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Transcript of introduzione tmm_eng_col.pdf
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17/04/2012
1
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
Prof. G. Ubertalli
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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
Prof. G. Ubertalli
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)
Prof. G. Ubertalli
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.
Prof. G. Ubertalli
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