1. 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?

2. Taxonomy of Metals Steels Cast Irons <1.4 wt% C 3-4.5 wt% C
Alloys
Steels
Ferrous
Nonferrous
Cast Irons Cu Al Mg Ti
<1.4wt%C
3-4.5
wt%C
Steels
<1.4 wt% C
Cast Irons
3-4.5 wt% C
microstructure:
ferrite, graphite
cementite Fe 3 C
cementite
1600
1400
1200
1000
800
600
400 1 2 4 5 6
6.7 L g
austenite +L
+Fe3C a
ferrite +
L+Fe3C d
(Fe)
Co , wt% C
Eutectic:
Eutectoid:
0.76
4.30
727°C
1148°C
T(°C)

3. Ferrous alloy: iron is the prime constituent
Their widespread use is accounted for by three factors:
iron-containing compounds exist in abundant quantities within the earth’s crust;
metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques;
ferrous alloys are extremely versatile, they have a wide range of mechanical and physical properties
Disadvantage: their susceptibility to corrosion

4. Steels Low Alloy High Alloy low carbon <0.25 wt% C Med carbon
high carbon
wt% C
plain
HSLA
heat
treatable
tool
austenitic
stainless
Name
Additions
none
Cr,V
Ni, Mo
Cr, Ni Mo
Cr, V,
Mo, W
Cr, Ni, Mo
Example
1010
4310
1040 43 40
1095
4190
310
Hardenability + ++
+++ TS - + ++ EL + + - - -- ++
Uses
auto
bridges
crank
pistons
wear
drills
high T
struc.
towers
shafts
gears
applic.
saws
applic.
sheet
press.
bolts
wear
dies
turbines
vessels
hammers
applic.
furnaces
increasing strength, cost, decreasing ductility
blades
V. corros.
resistant

5. Low Alloy Plain carbon steels: contain only residual concentrations of
impurities other than carbon and a little manganese.
Alloy steels: more alloying elements are intentionally added in
specific concentrations ( Si, Cu, Al, V, Ni)
Low Alloy
Low carbon steel (<0.25 wt% C):
unresponsive to heat treatments
strengthening is accomplished by cold work
microstructures consist of ferrite and pearlite constituents
are relatively soft and weak
have outstanding ductility and toughness
they are machinable, weldable, and, of all steels, are the
least expensive to produce

6. Medium carbon steel (0.25-0.6 wt% C):
may be heat treated by austenitizing, quenching, and then
tempering to improve their mechanical properties
having microstructures of tempered martensite.
have low hardenabilities
additions of chromium, nickel, and molybdenum improve the
capacity of these alloys to be heat treated
stronger than the low-carbon steels, but at a sacrifice of ductility
and toughness
High carbon steel ( wt% C):
are the hardest, strongest, and yet least ductile of the carbon steels.
usually containing chromium, vanadium, tungsten, and molybdenum.

7. Stainless Steels
are highly resistant to corrosion (rusting) in a variety of environments
their predominant alloying element is chromium; a concentration of at
least 11 wt% Cr is required.
corrosion resistance may also be enhanced by nickel and molybdenum
additions
are divided into three classes—martensitic, ferritic, or austenitic
a wide range of mechanical properties
martensitic stainless steels are capable of being heat treated
used at elevated temperatures and in severe environments because they
resist oxidation and maintain their mechanical integrity under such
conditions
Equipment employing these steels includes gas turbines, high-
temperature steam boilers, heat-treating furnaces, aircraft, missiles, and
nuclear power generating units

8. Refinement of Steel from Ore
Iron Ore
Coke
Limestone
3CO +
Fe2O3
2Fe
+3CO2 C + O2
CO2
2CO
CaCO3
CaO+CO2
CaO + SiO2 + Al2O3
slag
purification
reduction of iron ore to metal
heat generation
Molten iron
BLAST FURNACE
air
layers of coke
and iron ore
gas
refractory
vessel

9. 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 ( %), Cr ( %), Mo ( %)
44xx Mo (0.5%)
where xx is wt% C x 100
example: steel – plain carbon steel with 0.60 wt% C
Stainless Steel -- >11% Cr
(SAE)The Society of Automotive Engineers
(AISI)The American Iron and Steel Institute
(ASTM)The American Society for Testing and Materials
(UNS) unified numbering system

10. Cast Iron Ferrous alloys with > 2.1 wt% C
more commonly wt%C
low melting (also brittle) so easiest to cast
Cementite (Fe3C ) is a metastable compound, and under some circumstances it can be dissociate or decomposes to form
ferrite + graphite
Fe3C  3 Fe () + C (graphite)
generally a slow process
So phase diagram for this system is different (Fig 12.4)

11. Fe-C True Equilibrium Diagram
1600
1400
1200
1000
800
600
400 1 2 3 4 90 L g +L
 + Graphite
Liquid +
Graphite
(Fe)
Co , wt% C
0.65
740°C
T(°C)
 + Graphite
100
1153°C
Austenite
4.2 wt% C
a + g
Graphite formation promoted by
Si > 1 wt%
slow cooling during solidification
Graphite is the carbon rich phase instead of cementite at 6.7 wt % C
for most cast iron the carbon exists as graphite
Cast irons have graphite

12. Types of Cast Iron Gray iron 2.5-4 wt% C, 1-3 wt% Si
graphite flakes(on ferrite matrix)
weak & brittle under tension
stronger under compression
excellent vibration dampening
wear resistant
The least expansive of all metallic materials
Ductile (nodular) iron
add Mg or Cerium (Ce)
graphite in nodules(sphere)not flakes
matrix often pearlite –
better ductility and stronger than gray

13. Types of Cast Iron White iron <1wt% Si and fast cooling
so harder but brittle
more cementite instead of graphite
is used as an intermediary in the
production of malleable iron.
Malleable iron
heat white at ºC for prolonged time
graphite in rosettes
relatively high strength and appreciable ductility or malleability

14. Compacted graphite iron ( CGI)
as gray, ductile, and malleable irons, carbon exists as graphite, which formation is promoted by the presence of silicon
1.7-3 wt % Si, wt% C
lower fracture and fatigue resistance of the materials, because
of presence of sharp edges ( characteristic of flaks graphite)
magnesium and/or cerium are added
Desirable characteristics of CGI include:
higher thermal conductivity
better resistance to thermal shock
lower oxidation at elevated temperatures
applications: diesel engine blocks, exhaust manifolds,
gearbox housing, flywheels

15. Gray cast iron
Ductile iron
Malleable iron
Connecting rod, transmission gear, pipe fittings
Diesel engine blocks, exhaust manifold, brake discs for high speed trains
Compacted iron

16. Production of Cast Iron

17. Limitations of Ferrous Alloys
Relatively high density
Relatively low conductivity
Poor corrosion resistance

18. Nonferrous Alloys
cast alloys: alloys that are so brittle that forming or shaping by appreciable deformation is not possible ordinarily are cast
wrought alloys: alloys that are amenable to mechanical deformation

19. Copper and its alloys: Unalloyed copper:
it is difficult to machine because its soft and ductile
it has an almost unlimited capacity to be cold worked
it is highly resistant to corrosion in diverse environments including
the ambient atmosphere, seawater, and some industrial chemicals.
high electrical and thermal conductivity
high ductility – EL 60%
melting temperature C, density 8.9 g/cm3

20. Copper alloys:
improved the mechanical and corrosion-resistance properties
most copper alloys cannot be hardened or strengthened by heat-
treating procedures
copper – zinc alloys (brasses)
- zinc up to 40%
- quite ductile and formable
- good corrosion resistance
copper – tin alloys (bronzes)
- more expensive because the high price of tin
- up to 20% Sn
- good strength, toughness, wear resistance, and corrosion resistance
coppers – beryllium alloys the most common precipitation hardenable
copper alloys. They possess a remarkable combination
of properties: tensile strengths as high as 1400 Mpa, excellent
electrical and corrosion properties, and wear resistance when properly
lubricated; they may be cast, hot worked, or cold worked. These alloys
are costly.

21. Aluminum and its alloys
high electrical and thermal conductivities
light weight , density 2.7 g/cm3
high resistance to corrosion in some common environments
are easily formed by virtue of high ductility;
limitation of aluminum is its low melting temperature 660 C
the mechanical strength of aluminum may be enhanced by cold
work and by alloying
alloying elements: copper, magnesium, silicon, manganese, zinc
A generation of new aluminum-lithium alloys
-- for use by the aircraft and aerospace industries
-- higher strength, greater stiffness, and lighter weight
-- materials have relatively low densities 2.5g/cm3
-- high specific moduli (elastic modulus-specific gravity ratios)
-- excellent fatigue and low-temperature toughness properties
-- costly to manufacture than the conventional aluminum alloys
-- are highly machinable, and can be welded

22. Magnesium and its alloys
the most outstanding characteristic is its density, 1.7 g/cm3
is relatively soft, and has a low elastic modulus
at room temperature magnesium and its alloys are difficult to deform
most fabrication is by casting or hot working
has a moderately low melting temperature 651C
fine magnesium powder ignites easily when heated in air
aluminum, zinc, manganese, and some of the rare earths are the
major alloying elements
Titanium and its alloys
the pure metal has a relatively low density(4.5 g/cm3), a high melting point 1668C and an elastic modulus of 107GPa
titanium alloys are extremely strong; room temperature tensile strengths as high as 1400 Mpa are attainable, yielding remarkable
specific strengths. Furthermore, the alloys are highly ductile and easily forged and machined
the major limitation of titanium is its chemical reactivity with other materials at elevated temperatures, high costs, fabrication difficult

23. The Refractory metals
metals that have extremely high melting temperatures
included in this group are niobium (Nb 2470C), molybdenum
(Mo 2610), tungsten(W 3410), and tantalum (Ta 3000)
melting temperatures range between 2470 C for niobium and 3410C
the highest melting temperature of any metal, for tungsten
applications: tantalum and molybdenum are alloyed with stainless
steel to improve its corrosion resistance. Molybdenum alloys are
utilized for extrusion dies and structural parts in space vehicles;
incandescent light filaments x-ray tubes, and welding electrodes
employ tungsten alloys.

24. The super alloys have superlative combinations of properties
most are used in aircraft turbine components, which must withstand
exposure to severely oxidizing environments and high temperatures
for reasonable time periods
density is an important consideration
these materials are classified according to the predominant metal in
the alloy, which may be cobalt, nickel, or iron.( g/cm3 )
applications: jet engine, gas turbine, rocket, nuclear reactors
and petrochemical equipment. They posses high strength, creep
resistance, and corrosion resistance at temperature up to and in
excess of 1100 C
are difficult to machine. Powder metallurgy techniques are also
being used extensively in the manufacturing of super alloy
components

25. The Noble metals Nickel and its alloys
the noble or precious metals are a group of eight elements that
have some physical characteristics in common
they are expensive
are superior or notable (noble) in properties
characteristically soft, ductile, and oxidation resistant
silver, gold, platinum, palladium, rhodium, ruthenium, iridium,
and osmium
Nickel and its alloys
are highly resistant to corrosion in many environments(alkaline),
salt water, high-velocity, high-temperature steam
nickel is often coated or plated on some metals that are susceptible
to corrosion as a protective measure
nickel is one of the principal alloying elements in stainless steels,
and one of the major constituents in the superalloy
applications: pumps, valves, steam turbine blades

26. Nonferrous Alloys NonFerrous Alloys • Cu Alloys • Al Alloys
Brass: Zn is subst. impurity
(costume jewelry, coins,
corrosion resistant)35% Zn
Bronze
: Sn, Al, Si, Ni are
subst. impurity
(bushings, landing
gear)
Cu-Be :
precip. hardened
for strength
• Al Alloys
-lower r
: 2.7g/cm3
-Cu, Mg, Si, Mn, Zn additions
-solid sol. or precip.
strengthened (struct.
aircraft parts
& packaging)
• Ti Alloys
-lower r
: 4.5g/cm3
7.9 for steel
-reactive at high T -
space application.
NonFerrous
Alloys
• 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

27. Metal Fabrication How do we fabricate metals?
Blacksmith - hammer (forged)
Molding - cast
Forming Operations
Rough stock formed to final shape
Hot working vs Cold working
• T high enough for • well below Tm recrystallization • work hardening
• Larger deformations • smaller deformations
Material loss increase strength
Poor final surface finish higher quality surface
-- better mechanical properties
-- closer dimensional control

28. Metal Fabrication Methods
FORMING
CASTING
JOINING
Forming: Forming operations are those in which the shape of a metal piece is changed by plastic deformation; the deformation must be induced by an external force or stress, the magnitude of which must exceed the yield strength of the material. Most metallic materials are especially amenable to these procedures, being at least moderately ductile and capable of some permanent deformation without cracking or fracturing.
hot working: When deformation is achieved at a temperature above that at which recrystallization occurs. otherwise, it is
cold working. With most of the forming techniques, both hot- and cold-working procedures are possible.

29. Joining: powder metallurgy and welding
Casting: Casting is a fabrication process whereby a totally molten metal is poured into a mold cavity having the desired shape; upon solidification, the metal assumes the shape of the mold but experiences some shrinkage.
Casting techniques are employed when
the finished shape is so large or complicated that any other method would be impractical,
a particular alloy is so low in ductility that forming by either hot or cold working would be difficult, and
(3) in comparison to other fabrication processes, casting is the most
economical
Joining: powder metallurgy and welding

30. Metal Fabrication Methods - I
FORMING
CASTING
JOINING A o d
force
die
blank
• Forging (Hammering; Stamping)
(wrenches, crankshafts)
often at
elev. T
roll A o d
• Rolling (Hot or Cold Rolling)
(I-beams, rails, sheet & plate)
tensile
force A o d
die
• Drawing
(rods, wire, tubing)
die must be well lubricated & clean
ram
billet
container
force
die holder
die A o d
extrusion
• Extrusion
(rods, tubing)
ductile metals, e.g. Cu, Al (hot)

31. Forging is mechanically working or deforming a single piece of a normally hot metal; this may be accomplished by the application of successive blows or by continuous squeezing. Forgings are classified as either closed or open die.
Rolling is the most widely used deformation process, consists of passing a piece of metal between two rolls; a reduction in thickness results from compressive stresses exerted by the rolls. Cold rolling may be used.
Extrusion a bar of metal is forced through a die orifice by a compressive force that is applied to a ram; the extruded piece that emerges has the desired shape and a reduced cross-sectional area.
Drawing is the pulling of a metal piece through a die having a tapered bore by means of a tensile force that is applied on the exit side. A reduction in cross section results, with a corresponding increase in length. The total drawing operation may consist of a number of dies in a series sequence.

32. 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

33. 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?
cheap - easy to mold => sand!!!
pack sand around form (pattern) of desired shape
Sand
molten metal

34. Metal Fabrication Methods - II
FORMING
CASTING
JOINING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
Investment Casting
pattern is made from paraffin.
mold made by encasing in plaster of paris
melt the wax & the hollow mold is left
pour in metal
Sand
molten metal
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
plaster
die formed
around wax
prototype
wax

35. Metal Fabrication Methods - II
FORMING
CASTING
JOINING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
• Die Casting
(high volume, low T alloys)
Sand
molten metal
• Continuous Casting
(simple slab shapes)
molten
solidified
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
plaster
die formed
around wax
prototype
wax

36. Metal Fabrication Methods - III
FORMING
CASTING
JOINING
• Powder Metallurgy
(materials w/low ductility)
• Welding
(when one large part is
impractical)
• Heat affected zone:
(region in which the
microstructure has been
changed).
piece 1
piece 2
fused base metal
filler metal (melted)
base
metal (melted)
unaffected
heat affected zone
pressure
heat
point contact
at low T
densification
by diffusion at
higher T
area
contact
density

37. Powder metallurgy: the compaction of powdered metal, followed by a heat treatment to produce a more dense piece. Powder metallurgy makes it possible to produce a virtually nonporous piece having properties almost equivalent to the fully dense parent material. Diffusional processes during the heat treatment are central to the development of these properties. suitable for metals having low ductilities.
Welding: two or more metal parts are joined to form a single piece when one-part fabrication is expensive or inconvenient. Both similar and dissimilar metals may be welded.

38. Thermal Processing of Metals
Annealing: a heat treatment in which a material is exposed to an elevated temperature for an extended time period and then slowly cooled. Is used to negate the effects of cold work, that is, to soften and increase the ductility of a previously strain-hardened metal. It is commonly utilized during fabrication procedures that require extensive plastic deformation
relieve stresses;
increase softness, ductility, and toughness;
produce a specific microstructure.
Three steps:
heating to the desired temperature,
holding or ‘‘soaking’’ at that temperature, and
cooling, usually to room temperature

39. Annealing of ferrous alloys:
Normalizing
Full annealing
Spheroidizing
Heat treatment of steels:
quenching
tempering
The successful heat treating of steels to produce a predominantly martensitic microstructure throughout the cross section depends mainly on three factors:
(1) the composition of the alloy,
(2) the type and character of the quenching medium, and
(3) the size and shape of the specimen.

40. Thermal Processing of Metals
Annealing: Heat to Tanneal, then cool slowly.
Types of
Annealing •
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. •
Full Anneal
(steels):
Make soft steels for
good forming by heating
to get g
, then cool in
furnace to get coarse P. •
Process Anneal:
Negate effect of
cold working by
(recovery/
recrystallization) •
Normalize
(steels):
Deform steel with large
grains, then normalize
to make grains small.

41. Heat Treatments Annealing Quenching Tempered Martensite a) b) c) TE
800
Austenite (stable) a) b)
Annealing TE
T(°C) A
Quenching P
600
Tempered Martensite B
400 A
100%
50% 0% c) 0%
200
M + A
50%
M + A
90% -1 3 5 10 10 10 10
time (s)

42. Hardenability--Steels
• Ability to form martensite
• Jominy end quench test to measure hardenability.
24°C water
specimen
(heated to g
phase field)
flat ground
Rockwell C hardness tests
• Hardness versus distance from the quenched end.
Hardness, HRC
Distance from quenched end

43. Why Hardness Changes W/Position
• The cooling rate varies with position. 60
Martensite
Martensite + Pearlite
Fine Pearlite
Pearlite
Hardness, HRC 40 20
distance from quenched end (in) 1 2 3
600
400
200 A M P
0.1 1 10
100
1000
T(°C)
M(start)
Time (s) 0%
100%
M(finish)

44. Hardenability vs Alloy Composition
Cooling rate (°C/s)
Hardness, HRC 20 40 60 10 30 50
Distance from quenched end (mm) 2
100 3
4140
8640
5140
1040 80 %M
4340
• Jominy end quench
results, C = 0.4 wt% 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.
T(°C) 10 -1 3 5
200
400
600
800
Time (s)
M(start)
M(90%)
shift from
A to B due
to alloying B A TE

45. 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

46. Precipitation Hardening
• Particles impede dislocations.
• Ex: Al-Cu system
• Procedure: 10 20 30 40 50
wt% Cu L
+L a
a+q q
+L
300
400
500
600
700
(Al)
T(°C)
composition range
needed for precipitation hardening
CuAl2 A
--Pt A: solution heat treat (get a solid solution) B
Pt B
--Pt B: quench to room temp. C
--Pt C: reheat to nucleate small q crystals within a crystals.
Other precipitation systems: • Cu-Be • Cu-Sn • Mg-Al
Temp.
Time
Pt A (sol’n heat treat)
Pt C (precipitate )

47. Precipitate Effect on TS, %EL
• 2014 Al Alloy:
• TS peaks with
precipitation time.
• Increasing T accelerates
process.
• %EL reaches minimum
with precipitation time.
%EL (2 in sample) 10 20 30
1min 1h
1day
1mo
1yr
204°C
149 °C
precipitation heat treat time
precipitation heat treat time
tensile strength (MPa)
200
300
400
100
1min 1h
1day
1mo
1yr
204°C
non-equil.
solid solution
many small
precipitates
“aged”
fewer large
“overaged”
149°C

48. Metal Alloy Crystal Stucture
Alloys
substitutional alloys
can be ordered or disordered
disordered solid solution
ordered - periodic substitution
example: CuAu FCC Cu Au

49. 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

50. Metal Alloy Crystal Stucture
Consider FCC structure what types of holes are there?
Octahedron - octahedral site = OH
Tetrahedron - tetrahedral site = TD

51. Metal Alloy Crystal Stucture
Interstitials such as H, N, B, C
FCC has 4 atoms per unit cell
OH sites
4 OH sites
TD sites
8 TD sites
metal atoms

52. 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.