Chapter 11: Applications and Processing of Metal Alloys

Chapter 11 - 1

Chapter 11: Applications and Processing of Metal Alloys

ISSUES TO ADDRESS...• How are metal alloys classified and what are their

common applications?• What are some of the common fabrication techniques

for metals?• What heat treatment procedures are used to improve the

mechanical properties of both ferrous and nonferrous alloys?

Chapter 11 - 2

Adapted from Fig. 9.24, Callister & Rethwisch 8e. (Fig. 9.24 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)

Adapted from Fig. 11.1, Callister & Rethwisch 8e.

Classification of Metal AlloysMetal Alloys

Steels

Ferrous Nonferrous

Cast Irons<1.4wt%C 3-4.5wt%CSteels

<1.4wt%CCast Irons3-4.5wt%C

Fe3C cementite

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

γaustenite

γ+L

γ+Fe3Cα

ferriteα+Fe3C

L+Fe3C

δ

(Fe) Co , wt% C

Eutectic:

Eutectoid:0.76

4.30

727ºC

1148ºC

T(ºC) microstructure: ferrite,graphite/cementite

Chapter 11 - 3Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister & Rethwisch 8e.

SteelsLow Alloy High Alloy

low carbon <0.25wt%C

Med carbon0.25-0.6wt%C

high carbon 0.6-1.4wt%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

Very corros. resistant

Example 1010 4310 1040 4340 1095 4190 304, 409

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 stainlessName

Hardenability 0 + + ++ ++ +++ variesTS - 0 + ++ + ++ variesEL + + 0 - - -- ++

increasing strength, cost, decreasing ductility

Chapter 11 - 4

Refinement of Steel from Ore

Iron OreCoke

Limestone

3CO+Fe2O3 →2Fe+3CO2

C+O2 →CO2

CO2 +C→ 2CO

CaCO3 → CaO+CO2CaO + SiO2 + Al2O3 → slag

purification

reduction of iron ore to metal

heat generation

Molten iron

BLAST FURNACE

slagair

layers of cokeand iron ore

gasrefractory vessel

Chapter 11 - 5

Ferrous AlloysIron-based alloys

Nomenclature for steels (AISI/SAE)10xx Plain Carbon Steels11xx Plain Carbon Steels (resulfurized for machinability) 15xx Mn (1.00 - 1.65%)40xx Mo (0.20 ~ 0.30%)43xx Ni (1.65 - 2.00%), Cr (0.40 - 0.90%), Mo (0.20 - 0.30%)44xx Mo (0.5%)

where xx is wt% C x 100example: 1060 steel – plain carbon steel with 0.60 wt% C

Stainless Steel >11% Cr

• Steels• Cast Irons

Chapter 11 - 6

Cast Irons• Ferrous alloys with > 2.1 wt% C

– more commonly 3 - 4.5 wt% C• Low melting – relatively easy to cast• Generally brittle

• Cementite decomposes to ferrite + graphiteFe3C 3 Fe (α) + C (graphite)

– generally a slow process

Chapter 11 - 7

Fe-C True Equilibrium Diagram

Graphite formation promoted by

• Si > 1 wt%

• slow cooling

Adapted from Fig. 11.2, Callister & Rethwisch 8e.[Fig. 11.2 adapted from Binary Alloy Phase Diagrams, 2nd ed.,Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.]

1600

1400

1200

1000

800

600

4000 1 2 3 4 90

L

γ +L

α + Graphite

Liquid +Graphite

(Fe) C, wt% C

0.65

740ºC

T(ºC)

γ + Graphite

100

1153ºCγAustenite 4.2 wt% C

α + γ

Chapter 11 - 8

Types of Cast IronGray iron• graphite flakes• weak & brittle in tension• stronger in compression• excellent vibrational dampening• wear resistant

Ductile iron• add Mg and/or Ce• graphite as nodules not flakes• matrix often pearlite – stronger

but less ductile

Adapted from Fig. 11.3(a) & (b), Callister & Rethwisch 8e.

Chapter 11 - 9

Types of Cast Iron (cont.)White iron• < 1 wt% Si• pearlite + cementite• very hard and brittle

Malleable iron• heat treat white iron at 800-900ºC• graphite in rosettes• reasonably strong and ductile

Adapted from Fig. 11.3(c) & (d), Callister & Rethwisch 8e.

Chapter 11 - 10

Types of Cast Iron (cont.)Compacted graphite iron• relatively high thermal conductivity• good resistance to thermal shock• lower oxidation at elevated

temperatures

Adapted from Fig. 11.3(e), Callister & Rethwisch 8e.

Chapter 11 - 11

Production of Cast Irons

Adapted from Fig.11.5, Callister & Rethwisch 8e.

Chapter 11 - 12

Limitations of Ferrous Alloys

1) Relatively high densities2) Relatively low electrical conductivities3) Generally poor corrosion resistance

Chapter 11 - 13Based on discussion and data provided in Section 11.3, Callister & Rethwisch 3e.

Nonferrous Alloys

NonFerrous Alloys

• Al Alloys-low ρ: 2.7 g/cm3

-Cu, Mg, Si, Mn, Zn additions -solid sol. or precip.

strengthened (struct. aircraft parts & packaging)

• Mg Alloys-very low ρ: 1.7g/cm3

-ignites easily -aircraft, missiles

• Refractory metals-high melting T’s-Nb, Mo, W, Ta• Noble metals

-Ag, Au, Pt -oxid./corr. resistant

• Ti Alloys-relatively low ρ: 4.5 g/cm3

vs 7.9 for steel-reactive at high T’s-space applic.

• Cu AlloysBrass: Zn is subst. impurity(costume jewelry, coins, corrosion resistant)Bronze : Sn, Al, Si, Ni are subst. impurities (bushings, landing gear)Cu-Be: precip. hardened for strength

Chapter 11 - 14

Metal Fabrication• How do we fabricate metals?

– Blacksmith - hammer (forged)– Cast molten metal into mold

• Forming Operations – Rough stock formed to final shape

Hot working vs. Cold working• Deformation temperature

high enough for recrystallization

• Large deformations

• Deformation belowrecrystallization temperature

• Strain hardening occurs• Small deformations

Chapter 11 - 15

FORMING

roll

AoAd

roll

• Rolling (Hot or Cold Rolling)(I-beams, rails, sheet & plate)

Ao Ad

force

dieblank

force

• Forging (Hammering; Stamping)(wrenches, crankshafts)

often atelev. T


Metal Fabrication Methods (i)

ram billet

container

containerforce die holder

die

Ao

Adextrusion

• Extrusion(rods, tubing)

ductile metals, e.g. Cu, Al (hot)

tensile force

AoAddie

die

• Drawing(rods, wire, tubing)

die must be well lubricated & clean

CASTING MISCELLANEOUS

Chapter 11 - 16

FORMING CASTING

Metal Fabrication Methods (ii)

• Casting- mold is filled with molten metal– metal melted in furnace, perhaps alloying

elements added, then cast in a mold – common and inexpensive– gives good production of shapes– weaker products, internal defects– good option for brittle materials

MISCELLANEOUS

Chapter 11 - 17

• Sand Casting(large parts, e.g.,auto engine blocks)

Metal Fabrication Methods (iii)

• What material will withstand T >1600ºCand is inexpensive and easy to mold?

• Answer: sand!!!

• To create mold, pack sand around form (pattern) of desired shape

Sand Sand

molten metal

FORMING CASTING MISCELLANEOUS

Chapter 11 - 18

• Stage I — Mold formed by pouring plaster of paris around wax pattern. Plaster allowed to harden.

• Stage II — Wax is melted and then poured from mold—hollow mold cavity remains.

• Stage III — Molten metal is poured into mold and allowed to solidify.

Metal Fabrication Methods (iv)

FORMING CASTING MISCELLANEOUS• Investment Casting

(low volume, complex shapese.g., jewelry, turbine blades)

wax I

II

III

Chapter 11 - 19

Metal Fabrication Methods (v)

• Continuous Casting-- simple shapes

(e.g., rectangular slabs, cylinders)

molten

solidified

FORMING CASTING MISCELLANEOUS

• Die Casting-- high volume-- for alloys having low melting

temperatures

Chapter 11 - 20

MISCELLANEOUSCASTING

Metal Fabrication Methods (vi)

• Powder Metallurgy(metals w/low ductilities)

pressure

heat

point contact at low T

densificationby diffusion at higher T

area contact

densify

• Welding(when fabrication of one large part is impractical)

• Heat-affected zone:(region in which themicrostructure has beenchanged).

Adapted from Fig. 11.9, Callister & Rethwisch 8e.(Fig. 11.9 from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.)

piece 1 piece 2

fused base metal

filler metal (melted)base metal (melted)

unaffectedunaffectedheat-affected zone

FORMING

Chapter 11 - 21

Annealing: Heat to Tanneal, then cool slowly.

Based on discussion in Section 11.7, Callister & Rethwisch 8e.

Thermal Processing of Metals

Types of Annealing

• Process Anneal:Negate effects of cold working by (recovery/

recrystallization)

• Stress Relief: Reducestresses resulting from:

- plastic deformation - nonuniform cooling - phase transform.

• Normalize (steels): Deformsteel with large grains. Then heattreat to allow recrystallization and formation of smaller grains.

• Full Anneal (steels): Make soft steels for good forming. Heat to get γ, then furnace-coolto obtain coarse pearlite.

• Spheroidize (steels): Make very soft steels for good machining. Heat just

below Teutectoid & hold for15-25 h.

Chapter 11 - 22

a) Full Annealingb) Quenching

Heat Treatment Temperature-Time Paths

c)

c) Tempering (Tempered Martensite)

P

B

A

A

a)b)

Fig. 10.25,Callister & Rethwisch 8e.

Chapter 11 - 23

Hardenability -- Steels• Hardenability – measure of the ability to form martensite• Jominy end quench test used to measure hardenability.

• Plot hardness versus distance from the quenched end.

Adapted from Fig. 11.11, Callister & Rethwisch 8e. (Fig. 11.11 adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.)


24ºC water

specimen (heated to γphase field)

flat ground

Rockwell Chardness tests

Har

dnes

s, H

RC

Distance from quenched end

Chapter 11 - 24

• The cooling rate decreases with distance from quenched end.

Adapted from Fig. 11.13, Callister & Rethwisch 8e. (Fig. 11.13 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.)

Reason Why Hardness Changes with Distance

distance from quenched end (in)Har

dnes

s, H

RC

20

40

60

0 1 2 3

600

400

200A → M

0.1 1 10 100 1000

T(ºC)

M(start)

Time (s)

0

0%100%

M(finish)

Chapter 11 - 25

Hardenability vs Alloy Composition• Hardenability curves for

five alloys each with, C = 0.4 wt% C

• "Alloy Steels"(4140, 4340, 5140, 8640)-- contain Ni, Cr, Mo

(0.2 to 2 wt%)-- these elements shift

the "nose" to longer times (from A to B)

-- martensite is easierto form

Adapted from Fig. 11.14, Callister & Rethwisch 8e. (Fig. 11.14 adapted from figure furnished courtesy Republic Steel Corporation.)

Cooling rate (ºC/s)

Har

dnes

s, H

RC

20

40

60

100 20 30 40 50Distance from quenched end (mm)

210100 3

41408640

5140

50

80

100

%M4340

T(ºC)

10-1 10 103 1050

200

400

600

800

Time (s)

M(start)M(90%)

BA

TE

Chapter 11 - 26

• Effect of quenching medium:Medium

airoil

water

Severity of Quenchlow

moderatehigh

Hardnesslow

moderatehigh

• Effect of specimen geometry:When surface area-to-volume ratio increases:

-- cooling rate throughout interior increases-- hardness throughout interior increases

Positioncentersurface

Cooling ratelowhigh

Hardnesslowhigh

Influences of Quenching Medium & Specimen Geometry

Chapter 11 - 27

0 10 20 30 40 50wt% Cu

Lα+Lα

α+θθ

θ+L

300

400

500

600

700

(Al)

T(ºC)

composition range available for precipitation hardening

CuAl2

A

Adapted from Fig. 11.24, Callister & Rethwisch 8e. (Fig. 11.24 adapted from J.L. Murray, International Metals Review 30, p.5, 1985.)

Precipitation Hardening• Particles impede dislocation motion.• Ex: Al-Cu system• Procedure:


-- Pt B: quench to room temp.(retain α solid solution)

-- Pt C: reheat to nucleatesmall θ particles withinα phase.

• Other alloys that precipitationharden:• Cu-Be• Cu-Sn• Mg-Al

Temp.

Time

-- Pt A: solution heat treat(get α solid solution)

Pt A (sol’n heat treat)

B

Pt B

C

Pt C (precipitate θ)

Chapter 11 - 28

• 2014 Al Alloy:

• Maxima on TS curves.• Increasing T accelerates

process.

Adapted from Fig. 11.27, Callister & Rethwisch 8e. (Fig. 11.27 adapted from Metals Handbook: Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th ed., H. Baker (Managing Ed.), American Society for Metals, 1979. p. 41.)

Influence of Precipitation Heat Treatment on TS, %EL

precipitation heat treat time

tens

ile s

treng

th (M

Pa)

200

300

400

100 1min 1h 1day 1mo 1yr

204ºC149ºC

• Minima on %EL curves.

%E

L(2

in s

ampl

e)10

20

30

0 1min 1h 1day 1mo 1yr

204ºC 149ºC

precipitation heat treat time

Chapter 11 - 29

• Ferrous alloys: steels and cast irons• Non-ferrous alloys:

-- Cu, Al, Ti, and Mg alloys; refractory alloys; and noble metals.• Metal fabrication techniques:

-- forming, casting, miscellaneous.• Hardenability of metals

-- measure of ability of a steel to be heat treated.-- increases with alloy content.

• Precipitation hardening--hardening, strengthening due to formation of

precipitate particles.--Al, Mg alloys precipitation hardenable.

Summary

Chapter 12 - 1

Chapter 12: Structures & Properties of Ceramics

ISSUES TO ADDRESS...• How do the crystal structures of ceramic materials

differ from those for metals?• How do point defects in ceramics differ from those

defects found in metals?• How are impurities accommodated in the ceramic lattice?

• How are the mechanical properties of ceramics measured, and how do they differ from those for metals?

• In what ways are ceramic phase diagrams different from phase diagrams for metals?

Chapter 12 - 2

• Bonding:-- Can be ionic and/or covalent in character.-- % ionic character increases with difference in

electronegativity of atoms.

Adapted from Fig. 2.7, Callister & Rethwisch 8e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 byCornell University.)

• Degree of ionic character may be large or small:

Atomic Bonding in Ceramics

SiC: smallCaF2: large

Chapter 12 - 3

Ceramic Crystal Structures

Oxide structures– oxygen anions larger than metal cations– close packed oxygen in a lattice (usually FCC)– cations fit into interstitial sites among oxygen ions

Chapter 12 - 4

Factors that Determine Crystal Structure1. Relative sizes of ions – Formation of stable structures:

--maximize the # of oppositely charged ion neighbors.


- -

- -+

unstable

- -

- -+

stable

- -

- -+

stable2. Maintenance of

Charge Neutrality :--Net charge in ceramic

should be zero.--Reflected in chemical

formula:

CaF2: Ca2+cation

F-

F-

anions+

AmXpm, p values to achieve charge neutrality

Chapter 12 - 5

• Coordination # increases with

Coordination # and Ionic Radii

Adapted from Table 12.2, Callister & Rethwisch 8e.

2

rcationranion

Coord #

< 0.155

0.155 - 0.225

0.225 - 0.414

0.414 - 0.732

0.732 - 1.0

3

4

6

8

linear

triangular

tetrahedral

octahedral

cubic




ZnS (zinc blende)

NaCl(sodium chloride)

CsCl(cesium chloride)

rcationranion

To form a stable structure, how many anions cansurround around a cation?

Chapter 12 - 6

Computation of Minimum Cation-Anion Radius Ratio

• Determine minimum rcation/ranion for an octahedral site (C.N. = 6)

a = 2ranion

2ranion + 2rcation = 2 2ranion

ranion + rcation = 2ranion

rcation = ( 2 −1)ranion

arr 222 cationanion =+

414.012anion

cation =−=rr

Chapter 12 - 7

Bond HybridizationBond Hybridization is possible when there is significant

covalent bonding– hybrid electron orbitals form– For example for SiC

• XSi = 1.8 and XC = 2.5

% ionic character = 100 {1- exp[-0.25(XSi − XC)2]} = 11.5%

• ~ 89% covalent bonding• Both Si and C prefer sp3 hybridization• Therefore, for SiC, Si atoms occupy tetrahedral sites

Chapter 12 - 8

• On the basis of ionic radii, what crystal structurewould you predict for FeO?

• Answer:

550014000770

anion

cation

...

rr

=

=

based on this ratio,-- coord # = 6 because

0.414 < 0.550 < 0.732

-- crystal structure is NaClData from Table 12.3, Callister & Rethwisch 8e.

Example Problem: Predicting the Crystal Structure of FeO

Ionic radius (nm)0.0530.0770.0690.100

0.1400.1810.133

Cation

Anion

Al3+

Fe2+

Fe3+

Ca2+

O2-

Cl-

F-

Chapter 12 - 9

Rock Salt StructureSame concepts can be applied to ionic solids in general. Example: NaCl (rock salt) structure

rNa = 0.102 nm

rNa/rCl = 0.564

∴ cations (Na+) prefer octahedral sites


rCl = 0.181 nm

Chapter 12 - 10

MgO and FeO

O2- rO = 0.140 nm

Mg2+ rMg = 0.072 nm

rMg/rO = 0.514

∴ cations prefer octahedral sites

So each Mg2+ (or Fe2+) has 6 neighbor oxygen atoms


MgO and FeO also have the NaCl structure

Chapter 12 - 11

AX Crystal Structures

939.0181.0170.0

Cl

Cs ==−

+

r

r


Cesium Chloride structure:

∴ Since 0.732 < 0.939 < 1.0, cubic sites preferred

So each Cs+ has 8 neighbor Cl-

AX–Type Crystal Structures include NaCl, CsCl, and zinc blende

Chapter 12 - 12

AX2 Crystal Structures

• Calcium Fluorite (CaF2)• Cations in cubic sites

• UO2, ThO2, ZrO2, CeO2

• Antifluorite structure –positions of cations and anions reversed


Fluorite structure

Chapter 12 - 13

ABX3 Crystal Structures


• Perovskite structure

Ex: complex oxide BaTiO3

Chapter 12 -

VMSE: Ceramic Crystal Structures

14

Chapter 12 - 15

Density Computations for Ceramics

A

AC )(NV

AAn

C

Σ+Σ′=ρ

Number of formula units/unit cell

Volume of unit cell

Avogadro’s number

= sum of atomic weights of all anions in formula unit

ΣAA

ΣAC = sum of atomic weights of all cations in formula unit

Chapter 12 - 16

Silicate CeramicsMost common elements on earth are Si & O

• SiO2 (silica) polymorphic forms are quartz, crystobalite, & tridymite

• The strong Si-O bonds lead to a high melting temperature (1710ºC) for this material

Si4+

O2-

Adapted from Figs. 12.9-10, Callister & Rethwisch 8e crystobalite

Chapter 12 - 17

Bonding of adjacent SiO44- accomplished by the

sharing of common corners, edges, or faces

Silicates

Mg2SiO4 Ca2MgSi2O7


Presence of cations such as Ca2+, Mg2+, & Al3+

1. maintain charge neutrality, and2. ionically bond SiO4

4- to one another

Chapter 12 - 18

• Quartz is crystallineSiO2:

• Basic Unit: Glass is noncrystalline (amorphous)• Fused silica is SiO2 to which no

impurities have been added• Other common glasses contain

impurity ions such as Na+, Ca2+, Al3+, and B3+

(soda glass)Adapted from Fig. 12.11, Callister & Rethwisch 8e.

Glass Structure

Si04 tetrahedron4-

Si4+

O2-

Si4+Na+

O2-

Chapter 12 - 19

Layered Silicates• Layered silicates (e.g., clays, mica, talc)

– SiO4 tetrahedra connected together to form 2-D plane

• A net negative charge is associated with each (Si2O5)2- unit

• Negative charge balanced by adjacent plane rich in positively charged cations


Chapter 12 - 20

• Kaolinite clay alternates (Si2O5)2- layer with Al2(OH)42+

layer

Layered Silicates (cont.)

Note: Adjacent sheets of this type are loosely bound to one another by van der Waal’s forces.


Chapter 12 - 21

Polymorphic Forms of CarbonDiamond– tetrahedral bonding of

carbon• hardest material known• very high thermal

conductivity– large single crystals –

gem stones– small crystals – used to

grind/cut other materials – diamond thin films

• hard surface coatings –used for cutting tools, medical devices, etc.


Chapter 12 - 22

Polymorphic Forms of Carbon (cont)Graphite– layered structure – parallel hexagonal arrays of

carbon atoms

– weak van der Waal’s forces between layers– planes slide easily over one another -- good

lubricant


Chapter 12 - 23

Polymorphic Forms of Carbon (cont)Fullerenes and Nanotubes

• Fullerenes – spherical cluster of 60 carbon atoms, C60

– Like a soccer ball • Carbon nanotubes – sheet of graphite rolled into a tube

– Ends capped with fullerene hemispheres

Adapted from Figs. 12.18 & 12.19, Callister & Rethwisch 8e.

Chapter 12 - 24

• Vacancies-- vacancies exist in ceramics for both cations and anions

• Interstitials-- interstitials exist for cations-- interstitials are not normally observed for anions because anions

are large relative to the interstitial sites

Adapted from Fig. 12.20, Callister & Rethwisch 8e. (Fig. 12.20 is from W.G. Moffatt, G.W. Pearsall, and J. Wulff, The Structure and Properties of Materials, Vol. 1, Structure, John Wiley and Sons, Inc., p. 78.)

Point Defects in Ceramics (i)

Cation Interstitial

Cation Vacancy

Anion Vacancy

Chapter 12 - 25

• Frenkel Defect-- a cation vacancy-cation interstitial pair.

• Shottky Defect-- a paired set of cation and anion vacancies.

• Equilibrium concentration of defects

Adapted from Fig.12.21, Callister & Rethwisch 8e. (Fig. 12.21 is from W.G. Moffatt, G.W. Pearsall, and J. Wulff, The Structure and Properties of Materials, Vol. 1, Structure, John Wiley and Sons, Inc., p. 78.)

Point Defects in Ceramics (ii)

Shottky Defect:

Frenkel Defect

/kTQDe−∝

Chapter 12 - 26

• Electroneutrality (charge balance) must be maintained when impurities are present

• Ex: NaCl

Imperfections in Ceramics

Na+ Cl-• Substitutional cation impurity

without impurity Ca2+ impurity with impurity

Ca2+

Na+

Na+Ca2+

cation vacancy

• Substitutional anion impurity

without impurity O2- impurity

O2-

Cl-

anion vacancy

Cl-

with impurity

Chapter 12 - 27

Ceramic Phase DiagramsMgO-Al2O3 diagram:


°

Chapter 12 - 28

Mechanical PropertiesCeramic materials are more brittle than metals.

Why is this so?• Consider mechanism of deformation

– In crystalline, by dislocation motion– In highly ionic solids, dislocation motion is difficult

• few slip systems• resistance to motion of ions of like charge (e.g., anions)

past one another

Chapter 12 - 29

• Room T behavior is usually elastic, with brittle failure.• 3-Point Bend Testing often used.

-- tensile tests are difficult for brittle materials.


Flexural Tests – Measurement of Elastic Modulus

FL/2 L/2

δ = midpoint deflection

cross section

R

b

d

rect. circ.

• Determine elastic modulus according to:F

x

linear-elastic behaviorδ

Fδ

slope =3

3

4bdLFE

δ= (rect. cross section)

4

3

12 RLFEπδ

= (circ. cross section)

Chapter 12 - 30

• 3-point bend test to measure room-T flexural strength.


Flexural Tests – Measurement of Flexural Strength

FL/2 L/2

δ = midpoint deflection

cross section

R

b

d

rect. circ.

location of max tension

• Flexural strength: • Typical values:

Data from Table 12.5, Callister & Rethwisch 8e.

Si nitrideSi carbideAl oxideglass (soda-lime)

250-1000100-820275-700

69

30434539369

Material σfs (MPa) E(GPa)

223bd

LFffs =σ (rect. cross section)

(circ. cross section)3RLFf

fsπ

=σ

Chapter 12 - 31

SUMMARY• Interatomic bonding in ceramics is ionic and/or covalent.• Ceramic crystal structures are based on:

-- maintaining charge neutrality-- cation-anion radii ratios.

• Imperfections-- Atomic point: vacancy, interstitial (cation), Frenkel, Schottky-- Impurities: substitutional, interstitial-- Maintenance of charge neutrality

• Room-temperature mechanical behavior – flexural tests-- linear-elastic; measurement of elastic modulus-- brittle fracture; measurement of flexural modulus

Chapter 13 - 1

Chapter 13: Applications and Processing of Ceramics

ISSUES TO ADDRESS...• How do we classify ceramics?

• What are some applications of ceramics?

• How is processing of ceramics different than for metals?

Chapter 13 - 2

Glasses Clay products

Refractories Abrasives Cements Advanced ceramics

-optical -composite reinforce

-containers/ household

-whiteware -structural

-bricks for high T (furnaces)

-sandpaper -cutting -polishing

-composites -structural

-engine rotors valves bearings

-sensorsAdapted from Fig. 13.1 and discussion in Section 13.2-8, Callister & Rethwisch 8e.

Classification of Ceramics

Ceramic Materials

Chapter 13 - 3

tensile force

AoAddie

die

• Die blanks:-- Need wear resistant properties!

• Die surface:-- 4 µm polycrystalline diamond

particles that are sintered onto acemented tungsten carbidesubstrate.

-- polycrystalline diamond gives uniform hardness in all directions to reduce wear.

Adapted from Fig. 11.8(d), Callister & Rethwisch 8e.

Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.

Ceramics Application: Die Blanks

Chapter 13 - 4

• Tools:-- for grinding glass, tungsten,

carbide, ceramics-- for cutting Si wafers-- for oil drilling

bladesoil drill bits

Single crystal diamonds

polycrystallinediamonds in a resinmatrix.

Photos courtesy Martin Deakins,GE Superabrasives, Worthington,OH. Used with permission.

Ceramics Application: Cutting Tools

• Materials:-- manufactured single crystal

or polycrystalline diamondsin a metal or resin matrix.

-- polycrystalline diamondsresharpen by microfracturingalong cleavage planes.

Chapter 13 - 5

• Example: ZrO2 as an oxygen sensor• Principle: Increase diffusion rate of oxygen

to produce rapid response of sensor signal to change in oxygen concentration

Ceramics Application: Sensors

A substituting Ca2+ ion removes a Zr4+ ion and

an O2- ion.

Ca2+

• Approach:Add Ca impurity to ZrO2:-- increases O2- vacancies-- increases O2- diffusion rate

reference gas at fixed oxygen contentO2-

diffusion

gas with an unknown, higher oxygen content

-+voltage difference produced!

sensor• Operation:

-- voltage difference produced when O2- ions diffuse from the external surface through the sensor to the reference gas surface.

-- magnitude of voltage difference ∝ partial pressure of oxygen at the external surface

Chapter 13 - 6

• Materials to be used at high temperatures (e.g., in high temperature furnaces).

• Consider the Silica (SiO2) - Alumina (Al2O3) system.• Silica refractories - silica rich - small additions of alumina

depress melting temperature (phase diagram):

Fig. 12.27, Callister & Rethwisch 8e. (Fig. 12.27 adapted from F.J. Klug and R.H. Doremus, J. Am. Cer. Soc. 70(10), p. 758, 1987.)

Refractories

Composition (wt% alumina)

T(ºC)

1400

1600

1800

2000

2200

20 40 60 80 1000

alumina+

mullite

mullite + L

mulliteLiquid

(L)

mullite+ crystobalite

crystobalite + L

alumina + L

3Al2O3-2SiO2

Chapter 13 - 7

Advanced Ceramics: Materials for Automobile Engines

• Advantages: – Operate at high

temperatures – high efficiencies

– Low frictional losses– Operate without a cooling

system– Lower weights than

current engines

• Disadvantages: – Ceramic materials are

brittle– Difficult to remove internal

voids (that weaken structures)

– Ceramic parts are difficult to form and machine

• Potential candidate materials: Si3N4, SiC, & ZrO2

• Possible engine parts: engine block & piston coatings

Chapter 13 - 8

Advanced Ceramics: Materials for Ceramic Armor

Components:-- Outer facing plates-- Backing sheet

Properties/Materials:-- Facing plates -- hard and brittle

— fracture high-velocity projectile— Al2O3, B4C, SiC, TiB2

-- Backing sheets -- soft and ductile— deform and absorb remaining energy— aluminum, synthetic fiber laminates

Chapter 13 - 9

• Blowing of Glass Bottles:

GLASSFORMING

Adapted from Fig. 13.8, Callister & Rethwisch 8e. (Fig. 13.8 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)

Ceramic Fabrication Methods (i)

Gob

Parison mold

Pressing operation

Suspended parison

Finishing mold

Compressed air

• Fiber drawing:

wind up

PARTICULATEFORMING

CEMENTATION

-- glass formed by application of pressure

-- mold is steel with graphite lining

• Pressing: plates, cheap glasses

Chapter 13 -10

Sheet Glass Forming• Sheet forming – continuous casting

– sheets are formed by floating the molten glass on a pool of molten tin


Chapter 13 - 11

• Quartz is crystallineSiO2:

• Basic Unit: Glass is noncrystalline (amorphous)• Fused silica is SiO2 to which no

impurities have been added• Other common glasses contain

impurity ions such as Na+, Ca2+, Al3+, and B3+

(soda glass)Adapted from Fig. 12.11, Callister & Rethwisch 8e.

Glass Structure

Si04 tetrahedron4-

Si4+

O2-

Si4+Na+

O2-

Chapter 13 -12

• Specific volume (1/ρ) vs Temperature (T):

• Glasses: -- do not crystallize-- change in slope in spec. vol. curve at

glass transition temperature, Tg-- transparent - no grain boundaries to

scatter light

• Crystalline materials: -- crystallize at melting temp, Tm-- have abrupt change in spec.

vol. at Tm


Glass Properties

T

Specific volume

Supercooled Liquid

solid

Tm

Liquid(disordered)

Crystalline (i.e., ordered)

Tg

Glass (amorphous solid)

Chapter 13 -13

Glass Properties: Viscosity

• Viscosity, η: -- relates shear stress (τ) and velocity gradient (dv/dy):

η has units of (Pa-s)

dydv /τ

=η

velocity gradient

dvdy

τ

τ

glass dvdy

Chapter 13 -14

Visc

osity

[Pa-

s]

1102

106

1010

1014

200 600 1000 1400 1800 T(ºC)

Working range: glass-forming carried out

annealing point

Tmelt

strain point

• Viscosity decreases with T

Adapted from Fig. 13.7, Callister & Rethwisch 8e. (Fig. 13.7 is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.)

Log Glass Viscosity vs. Temperature

• fused silica: > 99.5 wt% SiO2

• soda-lime glass: 70% SiO2balance Na2O (soda) & CaO (lime)

• Vycor: 96% SiO2, 4% B2O3

• borosilicate (Pyrex): 13% B2O3, 3.5% Na2O, 2.5% Al2O3

Chapter 13 -15

• Annealing:-- removes internal stresses caused by uneven cooling.

• Tempering:-- puts surface of glass part into compression-- suppresses growth of cracks from surface scratches.-- sequence:

Heat Treating Glass

at room temp.

tensioncompression

compression

before cooling

hot

initial cooling

hotcooler

cooler

-- Result: surface crack growth is suppressed.

Chapter 13 -16

• Mill (grind) and screen constituents: desired particle size• Extrude this mass (e.g., into a brick)

• Dry and fire the formed piece

ram billet

container

containerforce die holder

die

Ao

AdextrusionAdapted from Fig. 12.8(c), Callister & Rethwisch 8e.

Ceramic Fabrication Methods (iia)

GLASSFORMING

PARTICULATEFORMING

CEMENTATION

Hydroplastic forming:

Chapter 13 -17

• Mill (grind) and screen constituents: desired particle size

• Slip casting operation

• Dry and fire the cast piece

Ceramic Fabrication Methods (iia)

solid component

Adapted from Fig. 13.12, Callister & Rethwisch 8e. (Fig. 13.12 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

hollow component

pour slip into mold

drain mold

“green ceramic”

pour slip into mold

absorb water into mold “green

ceramic”

GLASSFORMING

PARTICULATEFORMING

CEMENTATION

Slip casting:

• Mix with water and other constituents to form slip

Chapter 13 -18

Typical Porcelain Composition

(50%) 1. Clay(25%) 2. Filler – e.g. quartz (finely ground)(25%) 3. Fluxing agent (Feldspar)

-- aluminosilicates plus K+, Na+, Ca+

-- upon firing - forms low-melting-temp. glass

Chapter 13 -19

• Clay is inexpensive• When water is added to clay

-- water molecules fit in between layered sheets

-- reduces degree of van der Waals bonding

-- when external forces applied – clay particles free to move past one another – becomes hydroplastic

• Structure ofKaolinite Clay:

Adapted from Fig. 12.14, Callister & Rethwisch 8e. (Fig. 12.14 is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.)

Hydroplasticity of Clay

weak van der Waals bonding

charge neutral

charge neutral

Si 4+

Al 3+-OH

O2-

Shear

Shear

Chapter 13 -20

• Drying: as water is removed - interparticle spacings decrease – shrinkage .

Adapted from Fig. 13.13, Callister & Rethwisch 8e. (Fig. 13.13 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

Drying and Firing

Drying too fast causes sample to warp or crack due to non-uniform shrinkagewet body partially dry completely dry

• Firing:-- heat treatment between

900-1400ºC-- vitrification: liquid glass forms

from clay and flux – flows between SiO2 particles. (Flux lowers melting temperature). Adapted from Fig. 13.14, Callister & Rethwisch 8e.

(Fig. 13.14 is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.)

Si02 particle(quartz)

glass formed around the particle

mic

rogr

aph

of p

orce

lain

70µm

Chapter 13 -21

Powder Pressing: used for both clay and non-clay compositions.

• Powder (plus binder) compacted by pressure in a mold-- Uniaxial compression - compacted in single direction-- Isostatic (hydrostatic) compression - pressure applied by

fluid - powder in rubber envelope-- Hot pressing - pressure + heat

Ceramic Fabrication Methods (iib)

GLASSFORMING

PARTICULATEFORMING

CEMENTATION

Chapter 13 -22

Sintering


Aluminum oxide powder:-- sintered at 1700ºC

for 6 minutes.Adapted from Fig. 13.17, Callister & Rethwisch 8e. (Fig. 13.17 is from W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, Introduction to Ceramics, 2nd ed., John Wiley and Sons, Inc., 1976, p. 483.)

15µm

Sintering occurs during firing of a piece that has been powder pressed-- powder particles coalesce and reduction of pore size

Chapter 13 -23

Tape Casting• Thin sheets of green ceramic cast as flexible tape• Used for integrated circuits and capacitors• Slip = suspended ceramic particles + organic liquid

(contains binders, plasticizers)

Fig. 13.18, Callister & Rethwisch 8e.

Chapter 13 -24

• Hardening of a paste – paste formed by mixing cement material with water

• Formation of rigid structures having varied and complex shapes

• Hardening process – hydration (complex chemical reactions involving water and cement particles)

Ceramic Fabrication Methods (iii)

GLASSFORMING

PARTICULATEFORMING

CEMENTATION

• Portland cement – production of:-- mix clay and lime-bearing minerals-- calcine (heat to 1400ºC)-- grind into fine powder

Chapter 13 -25

• Categories of ceramics: -- glasses -- clay products-- refractories -- cements-- advanced ceramics

• Ceramic Fabrication techniques:-- glass forming (pressing, blowing, fiber drawing).-- particulate forming (hydroplastic forming, slip casting,

powder pressing, tape casting)-- cementation

• Heat treating procedures-- glasses—annealing, tempering-- particulate formed pieces—drying, firing (sintering)

Summary

Chapter 14 - 1

ISSUES TO ADDRESS...• What are the general structural and chemical

characteristics of polymer molecules?• What are some of the common polymeric

materials, and how do they differ chemically?• How is the crystalline state in polymers different

from that in metals and ceramics ?

Chapter 14:Polymer Structures

Chapter 14 - 2

What is a Polymer?

Poly mermany repeat unit


C C C C C CHHHHHH

HHHHHH

Polyethylene (PE)ClCl Cl

C C C C C CHHH

HHHHHH

Poly(vinyl chloride) (PVC)HH

HHH H

Polypropylene (PP)

C C C C C CCH3

HH

CH3CH3H

repeatunit

repeatunit

repeatunit

Chapter 14 - 3

Ancient Polymers• Originally natural polymers were used

– Wood – Rubber– Cotton – Wool– Leather – Silk

• Oldest known uses– Rubber balls used by Incas– Noah used pitch (a natural polymer)

for the ark

Chapter 14 - 4

Polymer CompositionMost polymers are hydrocarbons

– i.e., made up of H and C• Saturated hydrocarbons

– Each carbon singly bonded to four other atoms– Example:

• Ethane, C2H6

C C

H

H H H

HH

Chapter 14 - 5

Chapter 14 - 6

Unsaturated Hydrocarbons• Double & triple bonds somewhat unstable –

can form new bonds– Double bond found in ethylene or ethene - C2H4

– Triple bond found in acetylene or ethyne - C2H2

C CH

H

H

H

C C HH

Chapter 14 - 7

Isomerism• Isomerism

– two compounds with same chemical formula can have quite different structures

for example: C8H18• normal-octane

• 2,4-dimethylhexane

C C C C C C C CH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3=

H3C CH

CH3

CH2 CH

CH2

CH3

CH3

H3C CH2 CH3( )6

⇓

Chapter 14 - 8

Polymerization and Polymer Chemistry

• Free radical polymerization

• Initiator: example - benzoyl peroxide

C

H

H

O O C

H

H

C

H

H

O2

C C

H H

HHmonomer(ethylene)

R +

free radical

R C C

H

H

H

H

initiation

R C C

H

H

H

H

C C

H H

HH

+ R C C

H

H

H

H

C C

H H

H H

propagation

dimer

R= 2

Chapter 14 - 9

Chemistry and Structure of Polyethylene


Note: polyethylene is a long-chain hydrocarbon- paraffin wax for candles is short polyethylene

Chapter 14 -10

Bulk or Commodity Polymers

Chapter 14 -11

Bulk or Commodity Polymers (cont)

Chapter 14 -12

Bulk or Commodity Polymers (cont)

Chapter 14 -

VMSE: Polymer Repeat Unit Structures

13

Manipulate and rotate polymer structures in 3-dimensions

Chapter 14 -14

MOLECULAR WEIGHT• Molecular weight, M: Mass of a mole of chains.

Low M

high M

Not all chains in a polymer are of the same length— i.e., there is a distribution of molecular weights

Chapter 14 -15

xi = number fraction of chains in size range i

molecules of #totalpolymer of wttotal

=nM

MOLECULAR WEIGHT DISTRIBUTION

Mn = ΣxiMi

Mw = ΣwiMi


wi = weight fraction of chains in size range i

Mi = mean (middle) molecular weight of size range i

Chapter 14 -16

Molecular Weight Calculation

Example: average mass of a classStudent Weight

mass (lb)1 1042 1163 1404 1435 1806 1827 1918 2209 22510 380

What is the averageweight of the students inthis class:a) Based on the number

fraction of students in each mass range?

b) Based on the weight fraction of students in each mass range?

Chapter 14 -17

Molecular Weight Calculation (cont.)Solution: The first step is to sort the students into weight ranges.

Using 40 lb ranges gives the following table:

weight number of mean number weightrange students weight fraction fraction

Ni Wi xi wi

mass (lb) mass (lb)81-120 2 110 0.2 0.117

121-160 2 142 0.2 0.150161-200 3 184 0.3 0.294201-240 2 223 0.2 0.237241-280 0 - 0 0.000281-320 0 - 0 0.000321-360 0 - 0 0.000361-400 1 380 0.1 0.202

ΣNi ΣNiWi

10 1881total

numbertotal

weight

Calculate the number and weight fraction of students in each weight range as follows:

xi =Ni

Ni∑

wi =NiWi

NiWi∑

For example: for the 81-120 lb range

x81−120 =2

10= 0.2

117.01881

011 x 212081 ==−w

Chapter 14 -18

Molecular Weight Calculation (cont.)

Mn = xiMi∑ = (0.2 x 110 + 0.2 x 142 + 0.3 x 184 + 0.2 x 223 + 0.1 x 380) =188 lb

weight mean number weightrange weight fraction fraction

Wi xi wi

mass (lb) mass (lb)81-120 110 0.2 0.117

121-160 142 0.2 0.150161-200 184 0.3 0.294201-240 223 0.2 0.237241-280 - 0 0.000281-320 - 0 0.000321-360 - 0 0.000361-400 380 0.1 0.202

Mw = wiMi∑ = (0.117 x 110 + 0.150 x 142 + 0.294 x 184

+ 0.237 x 223 + 0.202 x 380) = 218 lb

Mw = wiMi∑ = 218 lb

Chapter 14 -19

Degree of Polymerization, DPDP = average number of repeat units per chain

iimfm

m

Σ=

=

:follows as calculated is this copolymers forunit repeat of weightmolecular average where

C C C C C C C CH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C C C C

H

H

H

H

H

H

H

H

H( ) DP = 6

mol. wt of repeat unit iChain fraction

mMDP n=

Chapter 14 -20


Molecular Structures for Polymers

Branched Cross-Linked NetworkLinear

secondarybonding

Chapter 14 -21

Polymers – Molecular ShapeMolecular Shape (or Conformation) – chain

bending and twisting are possible by rotation of carbon atoms around their chain bonds– note: not necessary to break chain bonds

to alter molecular shape


Chapter 14 -22

Chain End-to-End Distance, r


Chapter 14 -23

Molecular Configurations for Polymers

Configurations – to change must break bonds• Stereoisomerism

EB

A

D

C C

D

A

BE

mirror plane

C CR

HH

HC C

H

H

H

R

or C C

H

H

H

R

Stereoisomers are mirrorimages – can’t superimposewithout breaking a bond

Chapter 14 -24

TacticityTacticity – stereoregularity or spatial arrangement of R

units along chain

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

isotactic – all R groups on same side of chain

C C

H

H

H

R

C C

H

H

H

R

C C

H

H

H

R R

H

H

H

CC

syndiotactic – R groups alternate sides

Chapter 14 -25

Tacticity (cont.)

atactic – R groups randomlypositioned

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

Chapter 14 -26

cis/trans Isomerism

C CHCH3

CH2 CH2

C CCH3

CH2

CH2

H

ciscis-isoprene

(natural rubber)

H atom and CH3 group on same side of chain

transtrans-isoprene (gutta percha)

H atom and CH3 group on opposite sides of chain

Chapter 14 -

VMSE: Stereo and Geometrical Isomers

27Chapter 7 - 19

Manipulate and rotate polymer structures in 3-dimensions

Chapter 14 -28

Copolymerstwo or more monomers

polymerized together • random – A and B randomly

positioned along chain• alternating – A and B

alternate in polymer chain• block – large blocks of A

units alternate with large blocks of B units

• graft – chains of B units grafted onto A backbone

A – B –

random

block

graft


alternating

Chapter 14 -29

Crystallinity in Polymers• Ordered atomic

arrangements involving molecular chains

• Crystal structures in terms of unit cells

• Example shown– polyethylene unit cell


Chapter 14 -30

Polymer Crystallinity• Crystalline regions

– thin platelets with chain folds at faces– Chain folded structure

10 nm


Chapter 14 -31

Polymer Crystallinity (cont.)Polymers rarely 100% crystalline• Difficult for all regions of all chains to

become aligned

• Degree of crystallinity expressed as % crystallinity.-- Some physical properties

depend on % crystallinity.-- Heat treating causes

crystalline regions to grow and % crystallinity to increase.

Adapted from Fig. 14.11, Callister 6e.(Fig. 14.11 is from H.W. Hayden, W.G. Moffatt,and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.)

crystalline region

amorphousregion

Chapter 14 -32

Polymer Single Crystals• Electron micrograph – multilayered single crystals

(chain-folded layers) of polyethylene• Single crystals – only for slow and carefully controlled

growth rates


Chapter 14 -33

Semicrystalline Polymers

Spherulite surface


• Some semicrystalline polymers form spherulite structures

• Alternating chain-folded crystallites and amorphous regions

• Spherulite structure for relatively rapid growth rates

Chapter 14 -34

Photomicrograph – Spherulites in Polyethylene


Cross-polarized light used -- a maltese cross appears in each spherulite

Chapter 11: Applications and Processing of Metal Alloys

Documents

Transcript of Chapter 11: Applications and Processing of Metal Alloys