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Technology

of of

Metallic Materials

Prof. G. Ubertalli

Text-book:

- Lecture notes - Prof. Graziano Ubertalli (portale della didattica)

Main topics

Introduction

Hardening mechanism

Aluminium, magnesium, titanium, copper alloys Aluminium, magnesium, titanium, copper alloys

Steels and cast irons

Corrosion and prevention

Heat treatments

Technological tests, microscopy

Laboratory

Prof. G. Ubertalli

Laboratory

Intermediate test

Final test

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Introduction of ... Metallic Materials

Metallic bonds

High plastic strain

Hardened after work hardening

The main alloys are ductile

They are composite metallic materials

Prof. G. Ubertalli

They show a wide range of chemical,

physical and technological properties.

Lattice StructuresFace Cubic Centered Iron (907-1400 C)

Copper

Silver

Gold

Nickel

Aluminium

LeadLead

Platinum

Body Cubic Centered Iron (< 907 C, > 1400 C)

Tungsten

Vanadium

Molybdenum

Chromium

Alcaline Metals (Na, K)

Prof. G. Ubertalli

Compact Hexagonal Zinc

Magnesium

Titanium

Zirconium

Beryllium

Cadmium

Cobalt

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Cubic Lattice

BCC BCC

Prof. G. Ubertalli

FCC

Hexagonal lattice

HEX, HCP HEX, HCP

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Comparison FCC - HEXC

Prof. G. Ubertalli

Main ordered structures

AuCu

Cu

Au3Cu

Cu

Some examples of ordered

Cu

Au

Cu

Au

CuZn

Cu

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Some examples of ordered

structure that respect the

stoichiometry formula.

Cu

Zn

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Bond Energy

ELegame forteStrong bond

Strong bond

Legame forte

Legame debole

Strong bond

Weak bond

Weak bond

Prof. G. Ubertalli

a

Thermal expansion coefficient

Coefficienti di dilatazione termica a 20 C

70

80

Hg

PbAl

CuFe

W

CsCl

NaCl

MgO

0

10

20

30

40

50

60

70

-100 900 1900 2900

Temperatura di fusione (C)

Coeff(*10E-6)

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Influence of lattice structure and bond energy

(melting temperature) on the thermal expansion

coefficient.

Temperatura di fusione (C)

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Bond Energy - Physical characteristics

Poisson Modulus

Elastic Modulus

E (GPa)

Melting Temperature

(C)

Lattice

W 0,27 350 3410 CCC

Fe 0,28 210 1537 CCC

Cu 0,35 112 1083 CFC

Al 0,34 70 660 CFC

Mg 42 650 EXC

Pb 0,4 15,4 327 CFC

Prof. G. Ubertalli

The greater the energy bond, the higher the elastic

modulus and the higher the melting temperature.

Crystallography

In an ordered lattice there are preferred directions

and planes that connect atomic sites. Atoms can be

represented as rigid spheres in contact with each

other. These are high packed directions and planes.

In the BCC lattice the spheres touch each other in

the direction of the main diagonals of the cube. In

the FCC lattice this happens on the diagonals of the

faces.

Prof. G. Ubertalli

faces.

Along these high packed directions, plastic slip

may take place.

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Hardening mechanism

Grains size

Solid solution Solid solution

Strain hardening

Precipitation of a second phase

Alloy #ot reinforced

[MPa]

Reinforced

[MPa]

Maximum

[MPa]

Prof. G. Ubertalli

[MPa] [MPa] [MPa]

Iron 100 900 3000

Alluminium 50 350-450 700

Copper 55 600 1350

Lattice defects

There are different types of lattice defects:

Punctual vacancies

Prof. G. Ubertalli

Punctual vacancies

Linear dislocations

Plain grains boundaries

Volume stacking faults

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VacanciesA two-dimensional representation of

a vacancy in an ordered lattice.

The amount of vacancies depends on

the temperature of the alloy in

respect to its melting temperature.

nv

n0= e

W vKT

Prof. G. Ubertalli

Vacancies justify the motion of

chemical elements in the lattice. D= D0e

Q

RT

Dislocations

A two-dimensional

representation of an edge

dislocation.

1 2 3 4

5 6 7

dislocation.

A three-dimensional

representation of an edge

dislocation.

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A TEM image of screw

dislocations near second

phase particles.

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Schmidt's law - (max.)A law used to derive the maximum

shear stress .

As is a generic surface obtained by

cutting a cylinder under an angle Pwith respect to the surface A,

perpendicular to the applied load.

We can write:

AS = A / cos The tangential stress which works onthe inclined area AS is:

= P / AS cos Substituting:

As

N

Prof. G. Ubertalli

Substituting:

= P/A cos cos

This equation evidences that the

maxima shear stresses are obtained

for and values of: = (90-) = 45

Which gives: = 0,5P/A .

P

Dislocations

The slipping of a

complete complete

crystallographic

plane in a perfect

lattice could bring

about very high

tangential stresses.0,5

0,75

1

Prof. G. Ubertalli

tangential stresses.

0 1 2 3 4 5 6 7

-1

-0,75

-0,5

-0,25

0

0,25

0,5

Pi greco

Energia

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Dislocations

If we take a glance at

the two images on the

right they may seen

1 2 3 4

5 6 7

right they may seen

equal ....

.... but be careful!

Prof. G. Ubertalli

.... but be careful!

A dislocation motion

has taken place!

1 2 3 4

5 6 7

Grains

Petchs law.

= + kD(-1/2)

O ttone rico tto 70-30

50

60

70

Resistenza a trazione [psi]

Allungamento %

0 ,01 0,05 0,002 0 ,001

| | | |

0 = i + kD(-1/2)

Prof. G. Ubertalli

20

30

40

0 1000 2000 3000

A re a d e i b o rd i g ra n o [cm ^ 2 /cm ^ 3 ]

Resistenza a trazione [psi]

Allungamento %

Resistenza

Allungamento

Grain size reticle

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Grains IGrain size

(average) [m]Average Area

[m2]Number of

grains in 1 mm2Grains per

square inches at100 X

A.S.T.M. Number

280 62.000 16 1 1200 31.000 32 2 2200 31.000 32 2 2140 15.600 64 4 3100 7.800 128 8 470 3.900 256 16 550 1.950 512 32 635 980 1024 64 725 490 2048 128 8

N = 2(n-1)

Prof. G. Ubertalli

N = 2

where:N Grains per square inches

n A.S.T.M. NumberCast iron

Grains II

Fine grains

Ma

xim

um

str

en

gth

Transgranular Intergranular

Fine grains

Coarse grains

Fracture mechanism as a function of the test temperature

Prof. G. Ubertalli

Te T [C]

Transgranular Intergranular

Grains size and deformability ..

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Grains IIIExample

A steel with 0.2% of C (AISI 1020).

After annealing it shows a lower

and upper yield stresses of about

55 ksi and a rupture strength of 6555 ksi and a rupture strength of 65

ksi (circles).

After a permanent deformation of

8%, the lower and upper yield

stresses disappear (green

triangles).

After 30-minute heating at 625 C

the yield stress of 77 ksi is reached

Prof. G. Ubertalli

the yield stress of 77 ksi is reached

(blue squares).

The work hardened material shows a very low rupture strain with respect to the annealed

material. After the last type of thermo-mechanical treatment, an increase of strength is

obtained, without loss of deformability.

Solid Solution

The increase of

the strength of

1000

Strenght gain in respect of iron [MPa]the strength of

the solid solution,

induced by the

presence of

different metallic

elements in solid

solution in the

lattice.

10

100

Strenght gain in respect of iron [MPa]

Prof. G. Ubertalli

lattice.

1

0,1 1 10

Strenght gain in respect of iron [MPa]

Solute percent in volume

Cr Mn Co Al, V Ni

Mo Si, W Ti Be

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Solid Solution II

(A) (B) (C)

Examples of local residual stresses (dash circles) in

case of solute atoms and edge dislocation:

Prof. G. Ubertalli

case of solute atoms and edge dislocation:

(A) Substitution atom of the same type of solvent atoms.

(B) Smaller substitution atom

(C) Larger substitution atom.

Solid Solution III- curve of a low carbon steel characterized by

lower and upper yield strengths, the Lders bands,

strain hardening, necking and sample rupture.

L

u

d

e

r'

Strain hardening

Yield stress- high- low

Prof. G. Ubertalli

B

a

n

ds

r'

s