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경상대학교 Ceramic Design Lab.
경상대학교 Ceramic Design Lab.
ISSUES TO ADDRESS...
• How are metal alloys classified and how are they used?
• What are some of the common fabrication techniques?
• How do properties vary throughout a piece of material
that has been quenched, for example?
• How can properties be modified by post heat treatment?
Chapter 11: Structural Materials –
Metals, Ceramics, and Glasses
경상대학교 Ceramic Design Lab.
Taxonomy of Metals Metal Alloys
Steels
Ferrous Nonferrous
Cast Irons Cu Al Mg Ti
<1.4wt%C 3-4.5 wt%C
Steels <1.4 wt% C
Cast Irons 3-4.5 wt% C
Fe 3 C
cementite
1600
1400
1200
1000
800
600
400 0 1 2 3 4 5 6 6.7
L
g
austenite
g +L
g +Fe3C a
ferrite a +Fe3C
L+Fe3C
d
(Fe) Co , wt% C
Eutectic:
Eutectoid: 0.76
4.30
727°C
1148°C
T(°C) microstructure: ferrite, graphite cementite
경상대학교 Ceramic Design Lab.
Steels
Low Alloy High Alloy
low carbon <0.25 wt% C
Med carbon 0.25-0.6 wt% C
high carbon 0.6-1.4 wt% C
Uses auto struc. sheet
bridges towers press. vessels
crank shafts bolts hammers blades
pistons gears wear applic.
wear applic.
drills saws dies
high T applic. turbines furnaces V. corros. resistant
Example 1010 4310 1040 43 40 1095 4190 304
Additions none Cr,V Ni, Mo
none Cr, Ni Mo
none Cr, V, Mo, W
Cr, Ni, Mo
plain HSLA plain heat
treatable plain tool
austenitic stainless
Name
Hardenability 0 + + ++ ++ +++ 0 TS - 0 + ++ + ++ 0 EL + + 0 - - -- ++
increasing strength, cost, decreasing ductility
경상대학교 Ceramic Design Lab.
Refinement of Steel from Ore
Iron Ore Coke
Limestone
3CO + Fe2O3 2Fe +3CO2
C + O2 CO2
CO2 + C 2CO
CaCO3 CaO+CO2 CaO + SiO2 + Al2O3 slag
purification
reduction of iron ore to metal
heat generation
Molten iron
BLAST FURNACE
slag air
layers of coke
and iron ore
gas refractory
vessel
경상대학교 Ceramic Design Lab.
Ferrous Alloys
Iron containing – Steels - cast irons
Nomenclature AISI & SAE
10xx Plain Carbon Steels
11xx Plain Carbon Steels (resulfurized for machinability)
15xx Mn (10 ~ 20%)
40xx Mo (0.20 ~ 0.30%)
43xx Ni (1.65 - 2.00%), Cr (0.4 - 0.90%), Mo (0.2 - 0.3%)
44xx Mo (0.5%)
where xx is wt% C x 100
example: 1060 steel – plain carbon steel with 0.60 wt% C
Stainless Steel -- >11% Cr
경상대학교 Ceramic Design Lab.
TABLE 11.1 AISI–SAE Designation System for Carbon and Low-Alloy Steels
경상대학교 Ceramic Design Lab.
TABLE 11.1 (continued) AISI–SAE Designation System for Carbon and Low-Alloy Steels
경상대학교 Ceramic Design Lab.
Low-carbon ste el: less than about 0.25 wt% C, no martensite, cold work strengthening, Ferrite and pearlite microstrure
y = 275 MPa, =415-550 Mpa, 25% EL
High-strength, low-alloy (HSLA) steel contain other alloying elements such as Mn, P, Si, Ni, Mo in
combined concentration as high as 1 wt% Most may be strengthened by heat treatment, giving tensile
strength in execes of 480 Mpa.
Medium-carbon ste el: between about 0.25 and 0.60 wt% C, may be heat-treated by austenitizing, quenching, and then tempering to improve
their mechanical properties , They ate most often utilized in the tempered condition, having microsturtures of tempered martensite.
High-carbon steel: between about 0.60 and 1.4 wt% C, are the highest, strongest, and yet least ductile of the carbon steels. They are almost
always used in a hardened and tempered condition, as such, are specially wear resistant and capable of holding a sharp cutting edge. Alloys
containing Cr, V, Mo, W combine with carbon to form very hard and wear-resistant carbide compounds (e.g., Cr23C6, V4C3, and WC)
경상대학교 Ceramic Design Lab.
Stainless Steels
• Alloy steels containing at least 10% Cr are SS.
• Contain sufficient amount of Cr that they are considered high alloy.
• Corrosion resistance is imparted by the formation of a passivation
layer characterized by:
– Insoluble chromium oxide film on the surface of the metal - (Cr2O3) .
– Develops when exposed to oxygen and impervious to water and air.
– Layer is too thin to be visible
– Quickly reforms when damaged
– Susceptible to sensitization, pitting, crevice corrosion and acidic envir
onments.
– Passivation can be improved by adding nickel, molybdenum and vana
dium.
경상대학교 Ceramic Design Lab.
General Properties of Stainless Steels
• Electrical Resistivity
– Surface & bulk resistance is
higher than that for plain-
carbon steels
• Thermal Conductivity
– About 40 to 50 percent that of
plain-carbon steel
• Melting Temperature
– Plain-carbon:1480-1540 °C
– Martensitic: 1400-1530 °C
– Ferritic: 1400-1530 °C
– Austenitic: 1370-1450 °C
• Coefficient of Thermal
Expansion
– Greater coefficient than plain-
carbon steels
• High Strength
– Exhibit high strength at room and
elevated temperatures
• Surface Preparation
– Surface films must be removed
prior to welding
경상대학교 Ceramic Design Lab.
SS can also be classified by crystal structure (austenitic, ferritic, marten
sitic)
•Best corrosion resistance (CR): Austenitic (25% Cr)
•Middle CR : Ferritic (15% Cr),
•Least CR: Martensitic (12% Cr), but strongest
• Over 150 grades of SS available, usually categorized into 5 series
containing alloys w/ similar properties.
• AISI classes for SS:
– 200 series = chromium, nickel,manganese (austenitic)
– 300 series = chromium, nickel (austenitic)
– 400 series = chromium only (ferritic)
– 500 series = low chromium <12% (martensitic)
– 600 series = Precipitation hardened series (17-7PH, 15-5PH)
경상대학교 Ceramic Design Lab.
200/300 Series SS (Austenitic):
• Most common SS (roughly 70% of total SS production)
• Used for flatware, cookware, architecture, automotive, etc.
• 0.15% C (max), 16% Cr (min) and Ni or Manganese
• Austenitic, High strength, best corrosion resistance. High temp capability
up to 1200 F. non-magnetic, good ductility and toughness, not hardenable
by heat treatment, but they can be strengthened via cold working, best
corrosion resistance but most expensive, corrosive in hydrochloric acid.
• General use where corrosion resistance is needed.
• Typical alloy 18% Cr and 10% Ni = commonly known as 18/10 stainless
• Also have low carbon version of Austenitic SS (316L or 304L) used to avoid
corrosion problem caused by welding, L = carbon content < 0.03%
경상대학교 Ceramic Design Lab.
400 Series SS (Ferritic):
• Ferritic, Automotive trim, chemical processing, blades, knives,
springs, ball bearings, surgical instruments. Can be heat
treated!
• Contain between 10.5% and 27% Cr, little Ni and usually
molybdenum.
– Common grades: 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2Ni
• Magnetic (high in Fe content) and may rust due to iron
content.
• Lower strength vs 300 series austenitic grades
• Cheap
경상대학교 Ceramic Design Lab.
500 Series SS (Martensitic):
• Not as corrosion resistant as the other classes but extremely
strong and tough as well as machineable and can be
hardened via heat treat.
• High strength structural applications (Su up to 300 ksi) –
nuclear plants, ships, steel turbine blades, tools, etc.
• Magnetic
경상대학교 Ceramic Design Lab.
600 Series Precipitation Hardening Martensitic SS:
• Have corrosion resistance comporable to 300 series austentic
grades but can be precipitation hardened for increased
strength!
• Key: High strength + corrosion resistance BOTH.
• Why? Aerospace industry – defense budgets determined 2%
of GDP spent dealing with corrosion so developed high
strength corrosion resistant steel to replace alloy steels.
• Lockheed-Martin Joint Striker Fighter – 1st aircraft to use PH
SS for entire airframe.
• Common Grades: – 630 grade = 17-4 PH (17% Cr, 4% Ni),
– 17-4 PH,
– 15-5 PH
경상대학교 Ceramic Design Lab.
Cast Iron
• Ferrous alloys with > 2.1 wt% C
– more commonly 3 - 4.5 wt%C
• low melting (also brittle) so easiest to cast
• Cementite decomposes to ferrite + graphite
Fe3C 3 Fe (a) + C (graphite)
– generally a slow process
경상대학교 Ceramic Design Lab.
Fe-C True Equilibrium Diagram
Graphite formation
promoted by
• Si > 1 wt%
• slow cooling
1600
1400
1200
1000
800
600
400 0 1 2 3 4 90
L
g +L
a + Graphite
Liquid +
Graphite
(Fe) Co , wt% C
0.6
5 740°C
T(°C)
g + Graphite
100
1153°C g
Austenite 4.2 wt% C
a + g
경상대학교 Ceramic Design Lab.
Types of Cast Iron
Gray iron
• graphite flakes
• weak & brittle under tension
• stronger under compression
• excellent vibrational dampening
• wear resistant
Ductile iron
• add Mg or Ce
• graphite in nodules not flakes
• matrix often pearlite - better
ductility
경상대학교 Ceramic Design Lab.
Types of Cast Iron
White iron
• <1wt% Si so harder but brittle
• more cementite
Malleable iron
• heat treat at 800-900ºC
• graphite in rosettes
• more ductile
경상대학교 Ceramic Design Lab.
Ductile Iron
Malleable Iron Gray Iron
White Cast Iron
White cast iron Gray iron Ductile iron Malleable iron
Ferrous metallurgy
경상대학교 Ceramic Design Lab.
Production of Cast Iron
경상대학교 Ceramic Design Lab.
Limitations of Ferrous Alloys
1) Relatively high density
2) Relatively low conductivity
3) Poor corrosion resistance
경상대학교 Ceramic Design Lab.
Nonferrous Alloys
NonFerrous Alloys
• Al Alloys -lower r : 2.7g/cm3
-Cu, Mg, Si, Mn, Zn additions -solid sol. or precip. strengthened (struct.
aircraft parts & packaging)
• Mg Alloys -very low r : 1.7g/cm3
-ignites easily - aircraft, missiles
• Refractory metals -high melting T -Nb, Mo, W, Ta • Noble metals
-Ag, Au, Pt - oxid./corr. resistant
• Ti Alloys -lower r : 4.5g/cm3
vs 7.9 for steel -reactive at high T - space applic.
• Cu Alloys Brass: Zn is subst. impurity (costume jewelry, coins, corrosion resistant) Bronze : Sn, Al, Si, Ni are subst. impurity (bushings, landing gear) Cu-Be : precip. hardened for strength
경상대학교 Ceramic Design Lab.
Metal Fabrication
• How do we fabricate metals?
– Blacksmith - hammer (forged)
– Molding - cast
• Forming Operations
– Rough stock formed to final shape
Hot working vs. Cold working
• T high enough for • well below Tm
recrystallization • work hardening
• Larger deformations • smaller deformations
경상대학교 Ceramic Design Lab.
• Casting (Cast iron)
• Wrought processing
– Rolling
– Extrusion
– Forming
– Stamping
– Forging
– Drawing
• Joining
– Welding
– Brazing
– Soldering
• Powder metallurgy
• Hot isostatic pressing
• Superplastic forming
• Rapid solidification
• Additive manufacturing
Major processing methods for metals
경상대학교 Ceramic Design Lab.
FORMING
roll
A o
A d roll
• Rolling (Hot or Cold Rolling)
(I-beams, rails, sheet & plate)
A o A d
force
die
blank
force
• Forging (Hammering; Stamping)
(wrenches, crankshafts)
often at
elev. T
Metal Fabrication Methods - I
ram billet
container
container
force die holder
die
A o
A d extrusion
• Extrusion
(rods, tubing)
ductile metals, e.g. Cu, Al (hot)
tensile force
A o
A d die
die
• Drawing
(rods, wire, tubing)
die must be well lubricated & clean
CASTING JOINING
경상대학교 Ceramic Design Lab.
FORMING CASTING JOINING
Metal Fabrication Methods - II
• Casting- mold is filled with metal
– metal melted in furnace, perhaps alloying elements added. Then cast in a mold
– most common, cheapest method
– gives good production of shapes
– weaker products, internal defects
– good option for brittle materials
경상대학교 Ceramic Design Lab.
• Sand Casting
(large parts, e.g.,
auto engine blocks)
Metal Fabrication Methods - II
• trying to hold something that is hot
• what will withstand >1600ºC?
• cheap - easy to mold => sand!!!
• pack sand around form (pattern) of desired shape
Sand Sand
molten metal
FORMING CASTING JOINING
경상대학교 Ceramic Design Lab.
plaster
die formed
around wax
prototype
• Sand Casting
(large parts, e.g.,
auto engine blocks)
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
Metal Fabrication Methods - II
Investment Casting
• pattern is made from paraffin.
• mold made by encasing in plaster of paris
• melt the wax & the hollow mold is left
• pour in metal
wax
FORMING CASTING JOINING
Sand Sand
molten metal
경상대학교 Ceramic Design Lab.
plaster
die formed
around wax
prototype
• Sand Casting
(large parts, e.g.,
auto engine blocks)
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
Metal Fabrication Methods - II
wax
• Die Casting
(high volume, low T alloys)
• Continuous Casting
(simple slab shapes)
molten
solidified
FORMING CASTING JOINING
Sand Sand
molten metal
경상대학교 Ceramic Design Lab.
CASTING JOINING
Metal Fabrication Methods - III
• Powder Metallurgy
(materials w/low ductility)
pressure
heat
point contact
at low T
densification
by diffusion at
higher T
area contact
densify
• Welding
(when one large part is
impractical)
• Heat affected zone:
(region in which the
microstructure has been
changed).
piece 1 piece 2
fused base metal
filler metal (melted) base metal (melted)
unaffected unaffected heat affected zone
FORMING
경상대학교 Ceramic Design Lab.
Powder Metallurgy
경상대학교 Ceramic Design Lab.
Weakening by:
•Porosity (produced by casting, welding, or powder metallurgy)
•Annealing
•Hot-working
•Heat-affected zone (welding)
•Phase transformations (e.g., tempered martensite)
Strengthening by:
•Cold working
•Alloying (e.g., solution hardening)
•Phase transformations (e.g., martensitic)
General “Rules of Thumb” for properties of processed materials
경상대학교 Ceramic Design Lab.
Variation of the mechanical properties of copper–nickel alloys with composition
경상대학교 Ceramic Design Lab.
•The mechanical properties of two brass alloys vary with the degree of cold work
•Note the general tradeoff between strength and ductility.
경상대학교 Ceramic Design Lab.
Ceramics and Glasses
Three main categories:
- Crystalline Ceramics
- Glasses
- Glass-ceramics
경상대학교 Ceramic Design Lab.
• Properties: -- Tm for glass is moderate, but large for other ceramics.
-- Small toughness, ductility; large moduli & creep resist.
• Applications: -- High T, wear resistant, novel uses from charge neutrality.
• Fabrication -- some glasses can be easily formed
-- other ceramics can not be formed or cast.
Glasses Clay
products
Refractories Abrasives Cements Advanced
ceramics
-optical - composite
reinforce
- containers/
household
-whiteware - bricks
-bricks for
high T
(furnaces)
-sandpaper - cutting
- polishing
-composites - structural
engine - rotors
- valves
- bearings
-sensors
Adapted from Fig. 13.1 and discussion in
Section 13.2-6, Callister 7e.
Taxonomy of Ceramics
경상대학교 Ceramic Design Lab.
• Need a material to use in high temperature furnaces.
• Consider the Silica (SiO2) - Alumina (Al2O3) system.
• Phase diagram shows: mullite, alumina, and crystobalite as candidate refractories.
Application: Refractories
Composition (wt% alumina)
T(°C)
1400
1600
1800
2000
2200
20 40 60 80 100 0
alumina +
mullite
mullite + L
mullite Liquid
(L)
mullite + crystobalite
crystobalite + L
alumina + L
3Al2O3-2SiO2
경상대학교 Ceramic Design Lab.
ZrO2-CaO diagram:
경상대학교 Ceramic Design Lab.
• Example: Oxygen sensor ZrO2 • Principle: Make diffusion of ions
fast for rapid response.
Application: Sensors
A Ca 2+ impurity
removes a Zr 4+ and a
O 2 - ion.
Ca 2+
• Approach: Add Ca impurity to ZrO2: -- increases O2- vacancies
-- increases O2- diffusion rate
reference gas at fixed oxygen content
O 2-
diffusion
gas with an unknown, higher oxygen content
- + voltage difference produced!
sensor • Operation: -- voltage difference
produced when
O2- ions diffuse
from the external
surface of the sensor
to the reference gas.
경상대학교 Ceramic Design Lab.
TABLE 11.4 Compositionsa of Some Silicate Ceramics
경상대학교 Ceramic Design Lab.
Amorphous Silica
경상대학교 Ceramic Design Lab.
• Quartz is crystalline
SiO2:
• Basic Unit: • Glass is amorphous
• Amorphous structure occurs by adding impurities
(Na+,Mg2+,Ca2+, Al3+)
• Impurities: interfere with formation of
crystalline structure.
(soda glass)
Glass Structure
Si0 4 tetrahedron 4-
Si 4+
O 2 -
Si 4+
Na +
O 2 -
경상대학교 Ceramic Design Lab.
Glasses
Network modifiers: Oxides that breakup the
glass network.
Added to glass to increase workability.
Examples:- Na2O, K2O, CaO, MgO.
Oxygen atom enters network and other
ion stay in interstices.
Intermediate oxides: Cannot form glass
network by themselves but can join into an
existing network.
Added to obtain special properties.
Examples: Al2O3, Lead oxide.
Soda lime glass: Very common glass (90%). 71-73% SiO2,
12-14% Na2O, 10-12% CaO. Easier to form and used in
flat glass and container
경상대학교 Ceramic Design Lab.
TABLE 11.5 Compositions of Some Silicate Glasses
경상대학교 Ceramic Design Lab.
TABLE 11.6 Compositions of Some Glass-Ceramics
경상대학교 Ceramic Design Lab.
• Fusion casting
• Slip casting
• Sintering
• Hot isostatic pressing (HIP)
• Glass forming
• Controlled devitrification
• Sol-gel processing
• Biomimetic processing
• Self-propagating high temperature synthesis (SHS)
Some major processing methods for ceramics
and glasses
경상대학교 Ceramic Design Lab.
• Pressing:
GLASS
FORMING
Ceramic Fabrication Methods-I
Gob
Parison mold
Pressing operation
• Blowing:
suspended Parison
Finishing mold
Compressed air
plates, dishes, cheap glasses
--mold is steel with
graphite lining
• Fiber drawing:
wind up
PARTICULATE
FORMING
CEMENTATION
경상대학교 Ceramic Design Lab.
The high degree of flatness achieved in modern architectural plate glass is the result of the float glass process in which the layer of glass is drawn across a bath of molten tin.
Flat glass process developed by the Pilkington Glass Company
경상대학교 Ceramic Design Lab.
• Quartz is crystalline
SiO2:
• Basic Unit: • Glass is amorphous
• Amorphous structure occurs by adding impurities
(Na+,Mg2+,Ca2+, Al3+)
• Impurities: interfere with formation of
crystalline structure.
(soda glass)
Glass Structure
Si0 4 tetrahedron 4-
Si 4+
O 2 -
Si 4+
Na +
O 2 -
경상대학교 Ceramic Design Lab.
• Milling and screening: desired particle size
• Mixing particles & water: produces a "slip" • Form a "green" component
• Dry and fire the component
ram bille
t container
container force
die holder
die
A o
A d extrusion --Hydroplastic forming: extrude the slip (e.g., into a pipe)
Ceramic Fabrication Methods-IIA
solid component
--Slip casting:
hollow component
pour slip
into mold
drain
mold “green
ceramic”
pour slip into mold
absorb water into mold
“green ceramic”
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
경상대학교 Ceramic Design Lab.
•Slip casting of ceramics (“slip” = powder-water mixture)
•Much of the water absorbed into the porous mold.
경상대학교 Ceramic Design Lab.
Clay Composition
A mixture of components used
(50%) 1. Clay
(25%) 2. Filler – e.g. quartz (finely ground)
(25%) 3. Fluxing agent (Feldspar)
binds it together
aluminosilicates + K+, Na+, Ca+
경상대학교 Ceramic Design Lab.
• Clay is inexpensive
• Adding water to clay -- allows material to shear easily
along weak van der Waals bonds
-- enables extrusion
-- enables slip casting
• Structure of
Kaolinite Clay:
Features of a Slip
weak van der Waals bonding
charge neutral
charge neutral
Si 4+
Al 3 +
- OH
O 2-
Shear
Shear
경상대학교 Ceramic Design Lab.
• Drying: layer size and spacing decrease.
Drying and Firing
Drying too fast causes sample to warp or crack due to non-uniform shrinkage
wet slip partially dry “green” ceramic
• Firing: --T raised to (900-1400°C)
--vitrification: liquid glass forms from clay and flows between
SiO2 particles. Flux melts at lower T.
Si02 particle
(quartz)
glass formed around the particle
micrograph of porcelain
70 mm
경상대학교 Ceramic Design Lab.
Sintering: useful for both clay and non-clay compositions.
• Procedure: -- produce ceramic and/or glass particles by grinding
-- place particles in mold
-- press at elevated T to reduce pore size.
• Aluminum oxide powder: -- sintered at 1700°C
for 6 minutes.
Ceramic Fabrication Methods-IIB
15 mm
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
경상대학교 Ceramic Design Lab.
Powder Pressing
Sintering - powder touches - forms neck & gradually neck thickens – add processing aids to help form neck
– little or no plastic deformation Uniaxial compression - compacted in single direction
Isostatic (hydrostatic) compression - pressure applied by
fluid - powder in rubber envelope
Hot pressing - pressure + heat
경상대학교 Ceramic Design Lab.
Tape Casting
• thin sheets of green ceramic cast as flexible tape
• used for integrated circuits and capacitors
• cast from liquid slip (ceramic + organic solvent)
경상대학교 Ceramic Design Lab.
Porosity effect
2
01 1 9 0 9( . . )E E P P +
0exp( )
fnP
where P: 기공의 부피분율, E0: 기공이 없는 재료의 탄성율
where 0와 n은 실험상수
경상대학교 Ceramic Design Lab.
• Produced in extremely large quantities.
• Portland cement: -- mix clay and lime bearing materials
-- calcinate (heat to 1400°C)
-- primary constituents:
tri-calcium silicate
di-calcium silicate
• Adding water -- produces a paste which hardens
-- hardening occurs due to hydration (chemical reactions
with the water).
• Forming: done usually minutes after hydration begins.
Ceramic Fabrication Methods-III
GLASS
FORMING
PARTICULATE
FORMING
CEMENTATION
경상대학교 Ceramic Design Lab.
From Wikipedia, the free encyclopedia
“Biomimetics (also known as Bionics,
biognosis, biomimicry or bionical
creativity engineering) is the application
of biological methods and systems found
in nature to the study and design of
engineering systems and modern
technology”
"taking design ideas from nature"
“Biomimetic refers to human-made
processes, materials, devices, or systems
that imitate nature.”
Biomimetic processing
경상대학교 Ceramic Design Lab.
Advanced Materials, Functional Materials, Smart Materials, Intelligent Materials !! Conscious Materials ??!!!
Lotus effect: Self-clean water
repellent surfaces:
Structural colors:
Photonic Crystals
Bio-Adhesion:
nano-
velcro;
Geckel
glue
Low temp
ceramics
경상대학교 Ceramic Design Lab.
Gecko feet: biology
Millions of hairs
called setae
Fiber radius is
nanometer-scale
Adhesion due to
van der Waals
and capillary
forces
• Use electron beam lithography
and dry etching to create synthetic
polymer hairs
• Attach to flexible base
• Palm-sized piece can support a
human
경상대학교 Ceramic Design Lab.
drag reduction by shark skin
special alignment and grooved structure
of tooth-like scales embedded in shark skin
decrease drag and thus
greatly increase swimming proficiency
Airbus fuel consumption down 1½ %
when “shark skin” coating applied to aircraft
Friction-Reducing Sharkskin
Speedo's Fastskin FSII swimsuits made
their appearance at the Bejing Olympics
and may have helped US swimmer
Michael Phelps to his record eight gold
medals
경상대학교 Ceramic Design Lab.
Butterfly-Inspired Displays
By mimicking the way light reflects from the
scales on a butterfly's wings, the Qualcomm
company has developed Mirasol Displays
that make use of the reflected light principle
with an understanding of how human beings
perceive that light. Using an interferometric
modulator [IMOD] element in a two-plate
conductive system, the display uses near-
zero power whenever the displayed image is
static while at the same time offering a
refresh rate fast enough for video. Perfect
for 'smart' hand-held devices, already
deployed in many, and a battery-saver
extraordinaire!
경상대학교 Ceramic Design Lab.
Apatite related biomaterials
Basics of biominralization of bones
1) Osteogenic differentiation of
mesenchymal stem cells (MSCs).
2) Organization of matrix proteins
secreted from osteoblasts.
3) Nucleation and crystal growth of
apatite minerals on matrix.
Fig. Biomimetic mineralization of apatite in fibrin gel
경상대학교 Ceramic Design Lab.
Self-propagating High-temperature Synthesis (SHS)
The SHS is a method for producing inorganic compounds by exothermic
reactions, usually involving salts or pure metals. A variant of this method is
known as solid state metathesis (SSM). Since the process occurs at high
temperatures, the method is ideally suited for the production of refractory
materials with unusual properties, for example: powders, metallic alloys, or
ceramics with high purity, corrosion–resistance at high–temperature or super-
hardnessity.
FIG. Laboratory setup for combustion synthesis. 1-reaction chamber;
2-sample; 3-base; 4-quart.z window; 5-tungsten coil; &power supply;
7-video camera; &video cassette recorder; 9-video monitor; 1 O-
computer with data acquisition board; 1 I-thermocouple; 12-vacuum
pump; 13-inert or reactant gas; 14-valve.
경상대학교 Ceramic Design Lab.
Mechanical Properties
We know that ceramics are more brittle than
metals. Why?
• Consider method of deformation
– slippage along slip planes
• in ionic solids this slippage is very difficult
• too much energy needed to move one anion past
another anion
경상대학교 Ceramic Design Lab.
Figure. The frequency distribution of observed
fracture strengths for a silicon nitride material
Figure. For brittle ceramic materials, schematic
representations of crack origins and configurations.
경상대학교 Ceramic Design Lab.
Figure. Schematic diagram that shows typical
features observed on the fracture surface of a
brittle ceramic.
경상대학교 Ceramic Design Lab.
Thermal Expansion
• Materials change size when heating.
)TT(L
LLinitialfinal
initial
initialfinal a
coefficient of
thermal expansion (1/K or 1/°C)
T init
T final L final
L init
• Atomic view: Mean bond length increases with T.
Bond energy
Bond length (r)
incre
asin
g T
T 1
r(T
5)
r(T
1)
T 5 bond energy vs bond length curve is “asymmetric”
경상대학교 Ceramic Design Lab.
Thermal Expansion: Comparison
• Q: Why does a
generally decrease
with increasing
bond energy?
Polypropylene 145-180 Polyethylene 106-198
Polystyrene 90-150 Teflon 126-216
• Polymers at room T
• Ceramics Magnesia (MgO) 13.5
Alumina (Al2O3) 7.6
Soda-lime glass 9 Silica (cryst. SiO2) 0.4
• Metals Aluminum 23.6 Steel 12
Tungsten 4.5 Gold 14.2
a(10-6/K) Material
Polymers have smaller
a because of weak
secondary bonds
경상대학교 Ceramic Design Lab.
• General: The ability of a material to transfer heat.
• Quantitative: temperature
gradient
thermal conductivity (J/m-K-s)
heat flux
(J/m2-s)
• Atomic view: Atomic vibrations in hotter region carry
energy (vibrations) to cooler regions.
T 2 > T 1 T 1
x 1 x 2 heat flux
Thermal Conductivity
dx
dTkq Fourier’s Law
경상대학교 Ceramic Design Lab.
Thermal Conductivity: Comparison in
cre
asin
g k
• Polymers Polypropylene 0.12 Polyethylene 0.46-0.50 Polystyrene 0.13 Teflon 0.25
By vibration/ rotation of chain molecules
• Ceramics Magnesia (MgO) 38 Alumina (Al2O3) 39 Soda-lime glass 1.7 Silica (cryst. SiO2) 1.4
By vibration of atoms
• Metals Aluminum 247 Steel 52 Tungsten 178 Gold 315
By vibration of atoms and motion of electrons
k (W/m-K) Energy Transfer Material
경상대학교 Ceramic Design Lab.
• Occurs due to: -- uneven heating/cooling
-- mismatch in thermal expansion.
• Example -- A brass rod is stress-free at room temperature (20°C).
-- It is heated up, but prevented from lengthening.
-- At what T does the stress reach -172 MPa?
Thermal Stress
)( roomthermal
room
TTL
La
T room
L room
T
L
100GPa 20 x 10-6 /°C
20°C Answer: 106°C -172 MPa
compressive keeps L = 0
E(thermal ) Ea(T Troom)
경상대학교 Ceramic Design Lab.
• Occurs due to: uneven heating/cooling.
• Ex: Assume top thin layer is rapidly cooled from T1 to T2:
Tension develops at surface
)( 21 TTE a
Critical temperature difference
for fracture (set = f)
a
ETT f
f racture21 )(
set equal
• Large thermal shock resistance when is large. a
E
kf
• Result: a
E
kff racture f orrate) (quench
Thermal Shock Resistance
Temperature difference that
can be produced by cooling:
kTT
rate quench)( 21
rapid quench
resists contraction
tries to contract during cooling T2
T1
경상대학교 Ceramic Design Lab.
• Application:
Space Shuttle Orbiter
• Silica tiles (400-1260C): --large scale application --microstructure:
Thermal Protection System
reinf C-C (1650°C)
Re-entry T Distribution
silica tiles (400-1260°C)
nylon felt, silicon rubber coating (400°C)
~90% porosity!
Si fibers
bonded to one
another during
heat treatment. 100 mm
경상대학교 Ceramic Design Lab.
Applications: Advanced Ceramics
Heat Engines
• Advantages: – Run at higher
temperature
– Excellent wear &
corrosion resistance
– Low frictional losses
– Ability to operate without
a cooling system
– Low density
• Disadvantages:
– Brittle
– Too easy to have voids-
weaken the engine
– Difficult to machine
• Possible parts – engine block, piston coatings, jet engines
Ex: Si3N4, SiC, & ZrO2
경상대학교 Ceramic Design Lab.
Applications: Advanced Ceramics
• Ceramic Armor
– Al2O3, B4C, SiC & TiB2
– Extremely hard materials
• shatter the incoming projectile
• energy absorbent material underneath
경상대학교 Ceramic Design Lab.
Applications: Advanced Ceramics
Electronic Packaging
• Chosen to securely hold microelectronics & provide heat transfer
• Must match the thermal expansion coefficient of the microelectronic chip & the electronic packaging material. Additional requirements include:
– good heat transfer coefficient
– poor electrical conductivity
• Materials currently used include: • Boron nitride (BN)
• Silicon Carbide (SiC)
• Aluminum nitride (AlN)
– thermal conductivity 10x that for Alumina
– good expansion match with Si
경상대학교 Ceramic Design Lab.
Optical Properties
Light has both particulate and wavelike properties
– Photons - with mass
hchE
m/s) 10 x (3.00 light of speed c
)sJ1062.6( constant sPlanck'
frequency
wavelength
energy
8
34
xh
E
경상대학교 Ceramic Design Lab.
Refractive Index, n
• Note: n = f ()
Typical glasses ca. 1.5 -1.7
Plastics 1.3 -1.6
PbO (Litharge) 2.67
Diamond 2.41
medium)inlightof(velocity
vacuum)inlightof(velocity
v
c
• Transmitted light distorts electron clouds.
• Light is slower in a material vs vacuum.
n = refractive index
+ no
transmitted light
transmitted light
+
electron cloud distorts
--Adding large, heavy ions (e.g., lead
can decrease the speed of light.
--Light can be
"bent"
경상대학교 Ceramic Design Lab.
Total Internal Reflectance
sin
sin
n
nn’(low)
n (high)
n > n’
1
c
'
1
angle critical
angle refracted
angle incident
c
i
i
reflected internally is light for
90 whenoccurs
ci
ic
경상대학교 Ceramic Design Lab.
Example: Diamond in air
• Fiber optic cables are clad in low n material for this reason.
5.2441.2
1sin
sin
1
sin
90sin
1
41.2
sin
sin
cc
ccn
n
경상대학교 Ceramic Design Lab.
• Incident light is either reflected, absorbed, or
transmitted: SRATo IIIII +++
Light Interaction with Solids
• Optical classification of materials:
single
crystal
polycrystalline
dense
polycrystalline
porous
Transparent Translucent
Opaque
Incident: I0
Absorbed: IA
Transmitted: IT
Scattered: IS
Reflected: IR
경상대학교 Ceramic Design Lab.
• Absorption of photons by electron transition:
• Metals have a fine succession of energy states.
• Near-surface electrons absorb visible light.
Optical Properties of Metals:
Absorption
Energy of electron
Planck’s constant
(6.63 x 10-34 J/s)
freq. of incident light
filled states
unfilled states
E = h required!
I o
경상대학교 Ceramic Design Lab.
Light Absorption
tI
I ln
0
a
t
I
I a e0 thicknesssample
cm][tcoefficienabsorptionlinear 1
a
t
경상대학교 Ceramic Design Lab.
• Reflectivity = IR/Io is between 0.90 and 0.95.
• Reflected light is same frequency as incident.
• Metals appear reflective (shiny)!
Optical Properties of Metals:
Reflection
• Electron transition emits a photon.
re-emitted
photon from
material surface
Energy of electron
filled states
unfilled states
E
IR “conducting” electron
경상대학교 Ceramic Design Lab.
Reflectivity, R
• Reflection
– Metals reflect almost all light
– Copper & gold absorb in blue & green => gold
color
tyreflectivi1
12
+
n
nR
17.0141.2
141.22
+
R
reflectedislightof%17
• Example: Diamond
경상대학교 Ceramic Design Lab.
Scattering
• In semicrystalline or polycrystalline
materials
• Semicrystalline – density of crystals higher than amorphous
materials speed of light is lower - causes light to
scatter - can cause significant loss of light
• Common in polymers
– Ex: LDPE milk cartons – cloudy
– Polystyrene – clear – essentially no crystals
경상대학교 Ceramic Design Lab.
• Absorption by electron transition occurs if h > Egap
• If Egap < 1.8 eV, full absorption; color is black (Si, GaAs)
• If Egap > 3.1 eV, no absorption; colorless (diamond)
• If Egap in between, partial absorption; material has a color.
Selected Absorption: Semiconductors
incident photon
energy h
Energy of electron
filled states
unfilled states
E gap
I o
blue light: h = 3.1 eV
red light: h = 1.7 eV
경상대학교 Ceramic Design Lab.
c hc
Eg
(6.62 x 1034 J s)(3 x 108m/s)
(0.67eV)(1.60 x 1019 J/eV) 1.85 mm
note : for Si Eg 1.1eV c 1.13 mm
Wavelength vs. Band Gap
If donor (or acceptor) states also available this provides other
absorption frequencies
Eg = 0.67 eV
Example: What is the minimum wavelength absorbed
by Ge?
경상대학교 Ceramic Design Lab.
• Color determined by sum of frequencies of -- transmitted light,
-- re-emitted light from electron transitions.
• Ex: Cadmium Sulfide (CdS) -- Egap = 2.4 eV,
-- absorbs higher energy visible light (blue, violet),
-- Red/yellow/orange is transmitted and gives it color.
Color of Nonmetals
• Ex: Ruby = Sapphire (Al2O3) + (0.5 to 2) at% Cr2O3 -- Sapphire is colorless (i.e., Egap > 3.1eV)
-- adding Cr2O3 : • alters the band gap
• blue light is absorbed
• yellow/green is absorbed
• red is transmitted
• Result: Ruby is deep red in color.
40
60
70
80
50
0.3 0.5 0.7 0.9
Tra
nsm
itta
nce (
%)
ruby
sapphire
wavelength, (= c/)(mm)
경상대학교 Ceramic Design Lab.
Luminescence • Luminescence – emission of light by a
material
– material absorbs light at one frequency & emits at
another (lower) frequency.
activator level
Valence band
Conduction band
trapped states Eg
Eemission
How stable is the trapped state?
• If very stable (long-lived = >10-8 s) = phosphorescence
• If less stable (<10-8 s) = fluorescence
Example: glow in the dark toys. Charge them up by exposing them to the light. Reemit over time. -- phosphorescence
경상대학교 Ceramic Design Lab.
Photoluminescence
• Arc between electrodes excites mercury in lamp to higher
energy level.
• electron falls back emitting UV light (i.e., suntan lamp).
• Line inner surface with material that absorbs UV, emits visible
Ca10F2P6O24 with 20% of F - replaced by Cl
-
• Adjust color by doping with metal cations
Sb3+ blue
Mn2+ orange-red
Hg
uv
electrode electrode
경상대학교 Ceramic Design Lab.
Cathodoluminescence
• Used in T.V. set
– Bombard phosphor with electrons
– Excite phosphor to high state
– Relaxed by emitting photon (visible) ZnS (Ag+ & Cl-) blue
(Zn, Cd) S + (Cu++Al3+) green
Y2O2S + 3% Eu red
• Note: light emitted is random in phase & direction
– i.e., noncoherent
경상대학교 Ceramic Design Lab.
LASER Light
• Is non-coherent light a problem? – diverges – can’t keep tightly columnated
• How could we get all the light in phase? (coherent)
– LASERS • Light
• Amplification by
• Stimulated
• Emission of
• Radiation
• Involves a process called population inversion of energy states
경상대학교 Ceramic Design Lab.
Population Inversion
• What if we could increase most species to the excited
state?
경상대학교 Ceramic Design Lab.
LASER Light Production
• “pump” the lasing material to the excited state
– e.g., by flash lamp (non-coherent lamp).
– If we let this just decay we get no coherence.
경상대학교 Ceramic Design Lab.
LASER Cavity
“Tuned” cavity:
• Stimulated Emission – One photon induces the
emission of another
photon, in phase with the
first.
– cascades producing very
intense burst of coherent
radiation.
• i.e., Pulsed laser
경상대학교 Ceramic Design Lab.
Continuous Wave LASER
• Can also use materials such as CO2 or yttrium- aluminum-garret (YAG) for LASERS
• Set up standing wave in laser cavity –
– tune frequency by adjusting mirror spacing.
• Uses of CW lasers 1. Welding
2. Drilling
3. Cutting – laser carved wood, eye surgery
4. Surface treatment
5. Scribing – ceramics, etc.
6. Photolithography – Excimer laser
경상대학교 Ceramic Design Lab.
• Apply strong forward
bias to junction.
Creates excited state
by pumping electrons
across the gap-
creating electron-hole
pairs.
electron + hole neutral + h
excited state ground state photon of
light
Semiconductor LASER
경상대학교 Ceramic Design Lab.
Uses of Semiconductor LASERs
• #1 use = compact disk player
– Color? - red
• Banks of these semiconductor lasers are used as
flash lamps to pump other lasers
• Communications
– Fibers often turned to a specific frequency
(typically in the blue)
– only recently was this a attainable
경상대학교 Ceramic Design Lab.
Applications of Materials Science
• New materials must be developed to make new &
improved optical devices.
– Organic Light Emitting Diodes (OLEDs)
– White light semiconductor sources
• New semiconductors
• Materials scientists
(& many others) use lasers as tools.
• Solar cells
경상대학교 Ceramic Design Lab.
Solar Cells
• p-n junction: • Operation: -- incident photon produces hole-elec. pair.
-- typically 0.5 V potential.
-- current increases w/light intensity.
• Solar powered weather station:
polycrystalline Si
n-type Si
P-type Si p-n junction
B-doped Si
Si
Si
Si Si B
hole
P
Si
Si
Si Si
conductance electron
P-doped Si
n-type Si
p-type Si p-n junction
light
+ -
+ + +
- - -
creation of
hole-electron
pair
경상대학교 Ceramic Design Lab.
Optical Fibers
• prepare preform as indicated in Chapter 13
• preform drawn to 125 mm or less capillary fibers
• plastic cladding applied 60 mm
경상대학교 Ceramic Design Lab.
Optical Fiber Profiles
Step-index Optical Fiber
Graded-index Optical Fiber
경상대학교 Ceramic Design Lab.
• Steels: increase TS, Hardness (and cost) by adding
--C (low alloy steels)
--Cr, V, Ni, Mo, W (high alloy steels)
--ductility usually decreases w/additions.
• Non-ferrous:
--Cu, Al, Ti, Mg, Refractory, and noble metals.
• Fabrication techniques:
--forming, casting, joining.
Ceramic materials have covalent & ionic bonding.
• Structures are based on:
-- charge neutrality
-- maximizing # of nearest oppositely charged neighbors.
• Structures may be predicted based on:
-- ratio of the cation and anion radii.
Summary
경상대학교 Ceramic Design Lab.
• Defects
-- must preserve charge neutrality
-- have a concentration that varies exponentially w/T.
• Room T mechanical response is elastic, but fracture
is brittle, with negligible deformation.
• Elevated T creep properties are generally superior to
those of metals (and polymers).
• Fabrication Techniques: -- glass forming (impurities affect forming temp).
-- particulate forming (needed if ductility is limited)
-- cementation (large volume, room T process)
• Heat treating: Used to -- alleviate residual stress from cooling,
-- produce fracture resistant components by putting
surface into compression.