Transcript Basic Principles of SSW.

Introduction
INTRODUCTION
ATOMIC BONDING
FREE ENERGY
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Introduction
Definition
Definition of Solid State Welding
A group of welding processes that
produces coalescence at
temperatures essentially below the
melting point of the base metal.
Pressure may or may not be used.
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Introduction
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Introduction
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Introduction
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Introduction
Introduction to Solid State Welding
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History of solid state welding dates back to very
ancient time.
Gold was hammered together by the ancients
earlier than 1000 B.C.
The iron framework of the Colossus of Rhodes was
forge welded in 280 B.C.
Versatility of fusion welding eclipsed solid state
welding in the first half of the 20th century.
Solid state welding experienced a rebirth in the
60’s and 70’s, especially in the field of microelectronics.
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Introduction
Broad View for Motivation
Advantages of Solid State Welding
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Eliminates liquid phases.
Makes the joining of many dissimilar metal
combinations possible.
Can be applied at different temperatures and under
different stresses
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At high temperature, where the atomic interaction range is
relatively large and solubility of contaminants is high, parts
can be joined together with less deformation.
At low temperature, where the atomic interaction range is
relatively small and solubility of contaminants is low, more
stress is needed to join two parts together and thus more
deformation is expected.
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Introduction
Disadvantages of Solid State Welding
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Surface preparation can be necessary.
Joint design is limited.
Elaborate and expensive equipment may be
required.
Non-destructive inspection is very limited.
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Introduction
Materials
Solid State Welding Materials
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Both similar and dissimilar metals can be welded.
Similar metal welds include:
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Titanium-to-titanium alloy (aircraft rivets) by friction
welding.
Ultrasonic welding of fine aluminum wire to aluminum
metallization in microelectronics.
Examples of dissimilar metal includes
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Aluminum to steel, titanium to aluminum, and titanium to
stainless steel (tubular transition joint) by explosion
welding.
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Introduction
Applications
Solid State Welding Applications
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Bonding of stainless steel
liners in aluminum fry pans.
Aluminum cladding bonded
to uranium fuel rods.
Ultrasonic and thermocompression bonding in the
microelectronics industry.
Friction welding in aerospace and automotive
applications.
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Drill pipe.
Intake / exhaust
automatic valves.
Bi-metallic pipe.
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Introduction
Applications
Solid State Welding
Explosion clad titanium
steel tube sheet blanks
Courtesy AWS handbook
180 inch diameter dome of 3/16 inch type
410 stainless steel on 3 inch thick A387 steel
formed from explosion weld.
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Introduction
Types of Solid State Welds
We Will Look At Each
Linnert, Welding Metallurgy,
AWS, 1994
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Introduction
Basic Principles
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In solid state welding,
joining of two surfaces
takes place by atomic
bonding between the
atoms on the surfaces.
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Introduction
Atomic Bonds
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There are two major types of atomic bonds
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Primary bonds
Secondary bonds
Primary bonds are much stronger than
secondary bonds.
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Introduction
Primary Bonding
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Primary bonds include three types:
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Ionic bonds
Covalent bonds
Metallic bonds
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Introduction
Ionic Bonding
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Bonding takes place
between metallic and
nonmetallic elements.
Metallic atoms give up
valence electrons to
nonmetallic atoms.
Examples : NaCl, MgO,
CaCl2.
Na+
Cl
Na+
Cl
Na+
Cl
Na+
Cl
Na+
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Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
Introduction
Covalent Bonding
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Bonding between two
atoms takes place by
cooperative sharing of
electrons.
Examples: Gas - N2, O2,
CH4.
Solid - carbon (diamond),
silicon, germanium.
H
H
C
H
H
Methane (CH4)
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Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
Introduction
Metallic Bonding
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Valence electrons are not
bound to any particular
atom and are free to drift
throughout the metal.
Remaining non-valence
electrons and atomic
nuclei form ion cores.
Free electrons act as a
glue to hold the ion cores
together.
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Introduction
Secondary Bonding
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Van der Waals bonds ( Ar, Kr, Ne).
Polar molecule-induced dipole bonds
(HCl, HF).
Hydrogen bonds ( H2O, NH3).
Bond energy only about 1/10 of
primary bonds.
Can cause adhesion of contaminants
to metal surfaces.
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Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
CoCl2 - 6 H2O
Ion - Dipole Interaction
Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
Dipole - Dipole Interaction
Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
Dipole - Induced Dipole Interaction
Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
Induced Dipole - Induced Dipole Interaction
Kotz, “Chemistry & Chemical ReaCTIONS”,
Saunders College Pub., 1999
Introduction
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Introduction
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Introduction
Adhesion of Perfect Metal Surfaces
10 A
Adhesion of metal
surfaces
occurs by
inter-atomic forces.
 For this to happen, the
two mating surfaces must
be brought together within
a very close distance.
 For most metals, this
distance is within a range
of approximately 10
angstroms (A).
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From: Materials Science and Engineering: An Introduction
by W.D. Callister, John Wiley & Sons, 1985
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Introduction
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Free energy formation of a weld
The potential energy of atoms at
the free surface is higher than that
of atoms within the bulk of the
solid.
The energy per unit area
possessed by atoms near the free
surface constitutes the free
surface energy.
The average surface atom has
about half the bonding energy of
an interior atom.
missing bond
A
B
Surface energy of A
is greater than B
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Introduction
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The welding of metal A to
metal B results in a
decrease in free energy
(DGweld).
This negative energy
difference (DGweld) creates
a driving force which
actually promotes
welding.
Free energy formation of a weld
A
B
g
g
0
A
0
B
g
AB
g0 and gAB are surface energies
(surface tension) of the free surfaces
and grain boundaries respectively.
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Introduction
Free energy formation of a weld
Summary for Similar Metals
DG
g
- 2g
AB
0
weld
g
 0.3g
AB
0
DG
 1.7g
0
weld
A
B
g
g
0
A
0
B
g
AB
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Introduction
Free energy formation of a weld
Summary for Dissimilar Metals
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A similar relationship can be
developed for dissimilar metal
welding showing a large
negative (-) DG for all dissimilar
metal combinations.
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Introduction
Link to Bonding
Demo
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