Chapters 11 (Part II)

Metal Alloys

•

Part I:

Thermal Processing of Metal

Alloys

–

Heat Treatment

–

Precipitation Hardening

•

Part II:

Metal Alloys and Fabrication of

Metals

Outline of Chapter 11

•

Ferrous Alloys: Alloys containing more than 50wt.%Fe

–

Classification of Steels

–

Designation of Steels

•

Nonferrous Alloys: Alloys containing less than 50wt.

%Fe

–

Aluminum

–

Copper

–

Magnesium

–

Titanium

–

Refractory metals

–

Superalloys

–

Noble metals

Metal Alloys

Metal Alloys

Ferrous

Nonferrous

Steels

Cast Irons

Low Alloy

Low-carbon Medium-

carbon

High-

carbon

High Alloy

Plai

n

High

strengt

h, low

alloy

Heat

treatab

le

Plai

n

Tool

Plai

n

Stainles
s

Gra

y

iron

Whit

e

iron

Malleabl

e iron

Ductil

e iron

Classification of Ferrous

Alloys

–

Steels

(0.008 ~ 2.14wt% C)

In most steels the microstructure consists of both  and

Fe

3

C phases.

Carbon concentrations in commercial steels rarely

exceed 1.0 wt%.

–

Cast irons

(2.14 ~ 6.70wt% C)

Commercial cast irons normally contain less than 4.5wt
% C

Classification of Ferrous

Alloys

•

Based on carbon

content

–

Pure iron

(<

0.008wt% C)
From the phase

diagram, it is

composed almost

exclusively of the

ferrite phase at room

temperature.

•

The carbon content is normally less than
1.0 wt%.

•

Plain carbon steels:

containing only

residual concentrations of impurities other
than carbon and a little manganese

About 90% of all steel made is carbon steel.

•

Alloy steels:

more alloying elements are

intentionally added in specific
concentrations.

•

Stainless steels

Ferrous Alloys — Steels

•

Low-carbon steels

–

Less than 0.25 wt%C

•

Medium-carbon steels

–

0.25 ~ 0.60 wt%C

•

High-carbon steels

–

0.60 ~ 1.4 wt%C

Classification of Steels

According to Their Carbon Contents

•

A

four-digit number:

–

the first two digits indicate the alloy
content;

–

the last two, the carbon concentration

•

For plain carbon steels, the first two digits
are 1 and 0;

alloy steels are designated by

other initial two-digit combinations (e.g., 13,
41, 43)

•

The third and fourth digits represent the
weight percent carbon multiplied by 100

For example, a 1040 steel is a plain carbon
steel containing 0.40 wt% C.

The Designation of Steels

•

A

four-digit number

: the first two digits

indicate the alloy content; the last two,
the carbon concentration

41

41

40

40

Identifies
major
alloying
element(s)

Percentag
e of
carbon

The Designation of Steels

•

AISI:

A

merican

I

ron and

S

teel

I

nstitute

•

SAE:

S

ociety of

A

utomotive

E

ngineers

•

UNS:

U

niform

N

umbering

S

ystem

Table 11.2a AISI/SAE and UNS Designation

Systems

Steel Alloys

Steel Numerical Name

Key Alloys

10XX, 11 XX

Carbon only

13XX

Manganese

23XX, 25 XX

Nickel

31XX, 33XX, 303XX

Nickel-Chromium

40XX

Mo

41XX

Cr-Mo

43XX & 47XX

Ni-Cr-Mo

44XX

Mn-Mo

48XX

Ni-Mo

50XX, 51XX, 501XX, 521XX,

514XX, 515XX

Cr

61XX

Cr-V

81XX, 86XX, 87XX, 88XX

Ni-Cr-Mo

92XX

Si-Mn

93XX, 98XX

Ni-Cr-Mo

94XX

Ni-Cr-Mo-Mn

XXBXX

Boron

XXLXX

Lead

94XX Ni-

•

Less than 0.25 wt%C

•

Unresponsive to heat treatments intended to
form martensite;

strengthening is

accomplished by cold work

•

Microstructures:

ferrite and pearlite

•

Relatively soft and weak, but having
outstanding ductility and toughness

•

Typically, 

y

= 275 MPa, 

UT

= 415~550 MPa,

and ductility = 25%EL

•

Machinable, weldable, and, of all steels, are
the least expensive to produce

•

Applications:

automobile body components,

structural shapes, and sheets used in
pipelines, buildings, bridges, etc.

Low-Carbon Steels

TTT Diagram of Some Hypoeutectoid

Alloys

Table 11.1a

Compositions of Five Plain Low-Carbon

Steels

Table 11.1b

Mechanical Characteristics of Hot-Rolled Material

and Typical Applications for Various Plain Low-

Carbon Steels

•

0.25 ~ 0.60 wt%C

•

May be

heat treated

by austenitizing,

quenching, and then tempering to improve
their mechanical properties

•

Stronger than low-carbon steels and weaker
than high-carbon steels

a

Classified as high-carbon steels

Typical Tensile Properties for Oil-Quenched and Tempered Plain

Carbon

Medium-Carbon Steels

•

0.60 ~ 1.4 wt%C

•

Used in a

hardened and tempered

condition

•

Hardest, strongest, and yet least ductile;
especially wear resistant and capable of
holding a sharp cutting edge

•

Containing Cr, V, W, and Mo; these alloying
elements combine with carbon to form very
hard and wear-resistant carbide compounds
(e.g., Cr

23

C

6

, V

4

C

3

, and WC)

•

Applications:

cutting tools and dies for

forming and shaping materials, knives,
razors, hacksaw blades, springs, and high-
strength wire

High-Carbon Steels

Table 11.3 Designations, Compositions,

and Applications for Six Tool Steels

Carbon Steel

Alloy Steel

Lower cost

Higher strength

Greater availability

Better wear

Toughness

Special high temperature

behavior

Better corrosion

resistance

Special electrical

properties

94XX Ni-

•

Alloy steel is more expensive than carbon steel; it should
be used only when a special property is needed.

Comparison of the Advantages

Offered by Carbon Steels and Alloy

Steels

Table 11.2a AISI/SAE and UNS Designation

Systems

What makes stainless steels

“stainless”?

•

Stainless steels are selected for their
excellent resistance to corrosion.

•

Stainless steels are divided into three
classes: martensitic, ferritic, or austenitic

•

The predominant alloying element is

chromium

; a concentration of at least 11 wt%

Cr is required

–

It permits a thin, protective surface layer
of chromium oxide to form when the steel
is exposed to oxygen.

–

The chromium is what makes stainless
steel stainless!

Stainless Steels

•

Aluminum and aluminum alloys are the most widely
used nonferrous metals.

•

Aluminum alloys:

strengthened by cold working and

alloying (Cu, Mg, Si, Mn, and Zn)

–

Nonheat-treatable: single phase, solid solution strengthening

–

Heat treatable: precipitation hardening (MgZn

2

)

•

Properties

–

Low density (2.7 g/cm

3

), as compared to 7.9 g/cm

3

for steel

–

High electrical and thermal conductivity

–

Resistant to corrosion in some common environments

–

Easily formed and thin Al foil sheet may be rolled

–

Al has an FCC crystal structure; its ductility is retained even
at very low temperatures

–

Limitation: low melting temperature (660°C)

Aluminum and Its Alloys

Aluminum Alloy Desginations

Material

Number

Al (99.00% minimum and

greater)

1XXX

Al alloys are grouped by

major alloying elements

Copper

2XXX

Manganese

3XXX

Silicon

4XXX

Magnesium

5XXX

Magnesium and Silicon

6XXX

94XX Ni-

Aluminum’s use in vehicles is rapidly increasing

due to

the need for fuel efficient, environmentally friendly

vehicles

•

Al alloys can provide a
weight savings of up to
55% compared to an
equivalent steel
structure

•

It can match or exceed
crashworthiness
standards of similarly
sized steel structures

•

The Ford Motor
Company now has
aluminum-intensive test
vehicles on the road,
providing 46% weight
savings in the structure,
with no loss in crash
protection.

Aluminum plate is used in the

manufacture of aircraft and for fuel

tanks in spacecraft

•

Aircraft manufacturers use high-strength alloys

(principally alloy 7075)

to strengthen aluminum

aircraft structures.

•

Alloy 7075 has

zinc and copper

added for ultimate

strength, but because of the copper it is very
difficult to weld.

•

7075 has the best machinability and results in the
finest finish.

Lightweight aluminum is a

good material for conductor

cables

•

Electrical transmission
lines are the largest
users of aluminum
rod/bar/wire products.

•

In fact, this is the one
market in which
aluminum has virtually
no competition from
other metals.

•

Aluminum is simply
the most economical
way to deliver
electrical power.

•

Unalloyed copper:

–

So soft and ductile that it is difficult to machine

–

Unlimited capacity to be cold worked

–

Highly resistant to corrosion in diverse
environments

•

Copper alloys:

strengthened by cold working

and/or solid-solution alloying.

•

Bronze and brass

are two common copper alloys.

•

Applications:

costume jewelry, cartridge casings,

automotive radiators, musical instruments,
electronic packaging, and coins

Copper and Its Alloys

•

Bronze

is an alloy of

copper and tin

.

–

The first metal

purposely alloyed

by the smith

–

May contain up to

25% tin

•

Brass

is an alloy of

copper

and zinc

.

–

Contain 5-30% zinc

–

The zinc increases the strength of the

copper.

–

Ductility and formability are also

increased.

Bronz

e

Mask

Bronze and Brass

Brass — An Alloy of Copper and Zinc

Fig. 9.17

The copper-zinc phase

diagram.

•

Relatively new engineering materials that
possess an extraordinary combination of
properties

–

Low density (4.5 g/cm

3

)

–

High melting temperature (1668°C), high elastic
modulus (107 GPa)

–

Extremely strong: 1400 MPa tensile strength at
room temperature, highly ductile and easily
forged and machined

–

Limitations



Chemical reactivity with other materials and
oxidation problem at elevated temperatures



Cost

•

Applications:

airplane structures, space vehicles,

and in the petroleum and chemical industries

Titanium and Its Alloys

Alloy

Type

Common

Name

(UNS

Numbser)

Composition

(wt%)

Condition

Tensile

Strength

(MPa)

Yield

Strength

(MPa)

Ductility

(%EL)

  Ti-6Al-4V

(R564000)

6Al, 4V,

balance Ti Annealed

947

877

14

94XX Ni-

•

Typical Applications:

High-strength prosthetic

implants, chemical-processing equipment,
airframe structural components

An Example of Titanium Alloy (Table

11.9)

•

Superlative combinations of

properties

–

Nickel-based alloys

–

Other alloying elements: Nb, Mo,

W, Ta, Cr, and Ti
IN792: Ni-12Cr-10Co-2Mo-4W-

3.5Al-4Ti-4Ta- 0.01B-0.09Zr-

0.1C-0.5Hf

•

Applications:

aircraft turbine

components

–

Turbine blades and discs, high

creep and oxidation resistance

at elevated temperatures

(1000°C)

–

Density

is an important

consideration because

centrifugal stresses are

diminished in rotating parts

when the density is reduced

Ni-Base Superalloys

Titanium Alloy

Steel

Aluminum Alloy

Nickel Alloy

Material Strength with Increased

Temperature

•

Modern aeroengine design constantly seeks to increase
the engine operating temperature to improve overall
efficiency.

•

Materials for turbine blades are required to perform at
higher and higher temperatures.

•

Use of advanced nickel-based alloys, together with
innovative cooling design

Ni-Based Superalloys Used for Turbine

Blades

Polycrystalli
ne turbine
blade

Improvement in Creep Resistance of

Turbine Blades through Casting

Technologies

Columnar grain
structure produced
by a directional
solidification
technique

Creep resistance
is further
enhanced with
single-crystal
blades.

Thermal Barrier Coatings (TBCs)

•

Demands for higher efficiency and lower emission require

higher operating temperatures

in aeroengines

•

The typical melting points of the superalloys used for the
turbine components range from 1230-1315°C

•

The temp. in a combustion gas environment is > 1370°C

Thermally Grown

Oxide (TGO)

(1-10m)

Ceramic Top Coat (100-400m)

(Y

2

O

3

-Stabilized ZrO

2

)

Bond Coat (~100m)

Substrate

Cooling Air

Hot Gases

Thermally Grown

Oxide (TGO)

(1-10m)

Ceramic Top Coat (100-400m)

(Y

2

O

3

-Stabilized ZrO

2

)

Bond Coat (~100m)

Substrate

Cooling Air

Hot Gases

The key to meeting
the higher
temperature
requirements lies in
providing an
insulating ceramic

thermal barrier
coating (TBC)

to

lower the surface
temperature of
superalloy
underneath

•

Melting temperatures range between 2468°C for
niobium (Nb) and 3410°C for tungsten (W)

–

Interatomic bonding is extremely strong.

–

Large elastic moduli and high strength and
hardness at ambient and elevated
temperatures

•

Applications:

–

Ta and Mo are alloyed with stainless steel to
improve its corrosion resistance.

–

Molybdenum alloys: extrusion dies and
structural parts in space vehicles

–

Tungsten alloys: filaments, X-ray tubes,
welding electrodes

Refractory Metals

It is necessary to select a steel alloy for a gearbox
output shaft. The design calls for a 1-in diameter
cylindrical shaft having a surface hardness of at
least 38 HRC and a minimum ductility of 12%EL.

Specify an alloy and treatment that meet these
criteria.

Design Example 11.1

•

To select a steel alloy for a gearbox output shaft,

a 1-in diameter cylindrical shaft.

–

Surface hardness  38 HRC

–

Ductility >12%EL

•

Specify an alloy and treatment that meet these

criteria

•

Cost is always an important design consideration.

–

This would eliminate relatively expensive

steels, such as stainless steels.

–

Examine

plain-carbon and low-alloy steels

, and

what treatments are available to alter their

mechanical properties.

•

Two approaches

–

Cold work

–

Heat treatment  martensite

Design Example 11.1

Relationships between Hardness and

Tensile Strength for Steel, Brass, and

Cast Iron

Adapted from Fig.
6.19, Callister 6e.

Fig. 7.17

For 1040 steel, brass, and copper, (b) the increase

in tensile strength, and (c) the decrease in ductility (%EL)
with percent cold work

The Correlation between Cold Work and

Tensile Strength and Ductility for Various

Alloys

Design Example 11.1

•

1-in diameter cylindrical shaft.

•

Having a surface hardness of at least 38 HRC
and a minimum ductility of 12%EL

•

Cold work

–

From Fig. 6.19, a hardness of 38 HRC
corresponds to a tensile strength of 1200
MPa

.

–

From Fig. 7.17(b), at 50% cold work, a
tensile strength is only ~900 MPa and
the ductility is ~10%EL.

–

Both of these properties fall short of
those specified in the design.

•

Cold working other plain-carbon or low-alloy steels

would probably not achieve the required minimum

values.

•

To perform a series of heat treatments in which the

steel is austenitized, quenched (to form martensite),

and finally tempered.

–

Examine the mechanical properties of various

plain-carbon and low-alloy steels that have been

treated in this manner.

–

The surface hardness of the quenched material will

depend on both alloy content and shaft diameter.

Design Example 11.1

Table 11.10

Surface hardnesses for oil-quenched cylinders of

1060 steel having various diameters.

Design Example 11.1

Table 11.11

Rockwell hardness (surface) and percent

elongation values for 1-in. diameter cylinders of six steel
alloys, in the as-quenched condition and for various tempering
heat treatments.

•

The only alloy-heat treatment combinations that meet the

stipulated criteria are 4150/oil-540°C temper, 4340/oil-540°C

temper, and 6150/oil-540°C temper.

•

The costs of these three materials are probably comparable.

•

The 6150 alloy has the highest ductility (by a narrow

margin), which would give it a slight edge in the selection

process.

Steel Alloys

Steel Numerical Name

Key Alloys

10XX, 11 XX

Carbon only

13XX

Manganese

23XX, 25 XX

Nickel

31XX, 33XX, 303XX

Nickel-Chromium

40XX

Mo

41XX

Cr-Mo

43XX

& 47XX

Ni-Cr-Mo

44XX

Mn-Mo

48XX

Ni-Mo

50XX, 51XX, 501XX,

521XX, 514XX, 515XX

Cr

61XX

Cr-V

81XX, 86XX, 87XX, 88XX

Ni-Cr-Mo

92XX

Si-Mn

93XX, 98XX

Ni-Cr-Mo

94XX

Ni-Cr-Mo-Mn

94XX Ni-

Steel Alloys

Alloying

Element

4150

4340

6150

C

0.48-0.53

0.38-0.43

0.48-0.53

Mn

0.75-1.00

0.60-0.80

0.70-0.90

P

0.035

0.035

0.035

S

0.040

0.040

0.040

Si

0.15-0.35

0.15-0.35

0.15-0.35

Ni

--

1.65-2.00

--

Cr

0.80-1.10

0.70-0.90

0.80-1.10

Mo

0.15-0.25

0.20-0.30

--

V

--

--

0.15 min

94X X Ni-