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midterm Flashcards

1
Q

What is an edge dislocation

A

a linear deffect that centers on the line that is defined along the edge of extra half plane of atoms

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2
Q

How does dislocations disappear

A

by annealing (increasing temperature)

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3
Q

What is a dislocation and what effects does it have

A

an extra or missing half plane that causes lattice distortion and crystal energy

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4
Q

What are line defects 1d?

A

Dislocations

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5
Q

What is a substitutional defect

A

when an impurity atom replaces host atom. requieres same crystal structure

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6
Q

What is an interstitial defect

A

when an atom occupies a space outside a latice position

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7
Q

what does vacancy cause

A

substitutional difussion in solids

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8
Q

what causes vacancy?

A

temperature increase increases vacancy concentration

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9
Q

what is vacancy

A

a lattice position with a missing atom

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10
Q

types of point defects

A

Vacancy

interstitial atom

substitutional atom

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11
Q

what are the types of defects

A

point defects 0d

line defects 1d

surface defects 2d

bulk defects 3d

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12
Q

What is a defect

A

a deviation from a perfect crystal. does not imply negative effect on properties

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13
Q

What is a lattice

A

an array of atoms that have some sort of symmetry

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14
Q

what is the lattice parameter (a)

A

length of one side of unit cell in terms of atomic radii

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15
Q

bonds in organic materials

A

hydreogen, covalent , van der waals

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16
Q

bonds in metals

A

metallic

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17
Q

bonds in ceramic/glass

A

ionic

covalent

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18
Q

in Interatomic potential curve what does a more assymetrical curve represent

A

higher thermal expansion coefficient

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19
Q

in Interatomic potential curve what is a higher curvature associated with?

A

higher elastic modulus

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20
Q

What is higher bonding energy associated with

A

higher melting temp

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21
Q

How do you get to energy from a force value?

A

its integral with respect to r (F dr)

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22
Q

What does repulsive forces depend on

A

interactions of negatively charged electron clouds

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23
Q

What does attractive forces depend on?

A

nature of atomic bond

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24
Q

What are the types of bonding forces and energy

A

Attractive and repulsive

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25
What is ultimate tensile stregnth?
max stress in stress-strain curve
26
What is yielding caused by microscopically?
crystal shear
27
Plastic deformation
non-reversible deformation. Occurs whne stress exceeds "yiled strength"
28
types of stress/strain
tensile compressive shear torsion
29
Youngs modulus
ratio between stress and strain
30
material properties examples
density elastic modulus toughness thermal conductivity magneticity
31
extensive property
physical attribute depends on size and matter
32
intensive property
behaviour of material does not depend on size or amount ofmatter
33
what is a screw dislocation
lattice strucutre distorted in a helical matter
34
Mixed dislocation
superposition of edge and screw
35
effects of dislocations on materials
change shape strength changes based on how easy dislocations moves electrical conductivity
36
What is the difference between external surfaces and bulk in planar defects?
surface atoms have higher energy than bulk atoms due to dangling bonds
37
Planar defects (grain boundaries)
grains are separated by transition regions, and the atomic mismatch creates grain boundaries
38
What are some examples of bulk defects?
voids porosity cracks
39
What is a phase
local arrangement of matter which is physically distinct, chemically uniform, mechanically inseparable
40
What is distinct in a Binary Isomorphous phase diagram
Complete solubility of two components in the solid state
41
Eutectic phase diagram
limited solubility of two components in the solid state
42
Liquidus line
when liquid turns into a mixture of slush
43
solidus line
condition when slush turns into a solid
44
tie line
isothermal line that connects composition of two phases used in two phase regions
45
What phase transfroms into what in eutectic reaction
1 liquid to 2 solids
46
What phase transfroms into what in eutectoid reaction
1 solid to 2 solids
47
What phase transfroms into what in peritectic reaction
1 solid + 1 liquid to 1 solid
48
Eutectic point
point where liquid transforms directly to a oslid
49
What is the region left of eutectic point called?
hypoeutectic
50
what is the name of the region right of eutectic point?
hypereutectic
51
Work hardening/strain hardening
material stretched past yield strength
52
Where do dislocations prefet to glide
perpendicual to plane of highest interplanar spacing
53
why are FCC and BCC more ductile
more crystal symmetry increasing active slip planes making dislocations easier to move.
54
how does strain hardening occur?
dislocations occuring in plastic deformation that hinder the movement of other dislocations making the solid harder
55
In what way do Dislocation interact (distort) each other depending on their signs?
if distortions have same sign they repel each other, if they have opposite they annihilate each other
56
What causes Cold Working
caused by dislocation mulitiplication
57
Why/How does grain boundary strengthening work?
misorientation between grains restricts dislocation movement which needs rearrangement (producing force) that strengthens material. Also piles up dislocations making them repel each other also strengthening material
58
What is solid solution strengthening
when we introduce impurities of alloying element into a phase, and the atoms impose lattice strain in host atoms, hindering dislocation movement
59
What is precipitation hardening
Heating alloy into solutionized state, then rapidly cool it to room temperature allowing to form complex shapes, and then reheat to defrost microstructure
60
how does precipitation hardening work?
hinders dislocation motion and creates more dislocations
61
What is stress concentration and how does it occur?
if solid has elipitical crack, crack will impose a stress concentration.
62
What is the stress concentration factor kt
the ratio of highest stress to a reference applied stress of the gross cross-section
63
What is necking and what causes it?
When stretching a material, defects act as stress concentrators, debonding with the solid making voids and forming a neck. making structure weaker and induceing structure failure
64
Explain Brittle failure: Fracture Toughness Kic
in a crack, as the stress intencity Ki increases (with applied stress) it will reach critical value Kic where brittle fracture will occur.
65
How can stresss intencity increase
increase applied stress or crack length
66
What does fatigue mean for a material?
even if a material is loaded below yield strength, fatigue will make it eventually fracture
67
How does mean stress and yield strength affect fatigue strenght
increasing yield strength increases fatigue strength while increasing mean stress decreases fatigue strength
68
how does crack nucleation occur?
protrusions (sticking out) on the surface of crystals known as PSB act as stress concentrators which can lead to fatigue crack growth
69
Electrons in the __ band can excape their host atoms?
conduction band
70
if the band is partially full or they overlap we have an ___
electrical conductor
71
if the valence band is full and conduction band is empty we have a __
insulator or semiconductor
72
if the band gap is above 4 eV we have a __
insulator
73
what happens to electrons during scattering?
-loose Kinetic energy -changes direction of motion
74
How does scattering affect electric current?
causes resistance
75
What is drift velocity
the average electron velocity in the opposite dirrection of the electric field
76
What direction do free electrons move to when an electric field is applied?
opposite to the direction of the field
77
What does the resisitivity of a metal dependent on?
-temperature -composition -degree of cold work (dislocation density)
78
what is a dipole moment?
a vector that is directed from the negative to the positive charge
79
Whaat causes a material to polarize more?
more dipole moments
80
What are the types of polarization?
-electronic -ionic -orientation
81
What is electronic polarization?
displacement of the electron cloud by an electric field
82
What is ionic polarization?
displacement of ionic atoms in a lattice
83
What is orientation polarization?
alignment of polar molecules
84
What are the two types of semiconductors? and explain them
-Intrinsic: electrical behaviour depends on the properties of the pure material -extrinsic: electrical behaviour is dictated by dopants
85
What happens to conductivity as the band gap (Eg) increases?
decreases
86
What is a p-type semiconductor?
a semiconductor with excess electrons
87
What is an n-type semiconductor?
a semiconductor with excess holes where an electron could exists
88
What is the fermi function?
a thermal dynamic expression that describes the probability of an electron occupying a given energy level
89
What is the fermi level (Ef)?
the energy level with a 50% chance of being occupied by an electron
90
What is a band gap?
an energy band that can't be occupied by an electron
91
What is heat capacity (C)?
a material's ability to absorb heat from surroundings. Represents the amount of energy required produce a unit temperature rise (j/k)
92

mech 285 (1 decks)

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