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8/8/2019 1-1Intro Atomic Bonding Free Energy
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Introduction
1998/SSW1/41/1
INTRODUCTION
ATOMIC BONDINGFREE ENERGY
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Introduction to Atomic Bonding and Free Energy
Lesson ObjectivesWhen you finish this lesson you will
understand:
History, Background and Uses of
Solid State Bonding
Atomic and Molecular BondingPrinciples
Primary & Secondary Bonds
Free Energy Considerations and
Adhesion
Learning Activities1. View Slides;
2. Read Notes,
3. Listen to lecture
4. Examine Web Page
5. Do on-line workbook
6. View Demo
7. Do Homework
Keywords: Solid State Bonding, Atomic Bonding, Primary
Bonds, Secondary Bonds, Ionic Bonding, Covalent Bonding,
Metallic Bonding, Free Energy
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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.
Definition
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Linnert, Welding Metallurgy,
AWS, 1994
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Submit Your Bio-sketch Do the Pre-Course Survey
Email to get your student code
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These PowerPoint Slides have Supplemental Information
Click on Edit Slides & Notes Page View to see Slide Notes
Or Click on Icons When They Appear on Page
Look It Up
See Demo
Examine Key Topic From
Welding Encyclopedia
Dig Deeper About This
Hear Explanation Industrial Applications
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Introduction
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Introduction to Solid State Welding
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
60s and 70s, especially in the field of micro-
electronics.
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Eliminates liquid phases.
Makes the joining of many dissimilar metalcombinations possible.
Can be applied at different temperatures and underdifferent stresses At high temperature, where the atomic interaction range is
relatively large and solubility of contaminants is high, partscan be joined together with less deformation.
At low temperature, where the atomic interaction range isrelatively small and solubility of contaminants is low, morestress is needed to join two parts together and thus moredeformation is expected.
Broad View for Motivation
Advantages of Solid State Welding
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Introduction
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Surface preparation can be necessary.
Joint design is limited.
Elaborate and expensive equipment may berequired.
Non-destructive inspection is very limited.
Disadvantages of Solid State Welding
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Both similar and dissimilar metals can be welded.
Similar metal welds include:
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
Aluminum to steel, titanium to aluminum, and titanium tostainless steel (tubular transition joint) by explosion
welding.
Materials
Solid State Welding Materials
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Introduction
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Solid State WeldingApplications
Bonding of stainless steelliners in aluminum fry pans.
Aluminum cladding bondedto uranium fuel rods.
Ultrasonic and thermo-compression bonding in themicroelectronics industry.
Friction welding in aero-space and automotiveapplications.
Applications
Drill pipe.
Intake / exhaust
automatic valves. Bi-metallic pipe.
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Introduction
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Solid State Welding
Applications
Explosion clad titanium
steel tube sheet blanks
180 inch diameter dome of 3/16 inch type
410 stainless steel on 3 inch thick A387 steel
formed from explosion weld.Courtesy AWS handbook
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Introduction
1998/SSW1/41/15Linnert, Welding Metallurgy,
AWS, 1994
Types of Solid State Welds
We Will Look At Each
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Basic Principles
In solid state welding,
joining of two surfaces
takes place by atomic
bonding between the
atoms on the surfaces.
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There are two major types of atomic bonds
Primary bonds
Secondary bonds Primary bonds are much stronger than
secondary bonds.
AtomicB
onds
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PrimaryB
onding
Primary bonds include three types:
Ionic bonds
Covalent bonds Metallic bonds
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IonicB
onding
Bonding takes place
between metallic and
nonmetallic elements. Metallic atoms give up
valence electrons to
nonmetallic atoms.
Examples : NaCl, MgO,
CaCl2.
Cl
Cl
Cl
Cl
Na+
Na+
Na+
Na+
Na+
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Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999
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Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999
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Introduction
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CovalentBonding
Bonding between two
atoms takes place by
cooperative sharing of
electrons.
Examples: Gas - N2, O2,
CH4.
Solid - carbon (diamond),silicon, germanium.
C HH
H
H
Methane (CH4)
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Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999
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Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999
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Introduction
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MetallicB
onding
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 aglue to hold the ion cores
together.
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SecondaryBonding
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 contaminantsto metal surfaces.
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Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999
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CoCl2
- 6 H2
O
Ion - Dipole InteractionKotz, Chemistry & Chemical ReaCTIONS,
Saunders College Pub., 1999
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Dipole - Dipole Interaction Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999
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Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999Dipole - Induced Dipole Interaction
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Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999
Induced Dipole - Induced Dipole Interaction
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Kotz, Chemistry & Chemical ReaCTIONS,Saunders College Pub., 1999
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Introduction
1998/SSW1/41/37From: Materials Science and Engineering: An Introductionby W.D. Callister, John Wiley & Sons, 1985
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, thisdistance is within a range
of approximately 10
angstroms (A).
Adhesion of Perfect Metal Surfaces
10 A
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The potential energy of atoms atthe 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 ofan interior atom.
B
A
Surface energy of Ais greater than B
Free energy formation of a weld
missing bond
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The welding of metal A to
metal B results in a
decrease in free energy
((Gweld.
This negative energy
difference ((Gweld)creates
a driving force which
actually promotes
welding.
A B
K K
K0
and KAB are surface energies
(surface tension) of the free surfaces
and grain boundaries respectively.
Free energy formation of a weld
A B
KAB
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(
(
Gweld AB
- 20
AB 0.3 0
Gweld
u
e
u
K K
K K
K170
.
A B
K
K
KAB
Free energy formation of a weld
Summary for Similar Metals
A B
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Free energy formation of a weld
Summary for Dissimilar Metals
A similar relationship can be
developed for dissimilar metal
welding showing a large
negative (-) (G for all dissimilar
metal combinations.
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Link to
BondingDemo
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