Chapter 11: Metal Alloys
Applications and Processing
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 - 1
Taxonomy of Metals
Metal Alloys
Ferrous
Steels
Steels
<1.4wt%C
<1.4
wt% C
Cast Irons
Cast
Irons
3-4.5
wt%C
3-4.5 wt% C
Cu
Al
1600
d
L
1400
g
austenite
g+L
a800
ferrite
600
400
0
(Fe)
L+Fe3C
1148°C
4.30
1000
727°C
Eutectoid:
0.76
1
2
Eutectic:
g+Fe3C
4
Ti
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.)
Fe3C
cementite
a+Fe3C
3
Mg
microstructure:
ferrite, graphite
cementite
T(°C)
1200
Adapted from
Fig. 11.1,
Callister 7e.
Nonferrous
5
6
Co , wt% C
6.7
Chapter 11 - 2
Steels
High Alloy
Low Alloy
low carbon Med carbon
<0.25 wt% C 0.25-0.6wt% C
high carbon
0.6-1.4wt% C
heat
plain
treatable
Cr,V
Cr, Ni
Additions none
none
none
Ni, Mo
Mo
Example 1010 4310
1040
4340 1095
Hardenability 0
+
+
++
++
TS
0
+
++
+
EL
+
+
0
Name
plain
Uses
auto
struc.
sheet
HSLA
bridges
towers
press.
vessels
plain
crank
shafts
bolts
hammers
blades
pistons
gears
wear
applic.
wear
applic.
tool
Cr, V,
Mo, W
4190
+++
++
-drills
saws
dies
increasing strength, cost, decreasing ductility
Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister 7e.
austenitic
stainless
Cr, Ni, Mo
304
0
0
++
high T
applic.
turbines
furnaces
V. corros.
resistant
Chapter 11 - 3
Refinement of Steel from Ore
Coke
Iron Ore
gas
refractory
vessel
layers of coke
and iron ore
air
slag
Molten iron
Limestone
BLAST FURNACE
heat generation
C+O2 CO2
reduction of iron ore to metal
CO2 + C  2CO
3CO + Fe2O3 2Fe+3CO2
purification
CaCO3  CaO+CO2
CaO + SiO2 + Al2O3  slag
Chapter 11 - 4
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
Chapter 11 - 5
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
Chapter 11 - 6
Fe-C True Equilibrium Diagram
T(°C)
1600
Graphite formation
promoted by
1400
• Si > 1 wt%
1200
• slow cooling
L
g
Austenite
Liquid +
Graphite
g +L
1153°C
4.2 wt% C
1000
g + Graphite
a+g
800
0.65
740°C
600
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.)
400
(Fe)
a + Graphite
0
1
2
3
4
90
Co , wt% C
Chapter 11 - 7
100
Types of Cast Iron
Gray iron
• graphite flakes
• weak & brittle under tension
• stronger under compression
• excellent vibrational dampening
• wear resistant
Adapted from Fig. 11.3(a) & (b), Callister 7e.
Ductile iron
• add Mg or Ce
• graphite in nodules not flakes
• matrix often pearlite - better
ductility
Chapter 11 - 8
Types of Cast Iron
White iron
• <1wt% Si so harder but brittle
• more cementite
Adapted from Fig. 11.3(c) & (d), Callister 7e.
Malleable iron
• heat treat at 800-900ºC
• graphite in rosettes
• more ductile
Chapter 11 - 9
Production of Cast Iron
Adapted from Fig.11.5,
Callister 7e.
Chapter 11 - 10
Limitations of Ferrous Alloys
1) Relatively high density
2) Relatively low conductivity
3) Poor corrosion resistance
Chapter 11 - 11
Nonferrous Alloys
• Cu Alloys
• Al Alloys
-lower r: 2.7g/cm3
Brass: Zn is subst. impurity
(costume jewelry, coins,
-Cu, Mg, Si, Mn, Zn additions
corrosion resistant)
-solid sol. or precip.
Bronze : Sn, Al, Si, Ni are
strengthened (struct.
subst. impurity
aircraft parts
(bushings, landing
& packaging)
gear)
• Mg Alloys
NonFerrous
Cu-Be:
-very low r: 1.7g/cm3
Alloys
precip. hardened
-ignites easily
for strength
-aircraft, missiles
• Ti Alloys
• Refractory metals
-lower r: 4.5g/cm3
vs 7.9 for steel
-reactive at high T
-space applic.
• Noble metals
-Ag, Au, Pt
-oxid./corr. resistant
Based on discussion and data provided in Section 11.3, Callister 7e.
-high melting T
-Nb, Mo, W, Ta
Chapter 11 - 12
Metal Fabrication
• How do we fabricate metals?
– Blacksmith - hammer (forged)
– Molding - cast
• Forming Operations
– Rough stock formed to final shape
Hot working
• T high enough for
recrystallization
• Larger deformations
vs.
Cold working
• well below Tm
• work hardening
• smaller deformations
Chapter 11 - 13
Metal Fabrication Methods - I
FORMING
CASTING
JOINING
• Forging (Hammering; Stamping) • Rolling (Hot or Cold Rolling)
(wrenches, crankshafts)
force
(I-beams, rails, sheet & plate)
roll
die
A o blank
A d often at
elev. T
• Drawing
force
Ao
Ad
roll
Adapted from
Fig. 11.8,
Callister 7e.
• Extrusion
(rods, wire, tubing)
die
Ao
Ad
(rods, tubing)
Ao
tensile
force
die
die must be well lubricated & clean
force
container
ram
billet
die holder
Ad
extrusion
die
ductile metals, e.g. Cu,
Al (hot)
Chapter 11 container
14
Metal Fabrication Methods - II
FORMING
CASTING
JOINING
• 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
Chapter 11 - 15
Metal Fabrication Methods - II
FORMING
CASTING
JOINING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
• trying to hold something that is hot
• what will withstand >1600ºC?
Sand
Sand
molten metal
• cheap - easy to mold => sand!!!
• pack sand around form (pattern) of
desired shape
Chapter 11 - 16
Metal Fabrication Methods - II
FORMING
CASTING
JOINING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
Investment Casting
• pattern is made from paraffin.
Sand
Sand
molten metal
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
plaster
die formed
around wax
prototype
• mold made by encasing in
plaster of paris
• melt the wax & the hollow mold
is left
• pour in metal
wax
Chapter 11 - 17
Metal Fabrication Methods - II
FORMING
CASTING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
Sand
• Die Casting
(high volume, low T alloys)
Sand
molten metal
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
plaster
die formed
around wax
prototype
JOINING
• Continuous Casting
(simple slab shapes)
molten
solidified
wax
Chapter 11 - 18
Metal Fabrication Methods - III
FORMING
CASTING
• Powder Metallurgy
(materials w/low ductility)
• Welding
(when one large part is
impractical)
pressure
filler metal (melted)
base metal (melted)
fused base metal
heat
area
contact
densify
JOINING
unaffected
piece 1
heat affected zone
unaffected
Adapted from Fig.
piece 2
11.9, Callister 7e.
• Heat affected zone:
point contact
at low T
densification
by diffusion at
higher T
(region in which the
microstructure has been
changed).
(Fig. 11.9 from Iron
Castings
Handbook, C.F.
Walton and T.J.
Opar (Ed.), 1981.)
Chapter 11 - 19
Thermal Processing of Metals
Annealing: Heat to Tanneal, then cool slowly.
• Stress Relief: Reduce
stress caused by:
-plastic deformation
-nonuniform cooling
-phase transform.
• Spheroidize (steels):
Make very soft steels for
good machining. Heat just
below TE & hold for
15-25 h.
Types of
Annealing
• Process Anneal:
Negate effect of
cold working by
(recovery/
recrystallization)
Based on discussion in Section 11.7, Callister 7e.
• Full Anneal (steels):
Make soft steels for
good forming by heating
to get g, then cool in
furnace to get coarse P.
• Normalize (steels):
Deform steel with large
grains, then normalize
to make grains small.
Chapter 11 - 20
Heat Treatments
800
a) Annealing
Austenite (stable)
T(°C)
TE
A
b) Quenching
P
600
c) Tempered
Martensite
B
A
400
Adapted from Fig. 10.22, Callister 7e.
0%
M+A
200
50%
M+A
90%
a)
b)
10
-1
10
10
time (s)
3
10
5
Chapter 11 - 21
c)
Hardenability--Steels
• Ability to form martensite
• Jominy end quench test to measure hardenability.
specimen
(heated to g
phase field)
24°C water
flat ground
Adapted from Fig. 11.11,
Callister 7e. (Fig. 11.11
adapted from A.G. Guy,
Essentials of Materials
Science, McGraw-Hill Book
Company, New York,
1978.)
Rockwell C
hardness tests
Hardness, HRC
• Hardness versus distance from the quenched end.
Adapted from Fig. 11.12,
Callister 7e.
Distance from quenched end
Chapter 11 - 22
Why Hardness Changes W/Position
Hardness, HRC
• The cooling rate varies with position.
60
40
20
0
1
2
3
distance from quenched end (in)
T(°C)
0%
100%
600
Adapted from Fig. 11.13, Callister 7e.
(Fig. 11.13 adapted from H. Boyer (Ed.)
Atlas of Isothermal Transformation and
Cooling Transformation Diagrams,
American Society for Metals, 1977, p.
376.)
400
200
M(start)
AM
0 M(finish)
0.1
1
10
100
1000
Time (s)
Chapter 11 - 23
Hardenability vs Alloy Composition
Adapted from Fig. 11.14, Callister 7e.
(Fig. 11.14 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.
100
Hardness, HRC
• Jominy end quench
results, C = 0.4 wt% C
10
3
60
2 Cooling rate (°C/s)
100
4340
80 %M
50
40
4140
8640
20
5140
0 10 20 30 40 50
Distance from quenched end (mm)
800
T(°C)
600
A
400
200
0 -1
10
10
B
TE
shift from
A to B due
to alloying
M(start)
M(90%)
103 105 Time (s)
Chapter 11 - 24
Quenching Medium & Geometry
• 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 increases
Position
center
surface
Cooling rate
low
high
Hardness
low
high
Chapter 11 - 25
Precipitation Hardening
• Particles impede dislocations.
700
• Ex: Al-Cu system
T(°C)
• Procedure:
600
--Pt A: solution heat treat
(get a solid solution)
--Pt B: quench to room temp.
--Pt C: reheat to nucleate
small q crystals within
a crystals.
• Other precipitation
systems:
• Cu-Be
• Cu-Sn
• Mg-Al
500
400
a
a+L
q+L
A
q
a+q
C
300
0 B 10
(Al)
CuAl2
L
20
30
40
50
wt% Cu
composition range
needed for precipitation hardening
Adapted from Fig. 11.24, Callister 7e. (Fig. 11.24 adapted from J.L.
Murray, International Metals Review 30, p.5, 1985.)
Temp.
Pt A (sol’n heat treat)
Pt C (precipitate q)
Adapted from Fig.
11.22, Callister 7e.
Pt B
Time
Chapter 11 - 26
Precipitate Effect on TS, %EL
• 2014 Al Alloy:
400
300
200
100
149°C
204°C
1min
1h 1day 1mo 1yr
precipitation heat treat time
• %EL reaches minimum
with precipitation time.
%EL (2 in sample)
tensile strength (MPa)
• TS peaks with
precipitation time.
• Increasing T accelerates
process.
30
20
10
0
204°C
149°C
1min
1h 1day 1mo 1yr
precipitation heat treat time
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 (Managing
Ed.), American Society for Metals, 1979. p. 41.)
Chapter 11 - 27
Metal Alloy Crystal Stucture
Alloys
• substitutional alloys
– can be ordered or disordered
– disordered solid solution
– ordered - periodic substitution
example: CuAu FCC
Cu
Au
Chapter 11 - 28
Metal Alloy Crystal Stucture
• Interstitial alloys (compounds)
– one metal much larger than the other
– smaller metal goes in ordered way into
interstitial “holes” in the structure of larger
metal
– Ex: Cementite – Fe3C
Chapter 11 - 29
Metal Alloy Crystal Stucture
• Consider FCC structure --- what types of
holes are there?
Octahedron - octahedral site = OH
Tetrahedron - tetrahedral site = TD
Chapter 11 - 30
Metal Alloy Crystal Stucture
• Interstitials such as H, N, B, C
• FCC has 4 atoms per unit cell
4 OH sites
8 TD sites
1
2
1
2
1
2
metal atoms
1
4,
3
4
1
4,
3
4
1
2
1
2
1
2
1
2
1
2
1
2
OH sites
1
4,
3
4
1
4,
3
4
TD sites
Chapter 11 - 31
Summary
• 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.
• Hardenability
--increases with alloy content.
• Precipitation hardening
--effective means to increase strength in
Al, Cu, and Mg alloys.
Chapter 11 - 32
ANNOUNCEMENTS
Reading:
Core Problems:
Self-help Problems:
Chapter 11 - 33