Constitution of alloys.ppt

8/15/2019 Constitution of alloys.ppt

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Engineering Materials andEngineering Materials andMetallurgyMetallurgy

Unit 1 - Alloys and Phase Diagrams

Unit 2 - Heat Treatment

Unit 3 - Ferrous and Non-ferrous Metals

Unit 4 - Non-metalli MaterialsUnit ! - Mehanial Pro"erties and Deformation

Mehanisms

06/08/16 10:09 Engineering Materials and Metallurgy 1


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Unit 1Unit 1

Alloys and Phase DiagramsAlloys and Phase DiagramsConstitution of alloys - Solid solutions, substitutional and

interstitial - phase diagrams, Isomorphous, eutectic, eutectoid,

peritectic, and peritectoid reactions, Iron - carbon equilibrium

diagram. Classification of steel and cast Iron microstructure,

properties and application.



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Constitution of AlloysConstitution of Alloys#u$%et &ode' M()4*3

Title' (ngineering Materials and Metallurgy


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General ObjectiveGeneral Objective

To study and understand the concepts of alloy

structure.

06/08/16 10:09 4Engineering Materials and Metallurgy


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Prere!uisite "no#ledgePrere!uisite "no#ledge

Engineering materials

Classification of engineering materials

Types of Crystal structure



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$%ecific Objectives$%ecific Objectives

Classify the solid solution.

Explain the general rules of Hume Rothery.

ifferentiate substitutional and interstitial solutions.



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AlloyAlloy

!n alloy is a substance that has metallic properties and iscomposed of t"o or more chemical elements, of "hich at least

one is a metal.

!lloys may be classified according to their struture, andcomplete alloy systems may be classified according to the

type of their equilibrium or phase diagram.

!lloys may be homogeneous (uniform) or mixtures. If thealloy is homogenous it "ill consist of a single phase, and if it

is a mixture it "ill be a combination of more than one phases.



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Possibilities of $olid $olutionsPossibilities of $olid $olutions

There are three possible solid solutions based on the amount oftheir elements. They are#

1,Unsaturated solid solution'

If the sol)ent is dissol)ing small amount of solute, it is

called unsaturated solid solution.

2, #aturated solid solution'

If the sol)ent is dissol)ing limiting amount of solute, it is

called saturated solid solution.

3, #u"ersaturated solid solution' If the sol)ent is dissol)ing more of solute than it should, it

is called supersaturated solid solution.



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&ume 'othery(s 'ules&ume 'othery(s 'ules

To form an extensi)e solid solution, the solute and sol)entelements should obey the general rules of Hume Rothery, that

control the range of solubility in alloy systems.

1, elati+e-#i.e fator# The si+e factor is fa)orable for solid-solution formation

"hen the difference in atomic radii is less than about 1

percent.

If the relati)e si+e factor is greater than $ percent, solid-solution formation is )ery limited.

ote# sil)er and lead /differene in atomi radii is 2* 0

solubility only .



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ContCont,,2, &rystal-struture fator#

Complete solid solubility of t"o elements is ne)er attainedunless the elements ha)e the same type of crystal lattice

structure.

3, elati+e-alene fator#

If the solute metal has a different )alence from that of thesol)ent metal, the electron ratio "ill be changed.

!he number of "alence electrons per atom is called election

ratio.

Crystal structures are more sensiti)e to a decrease in the

electron ratio than to an increases.

In other "ords, a metal of lo"er )alence tends to dissol)e more

of a metal of higher )alence than )ice )ersa.



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ContCont,,4, (letronegati+ity #

It is the ability of the atom to attract an electron.

The atoms must ha)e approximately the same

electronegati)ity. If electronegati)ity differ significantly,

then the compounds "ill form.

*y considering the abo)e four factors, some estimate of the solid

solubility of one metal in another can be determined.

It is important to note that an unfa"orable relati"e-si#e factor

alone is sufficient to limit solubility to a lo" )alue.

If the relati)e-si+e factor is fa)orable, then the other three factors

should be considered in deciding on the probable degree of solid

solubility.



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)y%es of $olid $olutions)y%es of $olid $olutions

$. (ubstitutional solid solutions

a/ Random

b/ 0rdered

&. Interstitial solid solutions

1, #u$stitutional #olid #olutions'

In substitutional solid solution, the atoms of the sol"ent

substitute for atoms of the solute in the lattice structure of

the sol)ent. This type of solid solution is quite common among )arious

metal systems



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ContCont,,

llustration'

! Ni-&u system, sho"n in

1igure, is an example for a

substitutional solid solution.

These t"o elements are

completely soluble in one

another at all proportions.

This system also satisfies all

the Hume Rothery2s rules.



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'andom $ubstitutional $olid $olution'andom $ubstitutional $olid $olution In random substitutional solid solution,

there is no order in the substitution ofthe t$o elements3 the solute and

sol)ent atoms are randomly

distributed.

In the formation of a substitutionalsolid solution, the solute atoms do not

occupy any specific position but


are distributed at random in lattice structure of the

sol)ent. This alloy is said to be in a random or disorderedcondition.

1igure illustrates a random substitutional solid solution of

copper-+inc system 4i.e., brass/. Here the crystal pattern is

not altered.


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Ordered $ubstitutional solid $olutionOrdered $ubstitutional solid $olution

If the solute and sol"ent atoms ta%e upsome preferred position, then the solution

is called ordered substitutional solid

solution or super lattice.

1igure sho"s an ordered substitutionalsolid solution.



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*nterstitial $olid $olution*nterstitial $olid $olution

These are formed "hen atoms of small atomic

radii fit into the spaces or interstices of the

lattices structure of the larger sol)ent atoms.

(ince the spaces of the lattice structure are

restricted in si+e, only atoms "ith atomic

radii less than 1 angstrom are li5ely to form

interstitial solid solution.

Interstitial solid solution can form only "hen

one atom is much larger than another.



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ContCont,,

These are hydrogen 46.78/, boron 46.9:/,

carbon 46.::/, nitrogen 46.:$/ and

oxygen 46.86/.

1igure illustrates an interstitial solid

solution that is formed by carbon in 1CC

; iron


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Mind Ma%Mind Ma%


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Objective )y%e +uestionsObjective )y%e +uestions$. ! single phase system are termed as >>>>>>>>>>>.

a/ Homogenous system

b/ Heterogeneous system

c/ Compound

&. 0ne angstrom is equal to >>>>>>>>>>>.

a/ $6-' m

b/ $6-$6 m

c/ $6-$' m

'. The (paces in the lattice structure are called as >>>>>>>>>>>.

a/ Interstices b/ Compound

c/ istortion



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$timulating +uestions$timulating +uestions,-o#er Order )echni!ue.,-o#er Order )echni!ue.

efine alloy.

?hat are the t"o types of solid solution@

ifferentiate random and ordered solid solution.

Aist out the )arious factors of hume rothery rules.



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$timulating +uestions$timulating +uestions,&igher Order )echni!ue.,&igher Order )echni!ue.

?hat is solid solution@ Explain the Hume Rothery rules

go)erning substitutional solid solution.

Ho" are solid solutions classified@ Bi)e t"o examples for

each.



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'eferences'eferences

Sidney H Avner, ntrodution to Physial

MetallurgyD Tata cBra"-Hill %ublishing Co.&66:


Constitution of alloys.ppt

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