ISSUES TO ADDRESS...

• What are the common fabrication techniques for metals?

• How do the properties vary throughout a piece of metal thathas been quenched?

• How can properties be modified by a post heat treatment?

• How is the processing of ceramics different than for metals?

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CHAPTER 14:SYNTHESIS, FABRICATION, AND

PROCESSING OF MATERIALS

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Iron OreCoke

Limestone

3CO+Fe2O3 2Fe+3CO2

C+O2 CO2

CO2+C2CO

CaCO3 CaO+CO2CaO + SiO2 +Al2O3 slag

purification

reduction of iron ore to metal

heat generation

Molten iron

BLAST FURNACE

slagair

layers of coke and iron ore

gasrefractory vessel

REFINEMENT OF STEEL FROM ORE

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force

dieblank

force

• Forging (wrenches, crankshafts)

CASTING JOININGFORMING

• Drawing (rods, wire, tubing)

often atelev. T

• Rolling (I-beams, rails)

• Extrusion (rods, tubing)

Adapted from Fig. 11.7, Callister 6e.

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die holder

die

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Adextrusion

roll

AoAd

roll

tensile force

AoAddie

die

METAL FABRICATION METHODS-I

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• Hot working --recrystallization --less energy to deform --oxidation: poor finish --lower strength

• Cold working --recrystallization --less energy to deform --oxidation: poor finish --lower strength

• Cold worked microstructures --generally are very anisotropic!

--Forged --Fracture resistant!

Reprinted w/ permission from R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials", (4th ed.), John Wiley and Sons, Inc., 1996. (a) Fig. 10.5, p. 410 (micrograph courtesy of G. Vander Voort, Car Tech Corp.); (b) Fig. 10.6(b), p. 411 (Orig. source: J.F. Peck and D.A. Thomas, Trans. Metall. Soc. AIME, 1961, p. 1240); (c) Fig. 10.10, p. 415 (Orig. source: A.J. McEvily, Jr.and R.H. Bush, Trans. ASM 55, 1962, p. 654.)

(a) (b) (c)

--Swaged

FORMING TEMPERATURE

plasterdie formedaround waxprototype

FORMING JOINING

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

Sand Sand

molten metal

• Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades)

wax

• Die Casting (high volume, low T alloys)

• Continuous Casting (simple slab shapes)

molten

solidified

METAL FABRICATION METHODS-II

6

CASTINGFORMING JOINING• Powder Processing (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).

Adapted from Fig. 11.8, Callister 6e.(Fig. 11.8 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

METAL FABRICATION METHODS-III

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Annealing: Heat to Tanneal, then cool slowly.

Types of Annealing

• Process Anneal: Negate effect of cold working by (recovery/ recrystallization)

• Stress Relief: Reduce stress caused by:

-plastic deformation -nonuniform cooling -phase transform.

• Normalize (steels): Deform steel with large grains, then normalize to make grains small.

• Full Anneal (steels): Make soft steels for good forming by heating to get , then cool in furnace to get coarse P.

• Spheroidize (steels): Make very soft steels for good machining. Heat just below TE & hold for 15-25h.

Based on discussion in Section 11.7, Callister 6e.

THERMAL PROCESSING OF METALS

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• Ability to form martensite• Jominy end quench test to measure hardenability.

• Hardness versus distance from the quenched end.

24°C water

specimen (heated to phase field)

flat ground

4”

1”

Hard

ness

, H

RC

Distance from quenched end

Adapted from Fig. 11.10, Callister 6e. (Fig. 11.10 adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.)

Adapted from Fig. 11.11, Callister 6e.

HARDENABILITY--STEELS

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• The cooling rate varies with position.

Adapted from Fig. 11.12, Callister 6e. (Fig. 11.12 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.)

WHY HARDNESS CHANGES W/POSITION

distance from quenched end (in)Ha

rdn

ess

, HR

C

20

40

60

0 1 2 3

600

400

200A M

A P

Martensite

Martensite +

Pearlite

Fine Pearlite

Pearlite

0.1 1 10 100 1000

T(°C)

M(start)

Time (s)

0

0%100%

M(finish)

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• Jominy end quench results, C = 0.4wt%C

• "Alloy Steels" (4140, 4340, 5140, 8640) --contain Ni, Cr, Mo (0.2 to 2wt%) --these elements shift the "nose". --martensite is easier to form.

Adapted from Fig. 11.13, Callister 6e. (Fig. 11.13 adapted from figure furnished courtesy Republic Steel Corporation.)

T(°C)

10-1 10 103 1050

200

400

600

800

Time (s)

M(start)M(90%)

TE

A Bshift from A to B due to alloying

HARDENABILITY VS ALLOY CONTENTCooling rate (°C/s)

Hard

ness

, H

RC

20

40

60

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

210100 3

4140

8640

5140

1040

50

80

100

%M4340

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• Effect of quenching medium:

Mediumairoil

water

Severity of Quenchsmall

moderatelarge

Hardnesssmall

moderatelarge

• Effect of geometry: When surface-to-volume ratio increases: --cooling rate increases --hardness increases

Positioncentersurface

Cooling ratesmalllarge

Hardnesssmalllarge

QUENCHING MEDIUM & GEOMETRY

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• Ex: Round bar, 1040 steel, water quenched, 2" diam.

20

40

60

20

40

60

0

2

4

0 1

2 in.

0 10.5 1.5 2

Bar Diameter (in)

centerR/2R

1040

effective distance from quenched end (in)

effective distance from quenched end (in)

Hardness, HRC

center = 27HRCR/2 = 30HRC

R = 54HRC

Hardness profile

0.5

HRC

Adapted from Fig. 11.18, Callister 6e.

PREDICTING HARDNESS PROFILES

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• Pressing:

PARTICULATE FORMING

CEMENTATIONGLASSFORMING

Gob

Parison mold

Pressing operation

• Blowing:

• Fiber drawing:

suspended Parison

Finishing mold

Compressed air

Adapted from Fig. 13.7, Callister, 6e. (Fig. 13.7 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)

CERAMIC FABRICATION METHODS-I

wind up

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• Quartz is crystalline SiO2: Si4+

Na+

O2-

• Basic Unit:

Si04 tetrahedron4-

Si4+

O2-

• Glass is amorphous• Amorphous structure occurs by adding impurities

(Na+,Mg2+,Ca2+, Al3+)• Impurities: interfere with formation of crystalline structure.

(soda glass)Adapted from Fig. 12.11, Callister, 6e.

GLASS STRUCTURE

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

Glass (amorphous solid)

T

Specific volume

Liquid (disordered)Supercooled

Liquid

Crystalline (i.e., ordered) solid

TmTg

• Glasses: --do not crystallize --spec. vol. varies smoothly with T --Glass transition temp, Tg

• Crystalline materials: --crystallize at melting temp, Tm

--have abrupt change in spec. vol. at Tm

• Viscosity: --relates shear stress & velocity gradient: --has units of (Pa-s)

dvdy

velocity gradient

dvdy

glass dv

dy

Adapted from Fig. 13.5, Callister, 6e.

GLASS PROPERTIES

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• Viscosity decreases with T• Impurities lower Tdeform

Vis

cosi

ty [

Pa

s]

1

102

106

1010

1014

200 600 1000 1400 1800 T(°C)

Tdeform: soft enough to deform or “work”

annealing range

fused silica

96% silica

Pyrex

soda-lime

glass

Adapted from Fig. 13.6, Callister, 6e.(Fig. 13.6 is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.)

GLASS VISCOSITY VS T AND IMPURITIES

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• Annealing: --removes internal stress caused by uneven cooling.• Tempering: --puts surface of glass part into compression --suppresses growth of cracks from surface scratches. --sequence:

--Result: surface crack growth is suppressed.

further cooledbefore cooling surface cooling

tensioncompression

compressionhot hot

cooler

cooler

HEAT TREATING GLASS

• Milling and screening: desired particle size

GLASS FORMING

CEMENTATIONPARTICULATEFORMING

• Mixing particles & water: produces a "slip"

--Hydroplastic forming: extrude the slip (e.g., into a pipe)

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• Form a "green" component

hollow component

pour slip into mold

absorb water into mold “green

ceramic”

pour slip into mold

drain mold

“green ceramic”

• Dry and Fire the component

--Slip casting:

solid component

Adapted from Fig. 11.7, Callister 6e.

Adapted from Fig. 13.10, Callister 6e.(Fig. 13.10 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

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die

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Adextrusion

CERAMIC FABRICATION METHODS-IIA

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• Clay is inexpensive• Adding water to clay --allows material to shear easily along weak van der Waals bonds --enables extrusion --enables slip casting

• Structure ofKaolinite Clay:

weak van der Waals bonding

charge neutral

charge neutral

Si4+

Al3+

-OHO2-

Shear

Shear

Adapted from Fig. 12.14, Callister 6e.(Fig. 12.14 is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.)

FEATURES OF A SLIP

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wet slip partially dry “green” ceramic

• Firing: --T raised to (900-1400 C) --vitrification: glass forms from clay and flows between SiO2 particles.

• Drying: layer size and spacing decrease.Adapted from Fig. 13.11, Callister 6e.(Fig. 13.11 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

Adapted from Fig. 13.12, Callister 6e.(Fig. 13.12 is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.)

Si02 particle (quartz)

glass formed around the particle

micrograph of porcelain

70m

DRYING AND FIRING

• Sintering: useful for both clay and non-clay compositions.• Procedure: --grind to produce ceramic and/or glass particles --inject into mold --press at elevated T to reduce pore size.• Aluminum oxide powder: --sintered at 1700C for 6 minutes.

GLASS FORMING

CEMENTATIONPARTICULATEFORMING

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Adapted from Fig. 13.15, Callister 6e.(Fig. 13.15 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.)

15m

CERAMIC FABRICATION METHODS-IIB

PARTICULATE FORMING

GLASS FORMING

CEMENTATION

• Produced in extremely large quantities.• Portland cement: --mix clay and lime bearing materials --calcinate (heat to 1400C) --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.

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CERAMIC FABRICATION METHODS-III

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• Fabrication techniques for metals- Forming, casting, joining

• Hardenability- Increases with alloy content

• Fabrication techniques for ceramics- 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 in compression

SUMMARY

Reading:

Core Problems:

Self-help Problems:

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