Basic Principles of SSW.

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INTRODUCTION ATOMIC BONDING FREE ENERGY
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Introduction to Atomic Bonding and Free Energy

• Lesson Objectives
• When you finish this lesson you will understand
• History, Background and Uses of Solid State
  Bonding
• Atomic and Molecular Bonding Principles
• Primary Secondary Bonds
• Free Energy Considerations and Adhesion

• Learning Activities
• View Slides
• Read Notes,
• Listen to lecture
• Examine Web Page
• Do on-line workbook
• View Demo
• 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
Definition

• 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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Linnert, Welding Metallurgy, AWS, 1994
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(No Transcript)
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Examine the Web Page
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Homework

• Submit Your Bio-sketch
• Do the Pre-Course Survey
• Email to get your student code

Dickinson.1_at_osu.edu
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Click on Edit Slides Notes Page View to see
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Examine Key Topic From Welding Encyclopedia
Look It Up
Dig Deeper About This
See Demo
Hear Explanation
Industrial Applications
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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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Advantages of Solid State Welding
Broad View for Motivation

• Eliminates liquid phases.
• Makes the joining of many dissimilar metal
  combinations possible.
• Can be applied at different temperatures and
  under different stresses
• 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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Disadvantages of Solid State Welding

• 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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Solid State Welding Materials
Materials

• 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 to stainless steel (tubular transition
  joint) by explosion welding.

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Solid State Welding Applications
Applications

• Bonding of stainless steel liners in aluminum fry
  pans.
• Aluminum cladding bonded to uranium fuel rods.
• Ultrasonic and thermo-compression bonding in the
  microelectronics industry.
• Friction welding in aero-space and automotive
  applications.

• Drill pipe.
• Intake / exhaust automatic valves.
• Bi-metallic pipe.

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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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Types of Solid State Welds
We Will Look At Each
Linnert, Welding Metallurgy, AWS, 1994
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Questions
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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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Atomic Bonds

• There are two major types of atomic bonds
• Primary bonds
• Secondary bonds
• Primary bonds are much stronger than secondary
  bonds.

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Primary Bonding

• Primary bonds include three types
• Ionic bonds
• Covalent bonds
• Metallic bonds

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Ionic Bonding

• Bonding takes place between metallic and
  nonmetallic elements.
• Metallic atoms give up valence electrons to
  nonmetallic atoms.
• Examples NaCl, MgO, CaCl2.

Na
Cl
Na
Na
Cl
Cl
Cl
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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Covalent Bonding

• Bonding between two atoms takes place by
  cooperative sharing of electrons.
• Examples Gas - N2, O2, CH4.
• Solid - carbon (diamond), silicon, germanium.

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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Metallic Bonding

• 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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Questions
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Secondary Bonding

• 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
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CoCl2 - 6 H2O
Ion - Dipole Interaction
Kotz, 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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Dipole - Induced Dipole Interaction
Kotz, Chemistry Chemical ReaCTIONS, Saunders
College Pub., 1999
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Induced Dipole - Induced Dipole Interaction
Kotz, Chemistry Chemical ReaCTIONS, Saunders
College Pub., 1999
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Kotz, Chemistry Chemical ReaCTIONS, Saunders
College Pub., 1999
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(No Transcript)
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Questions
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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).

From Materials Science and Engineering An
Introduction by W.D. Callister, John Wiley
Sons, 1985
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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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Free energy formation of a weld

• 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.

A
B
g0
g0
g0 and gAB are surface energies (surface
tension) of the free surfaces and grain
boundaries respectively.
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Summary for Similar Metals
Free energy formation of a weld
A
B
g0
g0
gAB
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Summary for Dissimilar Metals
Free energy formation of a weld

• A similar relationship can be developed for
  dissimilar metal welding showing a large negative
  (-) DG for all dissimilar metal combinations.

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Link to Bonding Demo
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End of Atomic Bonding
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Homework