69
Materials Science Regina Zibuck [email protected] Please note – This presentation was given at a 2012-2013 workshop. Be sure to refer to the 2013-2014 event rules for any changes.
Materials Science
Regina Zibuck
Please note – This presentation was given at a 2012-2013
workshop. Be sure to refer to the 2013-2014 event rules
for any changes.
Disclaimer
• I am not the event supervisor
• I do not know what the event supervisor will cover
• I am not a Materials Chemist
• I am an Organic Chemist
Properties of Materials (Materials Chemistry)
• Evaluating the intermolecular forces of materials
– Crystal structure
• Ionic, covalent, crystalline, semi-crystalline, amorphous
• Cubic – FCC, BCC, HCP, simple cubic
– Surface chemistry
• Surface tension
• Contact angle
• Thickness of a molecule or film
Properties of Materials (Materials Chemistry)
• Evaluating the mechanical performance of materials
– Visual
– Stiffness
– Yield strength
– Surface area/volume ratio
– Creep rate
– Viscosity
Resources
• soinc.org
• AP Chem textbook, chapters on bonding, liquids and solids
• Materials Science textbook
• http://www.uwstout.edu/chemistry/scienceolympiad.cfm
• The internet, search key words
6
Types of Materials • Metals:
– Strong, ductile
– High thermal & electrical conductivity
– Opaque, reflective.
• Polymers/plastics: Covalent bonding sharing of e’s
– Soft, ductile, low strength, low density
– Thermal & electrical insulators
– Optically translucent or transparent.
• Ceramics: ionic bonding (refractory) – compounds of metallic & non-metallic elements (oxides, carbides, nitrides, sulfides)
– Brittle, glassy, elastic
– Non-conducting (insulators)
7
1. Pick Application Determine required Properties
Processing: changes structure and overall shape ex: casting, sintering, vapor deposition, doping forming, joining, annealing.
Properties: mechanical, electrical, thermal, magnetic, optical, deteriorative.
Material: structure, composition.
2. Properties Identify candidate Material(s)
3. Material Identify required Processing
The Materials Selection Process
8
ELECTRICAL • Electrical Resistivity of Copper:
• Adding “impurity” atoms to Cu increases resistivity.
• Deforming Cu increases resistivity.
Adapted from Fig. 18.8, Callister & Rethwisch 8e. (Fig. 18.8 adapted from: J.O. Linde, Ann Physik 5, 219 (1932); and C.A. Wert and R.M. Thomson, Physics of Solids, 2nd edition, McGraw-Hill Company, New York, 1970.)
T (ºC) -200 -100 0
1
2
3
4
5
6
Res
isti
vity
, r
(10
-8 O
hm
-m)
0
9
THERMAL • Space Shuttle Tiles:
-- Silica fiber insulation offers low heat conduction.
• Thermal Conductivity
of Copper: -- It decreases when you add zinc!
Adapted from Fig. 19.4W, Callister 6e. (Courtesy of Lockheed Aerospace Ceramics Systems, Sunnyvale, CA) (Note: "W" denotes fig. is on CD-ROM.)
Adapted from Fig. 19.4, Callister & Rethwisch 8e. (Fig. 19.4 is adapted from Metals Handbook: Properties and Selection: Nonferrous alloys and Pure Metals, Vol. 2, 9th ed., H. Baker, (Managing Editor), American Society for Metals, 1979, p. 315.)
Composition (wt% Zinc) Th
erm
al C
on
du
ctiv
ity
(W
/m-K
)
400
300
200
100
0 0 10 20 30 40
100 mm
Adapted from chapter-opening photograph, Chapter 17, Callister & Rethwisch 3e. (Courtesy of Lockheed Missiles and Space Company, Inc.)
10
MAGNETIC • Magnetic Permeability
vs. Composition:
-- Adding 3 atomic % Si makes Fe a better recording medium!
Adapted from C.R. Barrett, W.D. Nix, and A.S. Tetelman, The Principles of Engineering Materials, Fig. 1-7(a), p. 9, 1973. Electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.
Fig. 20.23, Callister & Rethwisch 8e.
• Magnetic Storage:
-- Recording medium is magnetized by recording head.
Magnetic Field M
agn
etiz
atio
n
Fe+3%Si
Fe
11
• Transmittance:
-- Aluminum oxide may be transparent, translucent, or opaque depending on the material structure.
Adapted from Fig. 1.2, Callister & Rethwisch 8e. (Specimen preparation, P.A. Lessing; photo by S. Tanner.)
single crystal polycrystal: low porosity
polycrystal: high porosity
OPTICAL
12
DETERIORATIVE • Stress & Saltwater...
-- causes cracks!
Adapted from chapter-opening photograph, Chapter 16, Callister & Rethwisch 3e. (from Marine Corrosion, Causes, and Prevention, John Wiley and Sons, Inc., 1975.) 4 mm -- material:
7150-T651 Al "alloy" (Zn,Cu,Mg,Zr)
Adapted from Fig. 11.26, Callister & Rethwisch 8e. (Provided courtesy of G.H. Narayanan and A.G. Miller, Boeing Commercial Airplane Company.)
• Heat treatment: slows crack speed in salt water!
Adapted from Fig. 11.20(b), R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials" (4th ed.), p. 505, John Wiley and Sons, 1996. (Original source: Markus O. Speidel, Brown Boveri Co.)
“held at 160ºC for 1 hr before testing”
increasing load crac
k sp
ee
d (
m/s
) “as-is”
10 -10
10 -8
Alloy 7178 tested in saturated aqueous NaCl solution at 23ºC
13
• Occurs between + and - ions.
• Requires electron transfer.
• Large difference in electronegativity required.
• Example: NaCl
Ionic Bonding
Na (metal)
unstable
Cl (nonmetal)
unstable
electron
+ - Coulombic
Attraction
Na (cation)
stable
Cl (anion)
stable
14
Ionic Bonding • Energy – minimum energy most stable
– Energy balance of attractive and repulsive terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig. 2.8(b), Callister & Rethwisch 8e.
15
C: has 4 valence e-, needs 4 more
H: has 1 valence e-, needs 1 more
Electronegativities are comparable.
Adapted from Fig. 2.10, Callister & Rethwisch 8e.
Covalent Bonding • similar electronegativity - share electrons
• bonds determined by valence – s & p orbitals dominate bonding
• Example: CH4
shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH 4
16
• atoms pack in periodic, 3D arrays
Crystalline materials...
-metals -many ceramics
-some polymers
• atoms have no periodic packing
Noncrystalline materials...
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 "Amorphous" = Noncrystalline Adapted from Fig. 3.23(b), Callister & Rethwisch 8e.
Adapted from Fig. 3.23(a), Callister & Rethwisch 8e.
Materials and Packing
Si Oxygen
• typical of:
• occurs for:
17
Metallic Crystal Structures
• How can we stack metal atoms to minimize empty space?
2-dimensions
vs.
Now stack these 2-D layers to make 3-D structures
18
• Tend to be densely packed.
• Reasons for dense packing:
- Typically, only one element is present, so all atomic radii are the same. - Metallic bonding is not directional. - Nearest neighbor distances tend to be small in order to lower bond energy. - Electron cloud shields cores from each other
• Have the simplest crystal structures.
We will examine three such structures...
Metallic Crystal Structures
19
• Rare due to low packing density (only Po has this structure) • Close-packed directions are cube edges.
• Coordination # = 6 (# nearest neighbors)
Simple Cubic Structure (SC)
(Courtesy P.M. Anderson)
20
• APF for a simple cubic structure = 0.52
APF =
a 3
4
3 p (0.5a) 3
1
atoms
unit cell
atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell*
Volume of unit cell
*assume hard spheres
Adapted from Fig. 3.24, Callister & Rethwisch 8e.
close-packed directions
a
R=0.5a
contains 8 x 1/8 = 1 atom/unit cell
21
• Coordination # = 8
Adapted from Fig. 3.2, Callister & Rethwisch 8e.
• Atoms touch each other along cube diagonals.
--Note: All atoms are identical; the center atom is shaded differently only for ease of viewing.
Body Centered Cubic Structure (BCC)
ex: Cr, W, Fe (), Tantalum, Molybdenum
2 atoms/unit cell: 1 center + 8 corners x 1/8 (Courtesy P.M. Anderson)
22
Atomic Packing Factor: BCC
a
APF =
4
3 p ( 3 a/4 ) 3
2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions:
3 a
• APF for a body-centered cubic structure = 0.68
a R Adapted from
Fig. 3.2(a), Callister & Rethwisch 8e.
a 2
a 3
23
• Coordination # = 12
Adapted from Fig. 3.1, Callister & Rethwisch 8e.
• Atoms touch each other along face diagonals.
--Note: All atoms are identical; the face-centered atoms are shaded differently only for ease of viewing.
Face Centered Cubic Structure (FCC)
ex: Al, Cu, Au, Pb, Ni, Pt, Ag
4 atoms/unit cell: 6 face x 1/2 + 8 corners x 1/8 (Courtesy P.M. Anderson)
24
• APF for a face-centered cubic structure = 0.74
Atomic Packing Factor: FCC
maximum achievable APF
APF =
4
3 p ( 2 a/4 ) 3
4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions:
length = 4R = 2 a
Unit cell contains:
6 x 1/2 + 8 x 1/8
= 4 atoms/unit cell a
2 a
Adapted from Fig. 3.1(a), Callister & Rethwisch 8e.
25
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
• ABCABC... Stacking Sequence • 2D Projection
• FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites
C C
C A
C C
C A
A
B C
26
• Coordination # = 12
• ABAB... Stacking Sequence
• APF = 0.74
• 3D Projection • 2D Projection
Adapted from Fig. 3.3(a), Callister & Rethwisch 8e.
Hexagonal Close-Packed Structure (HCP)
6 atoms/unit cell
ex: Cd, Mg, Ti, Zn
• c/a = 1.633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
27
Theoretical Density, r
where n = number of atoms/unit cell A = atomic weight VC = Volume of unit cell = a3 for cubic NA = Avogadro’s number = 6.022 x 1023 atoms/mol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
28
• Ex: Cr (BCC)
A = 52.00 g/mol
R = 0.125 nm
n = 2 atoms/unit cell
rtheoretical
a = 4R/ 3 = 0.2887 nm
ractual
a R
r = a3
52.00 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6.022 x 1023
Theoretical Density, r
= 7.18 g/cm3
= 7.19 g/cm3
Adapted from Fig. 3.2(a), Callister & Rethwisch 8e.
29
Densities of Material Classes r
metals > r ceramics > r
polymers
Why?
Data from Table B.1, Callister & Rethwisch, 8e.
r (
g/c
m )
3
Graphite/ Ceramics/ Semicond
Metals/ Alloys
Composites/ fibers
Polymers
1
2
2 0
30 B ased on data in Table B1, Callister
*GFRE, CFRE, & AFRE are Glass, Carbon, & Aramid Fiber-Reinforced Epoxy composites (values based on
60% volume fraction of aligned fibers in an epoxy matrix). 10
3
4
5
0.3
0.4 0.5
Magnesium
Aluminum
Steels
Titanium
Cu,Ni
Tin, Zinc
Silver, Mo
Tantalum Gold, W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE, PS PP, LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE *
CFRE *
GFRE*
Glass fibers
Carbon fibers
A ramid fibers
Metals have... • close-packing (metallic bonding) • often large atomic masses
Ceramics have... • less dense packing • often lighter elements
Polymers have... • low packing density (often amorphous) • lighter elements (C,H,O)
Composites have... • intermediate values
In general
Surface Chemistry
• Surface tension
• Contact angle
• Thickness of a molecule
Surface Tension
• A molecule in the interior of a liquid is attracted by the molecules surrounding it
Surface Tension
• Try to float a tack on water
• Add a drop of soap
Contact Angle
• The contact angle is the angle measured where a liquid interface meets a solid surface.
Material Performance and Characterization
• Visual
• Stiffness
• Yield strength
• Surface area/volume ratio
• Creep rate
• Viscosity
37
Microscopic Examination
• Crystallites (grains) and grain boundaries. Vary considerably in size. Can be quite large.
– ex: Large single crystal of quartz or diamond or Si
– ex: Aluminum light post or garbage can - see the individual grains
• Crystallites (grains) can be quite small (mm or less) – necessary to observe with a microscope.
38
• Useful up to 2000X magnification. • Polishing removes surface features (e.g., scratches) • Etching changes reflectance, depending on crystal orientation.
Micrograph of brass (a Cu-Zn alloy)
0.75mm
Optical Microscopy
Adapted from Fig. 4.13(b) and (c), Callister & Rethwisch 8e. (Fig. 4.13(c) is courtesy of J.E. Burke, General Electric Co.)
crystallographic planes
39
Grain boundaries...
• are imperfections, • are more susceptible to etching, • may be revealed as dark lines, • change in crystal orientation across boundary.
Adapted from Fig. 4.14(a) and (b), Callister & Rethwisch 8e. (Fig. 4.14(b) is courtesy of L.C. Smith and C. Brady, the National Bureau of Standards, Washington, DC [now the National Institute of Standards and Technology, Gaithersburg, MD].)
Optical Microscopy
ASTM grain size number
N = 2 n -1
number of grains/in2 at 100x magnification
Fe-Cr alloy
(b)
grain boundary
surface groove
polished surface
(a)
Unetched Steel 200 X
Etched Steel 200 X
Unetched Brass 200 X
Etched Brass 200 X
41
Optical Microscopy
• Polarized light
– metallographic scopes often use polarized light to increase contrast
– Also used for transparent samples such as polymers
42
Microscopy Optical resolution ca. 10-7 m = 0.1 mm = 100 nm
For higher resolution need higher frequency
– X-Rays? Difficult to focus.
– Electrons
• wavelengths ca. 3 pm (0.003 nm) – (Magnification - 1,000,000X)
• Atomic resolution possible
• Electron beam focused by magnetic lenses.
43
• Atoms can be arranged and imaged!
Carbon monoxide molecules arranged on
a platinum (111) surface.
Photos produced from the work of C.P. Lutz, Zeppenfeld, and D.M. Eigler. Reprinted with permission from International Business Machines Corporation, copyright 1995.
Iron atoms arranged on a copper (111) surface. These Kanji characters
represent the word “atom”.
Scanning Tunneling Microscopy (STM)
44
X-Ray Diffraction
• Diffraction gratings must have spacings comparable to the wavelength of diffracted radiation.
• Can’t resolve spacings
• Spacing is the distance between parallel planes of atoms.
45
X-Rays to Determine Crystal Structure
X-ray intensity (from detector)
q
q c
d = n
2 sin q c
Measurement of critical angle, qc, allows computation of planar spacing, d.
• Incoming X-rays diffract from crystal planes.
Adapted from Fig. 3.20, Callister & Rethwisch 8e.
reflections must be in phase for a detectable signal
spacing between planes
d
q
q extra distance travelled by wave “2”
46
Elastic means reversible!
Elastic Deformation 2. Small load
F
d
bonds stretch
1. Initial 3. Unload
return to initial
F
d
Linear- elastic
Non-Linear- elastic
47
Plastic means permanent!
Plastic Deformation (Metals)
F
d
linear elastic
linear elastic
d plastic
1. Initial 2. Small load 3. Unload
planes
still
sheared
F
d elastic + plastic
bonds
stretch
& planes
shear
d plastic
48
Stress has units: N/m2 or lbf /in2
Engineering Stress • Shear stress, t:
Area, Ao
F t
F t
F s
F
F
F s
t = F s
A o
• Tensile stress, s:
original area before loading
s = F t
A o 2 f
2 m
N or
in
lb =
Area, Ao
F t
F t
49
• Simple tension: cable
Note: t = M/AcR here.
Common States of Stress
o
s = F
A
o
t = F s
A
s s
M
M A o
2R
F s A c
• Torsion (a form of shear): drive shaft Ski lift (photo courtesy
P.M. Anderson)
A o = cross sectional
area (when unloaded)
F F
50
(photo courtesy P.M. Anderson) Canyon Bridge, Los Alamos, NM
o
s = F
A
• Simple compression:
Note: compressive structure member (s < 0 here). (photo courtesy P.M. Anderson)
OTHER COMMON STRESS STATES
A o
Balanced Rock, Arches National Park
51
• Tensile strain: • Lateral strain:
Strain is always dimensionless.
Engineering Strain
• Shear strain:
q
90º
90º - q y
x q g = x/y = tan
e = d
L o
Adapted from Fig. 6.1(a) and (c), Callister & Rethwisch 8e.
d /2
L o w o
- d e L = L
w o
d L /2
52
Stress-Strain Testing • Typical tensile test machine
Adapted from Fig. 6.3, Callister & Rethwisch 8e. (Fig. 6.3 is taken from H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, p. 2, John Wiley and Sons, New York, 1965.)
specimen extensometer
• Typical tensile specimen
Adapted from Fig. 6.2, Callister & Rethwisch 8e.
gauge length
53
Linear Elastic Properties
• Modulus of Elasticity, E: (also known as Young's modulus) Stress is proportional to strain; the ratio is constant Always the same for a given material As you apply load to a material, the strain increases constantly (or proportionately) with stress.
Hooke's Law:
s = E e s
Linear-
elastic
E
e
F
F simple tension test
Young’s Modulus
• http://www.matter.org.uk/schools/content/youngmodulus/default.htm
Example: In a tension test you apply a gradually increasing load to a sample. You can determine the amount of strain (e that occurs in a sample at any given stress level (s.
s (ksi) e (in/in x 0.001) 0 0 3 1 6 2 9 3 12 4
S
tre
ss ,s
(ksi)
Strain ,e (in/in x 0.001)
Knowing E for a given material and : E = s/e
1.) We can find how much stress is in the
material if we know the strain:
s = Ee
2.) We can find how much strain is in the material if we know the stress:
e= s E
• If the tension test continues, the stress will reach a level called the Proportional Limit ( sPL ). If the stress is increased above sPL , the strain will increase at a higher rate.
S
tre
ss (
s),
ksi
Strain (e), in/in
sPL
60
Metals Alloys
Graphite Ceramics Semicond
Polymers Composites
/fibers
E(GPa)
Based on data in Table B.2, Callister & Rethwisch 8e. Composite data based on reinforced epoxy with 60 vol% of aligned carbon (CFRE), aramid (AFRE), or glass (GFRE) fibers.
Young’s Moduli: Comparison
109 Pa
0.2
8
0.6
1
Magnesium,
Aluminum
Platinum
Silver, Gold
Tantalum
Zinc, Ti
Steel, Ni
Molybdenum
G raphite
Si crystal
Glass - soda
Concrete
Si nitride Al oxide
PC
Wood( grain)
AFRE( fibers) *
CFRE *
GFRE*
Glass fibers only
Carbon fibers only
A ramid fibers only
Epoxy only
0.4
0.8
2
4
6
10
2 0
4 0
6 0 8 0
10 0
2 00
6 00 8 00
10 00 1200
4 00
Tin
Cu alloys
Tungsten
<100>
<111>
Si carbide
Diamond
PTF E
HDP E
LDPE
PP
Polyester
PS PET
C FRE( fibers) *
G FRE( fibers)*
G FRE(|| fibers)*
A FRE(|| fibers)*
C FRE(|| fibers)*
61
• Stress at which noticeable plastic deformation has occurred.
when ep = 0.002
Yield Strength, sy
sy = yield strength
Note: for 2 inch sample
e = 0.002 = z/z
z = 0.004 in
Adapted from Fig. 6.10(a), Callister & Rethwisch 8e.
tensile stress, s
engineering strain, e
sy
ep = 0.002
62
Room temperature values
Based on data in Table B.4, Callister & Rethwisch 8e. a = annealed hr = hot rolled ag = aged cd = cold drawn cw = cold worked qt = quenched & tempered
Yield Strength : Comparison Graphite/ Ceramics/ Semicond
Metals/ Alloys
Composites/ fibers
Polymers
Yiel
d s
tren
gth
,
s y
(MPa
)
PVC
Har
d t
o m
easu
re
,
sin
ce in
ten
sio
n, f
ract
ure
usu
ally
occ
urs
bef
ore
yie
ld.
Nylon 6,6
LDPE
70
20
40
60 50
100
10
30
200
300
400
500 600 700
1000
2000
Tin (pure)
Al (6061) a
Al (6061) ag
Cu (71500) hr Ta (pure) Ti (pure) a Steel (1020) hr
Steel (1020) cd Steel (4140) a
Steel (4140) qt
Ti (5Al-2.5Sn) a W (pure)
Mo (pure) Cu (71500) cw
Har
d t
o m
easu
re,
in c
eram
ic m
atri
x an
d e
po
xy m
atri
x co
mp
osi
tes,
sin
ce
in t
ensi
on
, fra
ctu
re u
sual
ly o
ccu
rs b
efo
re y
ield
.
H DPE PP
humid
dry
PC
PET
¨
Surface Area/Volume Ratio
• The amount of surface area per unit volume of an object
• For a given shape, SA:V is inversely proportional to size
• Material with a large surface area to volume ratio reacts at a much faster rate than monolithic materials
Surface Area/Volume Ratio
65
Creep Sample deformation at a constant stress (s) vs. time
Adapted from
Fig. 8.28, Callister &
Rethwisch 8e.
Primary Creep: slope (creep rate)
decreases with time.
Secondary Creep: steady-state
i.e., constant slope (e/t).
Tertiary Creep: slope (creep rate)
increases with time, i.e. acceleration of rate.
s s,e
0 t
66
• Occurs at elevated temperature, T > 0.4 Tm (in K)
Adapted from Fig. 8.29,
Callister & Rethwisch 8e.
Creep: Temperature Dependence
elastic
primary secondary
tertiary
67
Secondary Creep • Strain rate is constant at a given T, s
-- strain hardening is balanced by recovery
stress exponent (material parameter)
strain rate
activation energy for creep
(material parameter)
applied stress material const.
• Strain rate
increases
with increasing
T, s
10
2 0
4 0
10 0
2 0 0
10 -2 10 -1 1 Steady state creep rate (%/1000hr) e
s
Str
ess (
MP
a) 427ºC
538ºC
649ºC
Adapted from
Fig. 8.31, Callister 7e.
(Fig. 8.31 is from Metals
Handbook: Properties
and Selection:
Stainless Steels, Tool
Materials, and Special
Purpose Metals, Vol. 3,
9th ed., D. Benjamin
(Senior Ed.), American
Society for Metals,
1980, p. 131.)
-s=e
RT
QK cn
s exp2
Creep Failure • Failure: along grain boundaries.
applied
stress
g.b. cavities
From V.J. Colangelo and F.A. Heiser, Analysis of
Metallurgical Failures (2nd ed.), Fig. 4.32, p. 87, John
Wiley and Sons, Inc., 1987. (Orig. source: Pergamon
Press, Inc.)
68
Viscosity
• Resistance offered by a fluid due to the attraction of the molecules to each other
• Measure the time required for a constant volume of liquid to drain from a pipet
• http://chemmovies.unl.edu/chemistry/smallscale/SS070.html
