1-1Intro Atomic Bonding Free Energy

8/8/2019 1-1Intro Atomic Bonding Free Energy

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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

[email protected]


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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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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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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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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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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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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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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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Induced Dipole - Induced Dipole Interaction


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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.


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


Summary for Similar Metals

A B


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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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1-1Intro Atomic Bonding Free Energy

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