SYNTHESIS, FABRICATION, AND PROCESSING OF MATERIALS

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SYNTHESIS, FABRICATION, AND PROCESSING OF
MATERIALS
ISSUES TO ADDRESS...

• What are the common fabrication techniques for
  metals?
• How do the properties vary throughout a piece of
  metal that
• has 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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REFINEMENT OF STEEL FROM ORE
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METAL FABRICATION METHODS-I
FORMING
Forging (wrenches, crankshafts)
Rolling (I-beams, rails)
often at elev. T
Adapted from Fig. 11.7, Callister 6e.
Drawing (rods, wire, tubing)
Extrusion (rods, tubing)
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FORMING TEMPERATURE
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!
--Swaged
(a)
(b)
(c)
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.)
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METAL FABRICATION METHODS-II
CASTING
Sand Casting (large parts, e.g.,
auto engine blocks)
Die Casting (high volume, low T alloys)
Continuous Casting (simple slab shapes)
Investment Casting (low volume, complex
shapes e.g., jewelry, turbine blades)
plaster die formed around wax prototype
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METAL FABRICATION METHODS-III
JOINING
Powder Processing (materials w/low
ductility)
Welding (when one large part is
impractical)
Adapted from Fig. 11.8, Callister 6e. (Fig. 11.8
from Iron Castings Handbook, C.F. Walton and T.J.
Opar (Ed.), 1981.)
Heat affected zone (region in which the
microstructure has been changed).
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THERMAL PROCESSING OF METALS
Annealing Heat to Tanneal, then cool slowly.
Based on discussion in Section 11.7, Callister 6e.
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HARDENABILITY--STEELS
Ability to form martensite Jominy end
quench test to measure hardenability.
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.)
Hardness versus distance from the quenched end.
Adapted from Fig. 11.11, Callister 6e.
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WHY HARDNESS CHANGES W/POSITION
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.)
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HARDENABILITY VS ALLOY CONTENT
Jominy end quench results, C 0.4wtC
Adapted from Fig. 11.13, Callister 6e. (Fig.
11.13 adapted from figure furnished courtesy
Republic Steel Corporation.)
"Alloy Steels" (4140, 4340, 5140, 8640)
--contain Ni, Cr, Mo (0.2 to 2wt)
--these elements shift the "nose".
--martensite is easier to form.
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QUENCHING MEDIUM GEOMETRY
Effect of quenching medium
Medium air oil water
Hardness small moderate large
Severity of Quench small moderate large
Effect of geometry When surface-to-volume
ratio increases --cooling rate
increases --hardness increases
Position center surface
Cooling rate small large
Hardness small large
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PREDICTING HARDNESS PROFILES
Ex Round bar, 1040 steel, water quenched, 2"
diam.
Adapted from Fig. 11.18, Callister 6e.
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CERAMIC FABRICATION METHODS-I
GLASS FORMING
Pressing
Fiber drawing
Blowing
Adapted from Fig. 13.7, Callister, 6e. (Fig.
13.7 is adapted from C.J. Phillips, Glass The
Miracle Maker, Pittman Publishing Ltd., London.)
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GLASS STRUCTURE
Basic Unit
Glass is amorphous Amorphous structure
occurs by adding impurities (Na,Mg2,Ca2,
Al3) Impurities interfere with formation
of crystalline structure.
Quartz is crystalline SiO2
(soda glass)
Adapted from Fig. 12.11, Callister, 6e.
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GLASS PROPERTIES
Specific volume (1/r) vs Temperature (T)
Crystalline materials --crystallize at
melting temp, Tm --have abrupt change in
spec. vol. at Tm
Glasses --do not crystallize --spec.
vol. varies smoothly with T --Glass
transition temp, Tg
Adapted from Fig. 13.5, Callister, 6e.
Viscosity --relates shear stress
velocity gradient --has units of (Pa-s)
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GLASS VISCOSITY VS T AND IMPURITIES
Viscosity decreases with T Impurities lower
Tdeform
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.)
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HEAT TREATING GLASS
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.
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CERAMIC FABRICATION METHODS-IIA
PARTICULATE FORMING
Milling and screening desired particle size
Mixing particles water produces a "slip"
Form a "green" component
Adapted from Fig. 11.7, Callister 6e.
--Hydroplastic forming extrude the slip
(e.g., into a pipe)
--Slip casting
Adapted from Fig. 13.10, Callister 6e. (Fig.
13.10 is from W.D. Kingery, Introduction to
Ceramics, John Wiley and Sons, Inc., 1960.)
hollow component
solid component
Dry and Fire the component
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FEATURES OF A SLIP
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
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.)
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DRYING AND FIRING
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.)
Firing --T raised to (900-1400 C)
--vitrification glass forms from clay and flows
between SiO2 particles.
Adapted from Fig. 13.12, Callister 6e. (Fig.
13.12 is courtesy H.G. Brinkies, Swinburne
University of Technology, Hawthorn Campus,
Hawthorn, Victoria, Australia.)
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CERAMIC FABRICATION METHODS-IIB
PARTICULATE FORMING
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.
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.)
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CERAMIC FABRICATION METHODS-III
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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SUMMARY

• 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

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