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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?
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Metal Alloys
Ferrous Nonferrous
Cu Al Mg Ti
2
Adapted from
Fig. 11.1,
Callister 7e.
Adapted from Fig. 9.24,Callister 7e.
(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.)
Steels
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Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister 7e.
Low Alloy High Alloylow carbon
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Nomenclature AISI & SAE10xx 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 100example: 1060 steel plain carbon steel with 0.60 wt% C
Stainless Steel -- >11% Cr
4
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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
5
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Graphite formation
promoted by
Si > 1 wt%
slow cooling
Adapted from Fig.
11.2,Callister 7e. (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
g
+L
a+ Graphite
Liquid +
Graphite
(Fe) Co, wt% C
0.6
5 740C
T(C)
g+ Graphite
100
1153Cg
Austenite 4.2 wt% C
a + g
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White iron
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Adapted from Fig.11.5,
Callister 7e.
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1) Relatively high density
2) Relatively low conductivity3) Poor corrosion resistance
10
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Based on discussion and data provided in Section 11.3, Callister 7e.
NonFerrousAlloys
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 AlloysBrass:Zn is subst. impurity(costume jewelry, coins,corrosion resistant)Bronze : Sn, Al, Si, Ni are
subst. impurity(bushings, landinggear)Cu-Be:precip. hardened
for strength
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FORMING CASTING JOINING
Rough stock formed to final shape through
plastic deformation
Hot working vs. Cold working
Thigh enough for well below Tmrecrystallization work hardening
Larger deformations smaller deformations
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FORMING
Ao Ad
force
die
blank
force
often atelev. T
Adapted from Fig.
11.8, Callister 7e.
CASTING JOINING
Forging (Hammering; Stamping)
(wrenches, crankshafts)
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FORMING
roll
A o
A d
roll
CASTING JOINING
Rolling (Hot or Cold Rolling)
(I-beams, rails, sheet & plate)
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FORMING
tensile
forceA
o
Addie
die
die must be well lubricated & clean
CASTING JOINING
Drawing(rods, wire, tubing)
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FORMING
ram billet
container
container
force die holder
die
Ao
Adextrusion
CASTING JOINING
Extrusion
(rods, tubing) - ductile metals, e.g. Cu, Al (hot)
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FORMING CASTING JOINING
most common, cheapest method
gives good production of shapes
weaker products, internal defects
good option for brittle materials
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Sand Casting
(large parts, e.g. auto engine blocks) can withstand >1600C
pack sand around form (pattern) of desired shape
Sand Sand
molten metal
FORMING CASTING JOINING
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plaster
die formed
around wax
prototype
Investment Casting(low volume, complex shapes e.g., jewelry, turbine blades)
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
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Die Casting(high volume, low T alloys) Continuous Casting(simple slab shapes)
molten
solidified
FORMING CASTING JOINING
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CASTING JOINING
Powder Metallurgy
(materials w/low ductility)
pressure
heat
point contactat low T
densificationby diffusion at
higherT
areacontact
densify
Welding
(when one large part is
impractical)
Heat affected zone:
(region in which the
microstructure has been
changed).
Adapted from Fig.
11.9, Callister 7e.
(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)
unaffectedunaffected
heat affected zone
FORMING
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Annealing: Heat to Tanneal, then cool slowly.
Based on discussion in Section 11.7, Callister 7e.
Types of
Annealing
Process Anneal:
Negate effect ofcold working by(recovery/
recrystallization)
Stress Relief: Reducestress caused by:
-plastic deformation-nonuniform cooling-phase transform.
Normalize (steels):Deform steel with largegrains, then normalizeto make grains small.
Full Anneal (steels):Make soft steels forgood forming by heatingto get g, then cool in
furnace to get coarse P.
Spheroidize (steels):Make very soft steels forgood machining. Heat just
below TE& hold for
15-25h.
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Ability to form martensite Jominy end quench test to measure hardenability.
Hardness versus distance from the quenched end.
Adapted from Fig. 11.11,
Callister 7e. (Fig. 11.11
adapted from A.G. Guy,
Essentials of MaterialsScience, McGraw-Hill Book
Company, New York,
1978.)
Adapted from Fig. 11.12,
Callister 7e.
24C water
specimen(heated to gphase field)
flat ground
Rockwell C
hardness tests
Hardness,
HRC
Distance from quenched end
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Effect of quenching medium:
Medium
air
oil
water
Severity of Quench
low
moderate
high
Hardness
low
moderate
high
Effect of geometry:
When surface-to-volume ratio increases:
--cooling rate increases
--hardness increasesPosition
center
surface
Cooling rate
low
high
Hardness
low
high
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0 10 20 30 40 50wt% Cu
La+La
a+qq
q+L
300
400
500
600
700
(Al)
T(C)
composition rangeneeded for precipitation hardening
CuAl2
A
Adapted from Fig. 11.24, Callister 7e. (Fig. 11.24 adapted from J.L.
Murray, International Metals Review30, p.5, 1985.)
Particles impede dislocations.
Ex: Al-Cu system Procedure:
Adapted from Fig.
11.22, Callister 7e.
--Pt B: quench to room temp.
--Pt C: reheat to nucleatesmall q crystals within
a crystals.
Other precipitation
systems: Cu-Be
Cu-Sn
Mg-Al
Temp.
Time
--Pt A: solution heat treat
(get a solid solution)
Pt A (soln heat treat)
B
Pt B
C
Pt C (precipitate q)
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2014 Al Alloy:
TS peaks with
precipitation time.
Increasing Taccelerates
process.
Adapted from Fig. 11.27 (a) and (b), Callister 7e. (Fig. 11.27 adapted from Metals Handbook:
Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th ed., H. Baker (ManagingEd.), American Society for Metals, 1979. p. 41.)
precipitation heat treat timetensilestrength(MPa)
200
300
400
1001min 1h 1day 1mo 1yr
204C149C
%EL reaches minimum
with precipitation time.
%EL(2
insample)
10
20
30
01min 1h 1day 1mo 1yr
204C149C
precipitation heat treat time
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Alloys substitutional alloys
can be ordered or disordered disordered solid solution
ordered - periodic substitution
example: CuAu FCC
27
Cu
Au
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Interstitial alloys (compounds)
one metal much larger than the other
smaller metal goes in ordered way intointerstitial holes in the structure of largermetal
Ex: Cementite Fe3C
28
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Consider FCC structure --- what types of holes
are there?
29
Octahedron - octahedral site = OH Tetrahedron - tetrahedral site = TD
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Interstitials such as H, N, B, C FCC has 4 atoms per unit cell
metal atoms
21
21
21
21
TD sites
43
41
,43
41
,
43
41
,43
41
,
8 TD sites
OHsites
21
21
21
21
2
1
4 OH sites