA, you’re the solute.”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What impurity defects are found in solid solutions?

A

Substitutional and interstitial.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

A solid solution is formed when?

A

solute atoms are added to the host material, and the crystalline structure is maintained and no new structures are formed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe a solid solution substitutional impurity.

A

Solute or impurity atoms replace or substitute for the host atoms, creating a new material.

Extra Notes: Several features of the solute and solvent atoms determine the degree to which the former dissolves in the latter. These are expressed as the four Hume-Rothery rules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe the first Hume-Rothery rule.

A

Atomic size factor: Appreciable quantities of a solute may be accommodated in this type of solid solution only when the difference in atomic radii between the two atom types is less than about +/- 15%. Otherwise, the solute atoms create substantial lattice distortions and new phase forms.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe the second Hume-Rothery rule

A

Crystal Structure: For appreciable solid solubility, the crystal structures for metals of both atoms types must be the same.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Describe the third Hume-Rothery rule

A

Electronegativity factor: The more electropositive one element and the more electronegative the other, the greater the likelihood that they will form an intermetallic compound instead of a substitutional solid solution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Describe the fourth Hume-Rothery rule

A

Valances: Other factors being equal, a metal has more of a tendency to dissolve another metal of higher valency than to dissolve one of a lower valency.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

For both FCC and BCC crystal structure, there are how many types of interstitial sites?

A

2.
Tetrahedral
octahedral
These are distinguished by the number of nearest neighbor host atoms (coordination number).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Tetrahedral interstitial sites have a coordination number of?

A

Four

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Octahedral interstitial sites have a coordination number of?

A

Six

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

T or F

In metallic materials, the relatively high atomic packing factor means that interstitial positions are relatively large?

A

False

Interstitial positions are very small in metals.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are the two most common ways to express the composition of alloys?

A

Weight percent and atom percent.

26
Q

What is the formula for the weight percent for a two element alloy?

A

For two atoms c1 an c2, the concentration of c1 is
C1 = m1/(m1+m2)*100
mi = weight of individual element.

27
Q

Atom percent is based upon?

A

moles of one element vs total moles in the alloy.

28
Q

The number of moles in some specified mass of a hypothetical element 1 may be computed as?

A

n_m1 = m1’/A1
where
m1’ = mass in grams
A1 = atomic weight

29
Q

Computation of atom percent in a two-element alloy.

A

C1’ = n_m1 / (n_m1 + n_m2) * 100

30
Q

Define a “dislocation.”

A

A linear or one-dimensional defect around which some of the atoms are misaligned.

31
Q

What is an edge dislocation?

A

When an additional plane of atoms terminates inside a crystal. See figure 4.4 in the book.

32
Q

What is a screw dislocation and how is it formed?

A

A dislocation that is due to shear stress. Induces a twisting or helical structure. See figure 4.5 in the book.

33
Q

What is the burgers vector?

A

The magnitude and direction of the lattice distortion associated with a dislocation.

34
Q

For and edge dislocation, the Burgers vector, and the dislocation line are?

A

perpendicular.

35
Q

For a screw dislocation, the Burgers vector and the dislocation line are

A

parallel

36
Q

How might dislocations be introduced into a material?

A
  1. Solidification
  2. Plastic deformation
  3. quenching
37
Q

Define “interfacial defects.”

A

Boundaries that have two dimensions and normally separate regions of the material that have different crystal structures and/or crystallographic orientations.

38
Q

What do interfacial defects include?

A
  1. External surfaces
  2. Grain boundaries
  3. Phase boundaries
  4. Twin boundaries
  5. Stacking faults

“Every Goat Poops Twice on Saturday.”

39
Q

Describe “external surfaces” wr/ to interfacial defects.

A

At the boundary of the material, surface atoms are not bonded to the max number of nearest neighbors and are therefore in a higher energy state than the atoms inside the material. The bond of these surface atoms that are not satisfied gives rise to a surface energy expressed in units of energy per unit area. To reduce this energy, materials tend to minimize if at all possible the total surface area.

40
Q

Describe “grain boundaries” wr/ to interfacial defects.

A

The boundary separating two small grains or crystals having different crystallographic orientations in a polycrystalline structure.

41
Q

Describe “phase boundaries” wr/ to interfacial defects.

A

Exist in multi-phase materials in which a different phase exists on each side of the boundary. Has a large role in mechanical characteristics.

42
Q

Describe “twin boundaries” wr/ to interfacial defects.

A

A special type of grain boundary in which there is a specific mirror lattice symmetry; that is, atoms on one side of the boundary are located in mirror image positions to those of the atoms on the other side.

Twins result from atomic displacement due to shear forces (mechanical twins) or from annealing heat treatments.

43
Q

T or F

Atoms are always vibrating in their lattice though this doesn’t mean they all possess the same amplitude and frequency?

A

True

44
Q

T or F

With transmission electron microscopy the beam of electrons passes through the specimen?

A

True

45
Q

T or F

SEM relies on electron backscattering?

A

True

46
Q

T or F

SPM does not produce a 3-D topographical map of a substance?

A

False

47
Q

Grain size may be specified by?

A

Average grain diameter.

48
Q

Give some examples of structure insensitive properties.

A
  1. Elastic constants
  2. melting points
  3. Density
  4. specific heat
  5. Coefficient of thermal expansion
49
Q

Give some examples of structure-sensitive properties.

A
  1. Electrical conductivity.
  2. Semi-conductive properties.
  3. Yield strength
  4. Fracture strength
  5. Creep strength
50
Q

Point defects include…

A
  1. Vacancy atoms
  2. Interstitial atoms
  3. Substitutional atoms

“Very Interesting Snakes.”

51
Q

Area defects include…

A
  1. Grain boundaries

2. Stacking faults

52
Q

Line Defects include…

A

Dislocations.

53
Q

Volume defects include…

A
  1. Pores

2. Cracks

54
Q

Low density in grain boundaries results in what three properties?

A
  1. High mobility
  2. High diffusivity
  3. High chemical reactivity

“H cubed MDC”

55
Q

Describe the difference between a vacancy and a self-interstitial.

A

A vacancy is an empty atomic site in a structure. An interstitial is the structural opposite. An extra atom is positioned between atomic sites.

56
Q

T or F

Graphene tends to loosely pack?

A

True

57
Q

T or F

Self-interstitials are much more likely in metals.

A

False, since atoms are very closely packed in metals it takes a lot of energy to squeeze an atom into space that’s already occupied.

58
Q

The presence of vacancies increases the ___ of the material.

A

Entropy.

59
Q

T or F
A solid solution is compositionally homogeneous, and impurity atoms are randomly and uniformly scatter throughout the solid.

A

True

60
Q

What two impurity defects are found in solid solutions?

A
  1. Substitutional

2. Interstitial

61
Q

Describe a substitutional impurity defect with respect to solid solutions.

A

For the substitutional type, solute or impurity atoms replace or substitute for the host atoms.

Extra Notes: Several features of the solute and solvent atoms determine the degree to which the former dissolves in the latter. These are expressed as four Hume–Rothery rules.

62
Q

Mixed Dislocations are a combination of what?

A

Both edge and screw dislocations.

Material Science (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions