Exam 2 Flashcards
(181 cards)
1
Q
How to increase strength in materials by 5-30% ?
A
Solution Hardening
Alloying & Grain Size Control
2
Q
How to increase strength in materials by 50-300% ?
A
Strain Hardening
Heat Treatment
3
Q
When a material is plastically deformed by
Strain Hardening / Work Hardening
Yield, Tensile, Hardness strength ________ but Ductility ________
A
increases
decreases
4
Q
Fully strain-hardened material yield strengths increase from ______ and tensile strengths increase _______
A
100-500%
50-100%
5
Q
Dislocations and brittleness can be removed with new strain-free grains by _______ the material.
A
heating
6
Q
___________ can be induced by rolling a polycrystalline metal
A
Anisotropy
7
Q
In isotropic materials. _____________
A
grains are equiaxed & randomly oriented
8
Q
Rolling in anisotropic materials affects ______
A
grain orientation and shape
9
Q
Stronger material have more _____________
A
dislocations
10
Q
Too many dislocations may lead to ___________
A
cracking
11
Q
For Strain Hardening, Strength is higher at the _______ than the ________
A
surface
center
12
Q
Why is Strain Hardening desirable?
A
Wear and high stresses at surface
13
Q
How is metal cold worked?
A
by forging, stamping or rolling
14
Q
Cold working does what to metal?
A
permanently changes its shape, (DEFORMED)
15
Q
What allows for the overall change in shape of the metal?
A
dislocations or slips in the grain structure
16
Q
How is warm working done?
A
same cold working process performed below recrystallization temperature but above room temperature
17
Q
What does warm working accomplish?
A
Reduces the mechanical energy to deform
18
Q
What is cold working?
A
working of material below its recrystallization temperature
19
Q
What is Annealing?
A
used to remove effects of cold working (heat and then slow cooling to soften materials)
20
Q
What is hot working?
A
working of material above its recrystallization temperature
21
Q
During hot working, _________
A
material recrystallizes immediately – no strain hardening builds up
22
Q
What is the advantage of hot working?
A
less forces required to deform material
23
Q
What are the disadvantages of hot working?
A
High temp may oxidize surface
Dimensions harder to control
Tolerances harder to control
24
Q
What happens during Recrystallization?
A
• New grains form that:
- - have low dislocation densities - - are small in size - - consume and replace parent cold-worked grains
25
All grains in cold-worked material have been _________
consumed/replaced
26
What are the effects of cold working?
```
Yield strength (YS) increases.
Tensile strength (TS) increases.
Ductility (%EL or %AR) decreases.
```
27
Strength is _______ by making dislocation
| motion difficult.
increased
28
How to strengthen materials?
Dislocations
29
The ability of a metal to plastically deform depends on _________
the ability of dislocations to move
30
Restricting dislocation motion leads to
harder & stronger material
31
Grain boundary:
Point defect:
Dislocation:
Second phase:
grain size reduction
solid solution strengthening
strain hardening (cold work)
precipitation hardening
32
In the Plastic Deformation of Polycrystalline Materials, Because of the random crystallographic orientations of the different grains
the direction of slip varies from one grain to another.
33
During deformation, mechanical integrity is maintained along the
grain boundaries
34
Each individual grain is _________ to some degree by its neighboring grains
constrained
35
solute or impurity atoms replace or substitute for the host atoms
Substitutional Solid Solution
36
impurity atoms fill the voids or interstitials among host atoms
Interstitial Solid Solution
- Small interstitial positions
- Atomic size of an interstitial impurity must be small (H, N, & C).
37
completely soluble in one another at all proportions
Cu-Ni (SSS)
38
Solid Solution Hardening is also
alloying
39
What is the Solid Solution Hardening Technique?
adding atoms of one element (the alloying element) to the crystalline lattice of another element (the base metal)
40
Solvent is defined as
the base substance, wherein the solute is being dissolved
41
A solute is a
substance that is dissolved into the solvent
42
When both elements exist in the same ________, both elements in their pure form “should” be of the same __________ (for complete solubility)
crystalline lattice
| crystal structure
43
Solvent and solute atoms must differ in ________ by less than __%
atomic size
| 15%
44
Strength is Solid Solution Hardening is dependent on
on ease of achieving dislocations in crystal lattice
45
Dislocations create ________ within material
stress fields
46
What is the process of Solid Solution Hardening?
Solute atoms introduced, then local stress fields are formed that interact with the dislocations, impeding their motion and causing an increase in the yield stress - increase in strength
47
Solute and solvent atoms differ in
size, local stress fields created
48
If the Solute atom size larger than solvent then____
field is compressive
49
If the Solute atoms are smaller than solvent atoms_____
field is tensile
50
Alloying with impurities form _______ or _______ solid solution.
Interstitial
| substitutional
51
Impurity atoms _______
distort the lattice & generate stress
52
______ can produce a barrier to dislocation motion
Stress
53
Small impurities tend to concentrate at ________
dislocations (regions of compressive strains)
54
partial cancellation of dislocation compressive strains and impurity atom tensile strains
regions of compressive strains
55
Solid Solution Alloying_________ of dislocations and _______ strength
reduces mobility
| increase
56
Large impurities tend to concentrate at __________
dislocations (regions of tensile strains)
57
Substitutional Rules: Conditions for substitutional solid solution
1. Δr (atomic radius) < 15%
2. Same crystal structure for pure metals
3. Proximity in periodic table
i.e., similar electronegativities
4. Valency – “should” be identical
All else being equal, a (solvent) metal will have a greater tendency to dissolve a (solute) metal of higher valency than one of lower valency.
58
solute or impurity atoms replace or substitute for the host atoms
Substitutional Defects
59
Metals have a ___________
crystalline structure
60
When metal solidifies from the molten state
millions of tiny crystals start to grow
61
The longer metal takes to cool, _______
the larger the crystals grow
62
These crystals form the ______ in the solid metal
grains
63
Each grain is a distinct _____l with its own ________
crystal
| orientation
64
adjacent grain planes at different orientations
Grain boundaries
65
Grain boundaries_________
prevent slip or makes slip more difficult
66
Slip occurs along a ______ of one atom
plane
67
Numerous grains ________
reduce amount of slip
68
When grain size decreases ______
strength increases
69
Strength is ________ related to grain area
inversely
70
Optical Microscopy is _________
Useful up to 2000X magnification
71
What is the Interception Method?
Draw a number of straight lines of same length so that the total interception of the lines with grain boundaries should be > 50
72
Atoms are bonded ________ along a grain boundary
less regularly
73
Energy is a function of the degree of _________, being ______for high-angle boundaries
misorientation
| larger
74
The atoms are bonded ________ along a grain boundary
less regularly
75
Greater disorder leads to
grain boundary energy
76
More reactive_______
makes etching possible
77
Impurity segregation _________
affecting the materials properties
78
As the metal solidifies, __________ start to form first
small crystal nuclei
79
Upon completion of solidification, the colonies contact each other, forming _________
grain boundaries
80
What are grain boundaries?
Boundaries between crystals in a polycrystalline material
81
There is a change in __________ across grain boundaries
crystal orientation
82
Grain boundary hinders the dislocation motion or acts as a barrier to _________ motion (slip)
dislocation
83
A ___________ material is harder and stronger than one that is coarse grained, as more _______ are acting to block dislocation movement
finer-grained
| barriers
84
Grain size reduction improves not only ________, but also the ________ of many alloys
strength
| toughness
85
Defects affect _________
material properties
86
A knowledge and understanding of phase diagrams is important to the engineer as they relate to the design and control of ________
heat treating processes
87
What is the Solubility Limit?
Max concentration for which only a solution occurs
88
Solubility limit ________ with Temperature
increases
89
In SSS Atoms of the parent metal (or solvent metal) are _______ or ________ by atoms of the alloying metal (solute metal)
replaced
| substituted
90
In SSS The atoms of the two metals in the alloy are of _______ size
similar
91
In ISS The atoms of the parent or solvent metal are _____ than the atoms of the alloying or solute metal
bigger
92
In ISS The smaller solute atoms fit into _________ or spaces between the large atoms
interstitial sites
93
For many alloy systems and at some specific temperature, there is a _________ of solute atoms that may dissolve in the solvent to form a _______
maximum concentration
| solid solution
94
a homogeneous portion of a system that has uniform physical and chemical characteristics
phase
95
If more than one phase is present in a given system, each will have its own ________
distinct properties
96
A boundary separating the _____ exists across which there will be a discontinuous and abrupt change in ________
phases
| physical and/or chemical characteristics
97
The physically and chemically distinct material regions that result
Phases in Materials
98
Solid solutions are commonly designated by
lowercase Greek letters (a , b, g, etc.)
99
Equilibrium conditions may be defined
as slow heating and/or cooling of the many materials to permit any phase change to occur
100
The relationships between ________ and the _______ & the quantities of phases at equilibrium
temperature
| compositions
101
For a binary system of known composition (C0) & temperature (T) that is at equilibrium, the following information can be obtained from the phase diagram:
The phases that are present
The composition of each phase
The amount (or percentage) of each phase
102
Line indicates the temperature at which the first solid appears upon cooling and the temperature at which the last solid disappears on heating. In few instances liquid separates into two liquids, the temperature at which the separation starts.
Liquidus Line
103
Line indicates temperature at which the last liquid disappears upon cooling.
Solidus Line
104
The line indicates the solubility limits
Solvus line
105
Line connecting three phases that are in equilibrium at a specific temperature in a binary system. Appears as a horizontal line because at constant temperature.
Invariant Reaction Line
106
connects the phases in equilibrium with each other – also sometimes called an isotherm
Tie line
107
liquid transforms to two solid phases
Eutectic
108
one solid phase transforms to two other solid phases
Eutectoid
109
liquid and one solid phase transform to a second solid phase
Peritectic
110
In a Eutectic Reaction, Upon cooling, _______ phase is transformed into the _______ phases (a and b) at the ______ temperature TE; upon heating, the opposite reaction occurs
one liquid
two solid
eutectic
111
For alloy of composition
C0 = CE
112
In a Eutectoid Reaction, Upon cooling, _____ phase is transformed into the ______ phases at the _____ temperature TE; upon heating, the opposite reaction occurs
one solid
two solid
eutectoid
113
one liquid phase transforms into two solid phase at a constant temperature
Eutectic reaction
114
one solid phase transforms into two solid phase at a constant temperature
Eutectoid reaction
115
Both steels and cast irons, primary structural materials in every technologically advanced culture, are essentially
iron-carbon alloys
116
the art and science of controlling thermal energy for the purpose of altering the properties of metals and alloys
Thermal processing or heat treating
117
a-Fe
Ferrite
118
y-Fe
Austenite
119
iron carbide Fe3C
Cementite
120
Pure Fe (room temperature to 912C), a single-phase BCC solid solution
Ferrite
121
a single-phase FCC solid solution (a ferrite transforms from BCC to FCC at 912C)
Austenite
122
The maximum solubility of carbon in austenite
2.14 wt% at 1147C.
123
Austenite is not stable below ______
727 degrees
124
intermediate phase with the chemical formula Fe3C
Cementite
125
Cementite is
brittle and hard
126
One eutectic reaction exists for the iron-iron carbide system,
at 4.30 wt% C and 1147C
127
One eutectoid reaction exists for the iron-iron carbide system
at 0.76 wt% C and 727C
128
The microstructure of the eutectoid steel that is slowly cooled consists of alternating layer or lamellae of the two phases (ferrite and cementite) that form simultaneously during the transformation
Pearlite
129
The thick light layers are the ______ phase, and the ______ phase appears as thin lamellae most of which appear dark
ferrite
| cementite
130
Pure iron
From the phase diagram, it is composed almost exclusively of the ferrite phase at room temperature
131
Steels
In most steels the microstructure consists of both a and Fe3C phases.
Carbon concentrations in commercial steels rarely exceed 1.0 wt%.
132
Cast irons
Commercial cast irons normally contain less than 4.5 wt% C.
133
Phase diagrams are useful tools to determine:
-the number and types of phases
-and the composition of each phase
for a given T and composition of the system
134
one liquid phase transforms into two solid phase at a constant temperature
Eutectic reaction
135
one solid phase transforms into two solid phase at a constant temperature
Eutectoid reaction
136
Steels and cast irons are based on binary Fe-C system and offer a wide range of properties due to different microstructures
Hypoeutectoid & hypereutectoid steels
137
What are the Four strengthening mechanisms?
Grain size refinement
Solid-solution strengthening
Strain hardening
Precipitation hardening
138
The development of microstructure in both single- and two-phase alloys ordinarily involves some type of __________
phase transformation
139
an alteration in the number and/or character of the phases
phase transformation
140
The _________ is fundamental to the development of microstructures in steel alloys
eutectoid reaction
141
_______ is the microstructural product of this transformation
Pearlite
142
The percentage of the transformation product is related to the __________ and __________
holding temperature
| holding time
143
For Fe-C alloys with compositions other than eutectoid composition, a _________ phase (either ferrite or cementite) will coexist with ________
proeutectoid
| pearlite
144
Pearlite has mechanical properties between the soft, ductile ________ and the hard, brittle _______
ferrite
| cementite
145
a change in the number and/or character of the phases that constitute the microstructure of an alloy
Phase Transformation
146
Nucleation
formation of very small particles, or nuclei, of the new phase
147
favorable nucleation sites
imperfection sites,
| e.g. grain boundaries)
148
increase of the nuclei in size. Some volume of the parent phase disappears
Growth
149
The thickness of the ferrite/cementite layers in pearlite depends on the ___________
temperature
150
With decreasing temperature, the layers of pearlite become progressively __________
thinner
151
At temperatures just below eutectoid __________
relatively thick layers → coarse pearlite
152
In the vicinity of 540°C__________
relatively thin layers
| → fine pearlite
153
Pearlite forms above the nose ________; bainite forms below the nose ________
(540 ~ 727°C)
| (215 ~ 540°C)
154
Bainite consists of ______ and _______ phases
ferrite
| cementite
155
Bainite forms as ________ or _______, depending on the temperature of the transformation
needles
| plates
156
Unlike pearlitic transformation, martensitic transformation is _____________
instantaneous
157
The horizontal lines indicate that
- The transformation is independent of time;
| - It is a function only of the temperature to which the alloy is quenched or rapidly cooled.
158
What is the beginning of this Martensite transformation?
M(start)
159
Two other horizontal and dashed lines, labeled ______ and _____, indicate percentages of the austenite-to- martensite transformation.
M(50%)
| M(90%)
160
Martensite is formed when _______ Fe-C alloys are rapidly ________ (or quenched) to a relatively _____ temperature (in the vicinity of the ambient)
austenitized
cooled
low
161
A transformation product that is competitive with pearlite
Martensite
162
Martensite is a transformation of FCC to
BCT (body-centered tetragonal)
163
Martensite occurs _______
instantaneously → time-independent
164
The martensite grains ________ and grow at a very rapid rate
nucleate
165
< 0.6 wt%C,
| long/thin plates, side by side, aligned parallel to one another
Lath
166
> 0.6 wt%C,
lenticular or
platelike appearance
Lenticular
167
Cementite (Fe3C) is much ______ but more _____ than ferrite (α)
harder
| brittle
168
Fe3C ↑
⇒ strength↑, ductility↓
169
Fine pearlite is ______ and ______ than coarse pearlite but less ______
harder
stronger
ductile
170
Hardest and strongest, and most brittle
Martensite
171
Volume change in Martensite
crack formation during quenching
172
In the as-quenched state, martensite, in addition to being ______, is so _____ that it cannot be used for most applications
very hard
| brittle
173
Any internal stresses that may have been introduced during quenching have a _________ effect
weakening
174
The ductility and toughness of martensite may be enhanced and internal stresses relieved by a heat treatment know as
Tempering
175
Tempering is accomplished by
heating the martensitic steel to a temperature below the eutectoid (normally, between 200-650°C) for a specified time period to allow microstructure/ property change through diffusion
176
By diffusional processes: Martensite (BCT, single phase)_______
→ Tempered Martensite (α + Fe3C)
177
Tempered martensite may be nearly as hard and strong as martensite, but with substantially enhanced _______
& _________
ductility
| toughness
178
Tempered martensite consists of _________
extremely small cementite particles embedded within a ferrite matrix
179
_________ is involved in the transformation
Carbon diffusion
180
Heat treatment variables are _______
temperature and time
181
most treatments are
constant- temperature processes
