Engineering Materials & Metal

8/11/2019 Engineering Materials & Metal

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ENGINEERING MATERIALS AND

METALLURGYAUTONOMOUS

For fourth SEMESTER(II YEAR)

PREPARED BYS.ARAVINDHA BALAJI

ASSISTANT PROFESSORDEPARTMENT OF MECHANICAL

ENGINEERING SONA COLLEGE OF TECHNOLOGYSALEM:636005



ENGINEERING MATERIALS ANDMETALLURGY

Application of EMAM(In Industry):Steel industry( e.g. steel plants, (SAIL) Essarsteels, jindal steel ltd.(JSW))

Pipe maufacturing industry, Plasticindustry. Some jewelry industry(Grades of the gold) Manufacturing industry.

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OBJECTIVE

Knowledge on the structure

Properties of the materials Treatment Testing and applications of metals and non-metallic

materials Suitable materials for various engineering application

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Review (Not for Exam)

Crystal structure

BCC, (Body cubic centre) structure

FCC, (Face cubic centre) structure and

HCP, (Hexagonal close packing)structure Unit cell

Crystallographic planes and directions

Miller indices

Crystal imperfections for point, line, planar and

volume defects.






UNIT:I CONSTITUTION OF ALLOYS ANDPHASE DIAGRAMS

Constitution of alloys-Solid solution,substitutional and interstitial-Phasediagrams, Isomorphous, eutectic,peritectic, and peritectroid reactions,Iron-Iron carbon equilibrium diagram.

Classification of steel and cast Iron,Microstructure, Properties andapplications.

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UNIT:II HEAT TREATMENTDefinition- Full annealing, stress relief,

recrystallisation and spheroidizing-normalising, hardening and tempering ofsteel. Isothermal transformationdiagrams-cooling curves superimposed onI.T.diagram, CCR-Hardenability, Jominyand quench test- Austempering,Martempering-case hardening-carburising, nitriding, cyaniding,carbonitriding, flame and inductionhardening .

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UNIT:IIIMECHANICAL PROPERTIES AND TESTING

Mechanism of plastic deformation, slip and

twinning-types of fracture-testing of materialsunder tension, compression and shear loads-Hardness tests (Brinell, Vickers and Rockwell),Impact test-Izod and charpy, Fatigue and creeptests, fracture toughness tests.

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UNIT:IVFERROUS AND NON FERROUS METALS

Effect of alloying elements on steel(Mn, Si,

Cr, Mo, V, Ti & W) – Stainless and tool steels – HSLA-maraging steels-Cast irons-Grey,White malleable, spheroidal-Graphite, Alloycast irons,

Copper and copper alloys-Brass, Bronze andCupronickel-Aluminum and Al-Cu alloy-Precipitation hardening-Bearing alloys.

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UNIT VNON-METALLIC MATERIALS

Polymers-Types of polymer, commodity and

Engineering polymers-properties andapplications of PE, PP, PS, PVC, PMMA, PET,PC, PA, ABS, PI, PAI, PPO, PPS, PEEK, PTFE

Polymer-Urea and Phenol formaldehydes-

Engineering ceramics-Introduction to fiberreinforced plastics.

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Metals and alloys Ceramics andglasses

Polymers

Engineering Materials

Application

Structures Machines Devices

Each category of engineering application requires material from any or all ofthese three group of materials




Organic polymers Plastics,Pvc,PTFE,polyethylene

Fibers:Terylene,nylon,cotton,natural, and

syntheticrubbers ,leathers

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Metals and alloysSteels, aluminum,

copper, silver,gold, Brasses,,

bronze s, maganininvar, super alloys boron rare earthmagnetic alloys

Ceramic andglasses

Mgo, cds, Al 2O3,

S iC, BaTio 3,Silica,

soda-time-glass,Concrete, cement

ferrites and garnetsceramic

superconductors

Glass fiber- reinforcedplastics

S i , G e ,

G a A s ,

B o r i d e -

r e i n f o r c e

d s t e e

l

M e t a l -

r ei nf o

r c e

d pl a s t i c s




Structure:The internal structure of a material,

simply called the structure.

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N ON -M ETALLIC M ATERIALS :

PE (polyethylene)PP (Polypropylene)PS(Polystyrene)

PMMA(Polymethyl methacrylate)PET(Polyethylene teraphthalate)PC(Polycarbonates)PA(Polyamides)

ABS(Acryknitrile-Butadiene-styrene) PI(Polyimide)

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N ON -M ETALLIC M ATERIALS :

PAI( Polyamideimide) PPO(Polyphenylene oxide) PPS(Polyphenylene sulphide)

PEEK(Polyether ether ketone) PTFE(Polytetra fluoro ethylene)

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UNIT:I CONSTITUTION OF ALLOYS ANDPHASE DIAGRAMS

Constitution of alloys-Solid solution, substitutionaland interstitial-Phase diagrams Isomorphous,eutectic, peritectic, and peritectroid reactions,

Iron-Iron carbon equilibrium diagram.

Classification of steel and cast Iron,Microstructure, Properties and applications.

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UNIT:ICONSTITUTION OF ALLOYS

AND PHASE DIAGRAMS CONSTITUTION - establishment, foundation,

creation, formation, structure, organization,

charter, bill.

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UNIT:ICONSTITUTION OF ALLOYS

AND PHASE DIAGRAMS SOME TECHNICAL TERMS AND

DEFINITIONS:

1.SYSTEM: It is a combination of phases of one ormore components.

2.PHASE: It is a Physically and chemically

homogenous part of a system under study, one

phase is different from the other in structure or

composition

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UNIT:ICONSTITUTION OF ALLOYS AND

PHASE DIAGRAMS 3.COMPONENTS:

The elements present in the

system are called component. A system may

consist of two or more components.

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CONSTITUTION OF ALLOYS AND PHASE DIAGRAMS

CONSTITUTION OF ALLOYS:4.ALLOY:

An alloy is defined as a combination of two or

more elements, of which one of the element should be

a metal in major proportion.

The others could be metals or non-metals, for eg:

Brass (CU-Zn), Steel (Fe-C)

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CONSTITUTION OF ALLOYS AND

PHASE DIAGRAMS

Alloy find very wide application in the industry than pure metals.

Uses of pure metals

1. High electrical conductivity

2. High ductility

3. Corrosion resistance are required.

These properties are generally at a maximum value in pure metals.

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PHASE DIAGRAMS

Mechanical properties

1. Tensile strength

2. Yield point

3. Hardness are

improved by alloying.

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UNIT:ICONSTITUTION OF ALLOYS AND PHASE

DIAGRAMS

CLASSIFICATION OF ALLOYS1 / 5

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CLASSIFICATION OF ALLOYS

Pure metals Solid

Solution

Intermedia

te phase




PHASE DIAGRAMS

Alloy can be either a single phase or a mixture

of phases.

A phases is anything which is homogeneous and

physically distinct.

In solid state alloys of three are three possible

phase.

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PHASE DIAGRAMS

If an alloy has a single phase, it could be either

a solid solution or an intermediate phase.

If the alloy is a mixture it could be composed ofany combination of the above three phases.

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UNIT I




PHASE DIAGRAMS

The major element which is large inamount is called base metal or parentmetal or solvent.

The other element that is lesser inamount is called the alloying element orsolute, it is the minor part (such as salt orsugar which is less in amount, beingmixed in water- solvent).

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UNIT I




PHASE DIAGRAMS

5. MIXTURE:It is a material more than one phase.

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UNIT:I




PHASE DIAGRAMS 1 / 5

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SOLID SOLUTION

SubstitutinalSolid solution

Interstitialsolid solution

Disordered(or) Random

Ordered(or) regular

UNIT I




PHASE DIAGRAMS

Solid solutions: A solid solution is the simplest type of alloys.

A Solution can be defined as a homogeneous mixture

in which the atoms or molecules of one substance are

dispersed at random into another substance.

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UNIT I




PHASE DIAGRAMS

A solid solution may be defined as a solidthat consist of two or more elementsatomically dispersed in a single-phase

structure. A solid solution is composed of two parts.

1 . Solute: A solute is the minor part ofthe solution or the material which isdissolved.

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UNIT I




PHASE DIAGRAMS

2. Solvent: Solvent constitutes the major portion of

the solution.

Both the solute and the solvent can be solid,

liquid or gas.

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UNIT I




PHASE DIAGRAMS

Solid solution:

Simply a solution in the solid state.

Solid solution may be defined as a

solution In the solid state which consists of two

kinds of atoms combined in one type of space

lattice.

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UNIT I




PHASE DIAGRAMS

space lattice:

Space lattice is defined as an array of

points in three dimensions in which every point

has surroundings identical to that every other

point in the array.

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S OLID SOLUTION

Case: In certain cases, the solidification of analloy results in the formation of one kind ofcrystal. In which both metals are present, but theycannot be detected by the microscope Although properties of the crystals areprofoundly( deeply,strongly ) changed.

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S OLID SOLUTION

In such a case we have a solid metal in which the

interatomic state which existed in the liquid solution

has been persevered after solidification , and it is

known as a solid solution.

In a solid solution the atom occur in a definite

geometrical pattern, which is usually a slightly

distorted form of one of the constituent metals.

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S OLID SOLUTION

Soildsolution are conductors, but not so good asthe pure metals on which they are based.

Some examples of solid solutions are: Cu-Zn alloys (Brasses) Ni-Cu alloys (Monel metal) Au-Ag alloys(Sterling silver) Fe-Cr-Ni alloys (Certain stainless steels)

Fe-C alloys (Steels)

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S UBSTITUTIONAL SOLID SOLUTION 1 / 5

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Solute AtomsSOLVENT OR

MATRIX ATOMS

solute-Atom of Metal-B Solvent-Atoms of zinc Metal-Azinc(Solute) Copper(Solvent)

Disordered substitutinal solid solution(random,)



S UBSTITUTIONAL SOLID SOLUTION

Ordered subsitutional solid solution 1 / 5 / 2 0 1

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SoluteAtoms

SOLVENT ORMATRIX ATOMS




In substitutional solid solution, there is a direct

substitution of one type of atom for another.

so that solute atoms(cu) enter the crystal to take

positions normally occupied by solvent atoms (e.g.,

Nickel atoms);

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The alloy is said to be in a disordered condition if

in the formation of a substitutional solid

solution, the solute atoms do not occupy any

specific position but are distributed at random in

the lattice structure of the solvent.

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An ordered subsititutional solid solution is shown

fig Cu-Zn, Al-Cu, α -Brass are some examples of

ordered structures.

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INTERSTITIAL SOLID SOLUTION

The four elements hydrogen, carbon, nitrogen,

and boron have such small diameters that they

can occupy the empty spaces (Interstices) in the

crystal lattices of many metals.

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INTERSTITIAL SOLID SOLUTION 1 / 5

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Solvent ormatrix atoms Solute atoms


CARBON(solute)

IRON( SOLVENT)




Interstitial solid solution usually have a limited

composition range and are generally considered

of secondary importance, but there are a few

instances worthy of special attention.

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The interstitial solution of carbon in iron

constitutes the basis of steel hardening.

Very small amount of hydrogen introduced into

steels during acid pickling(cleaning), plating, or

welding operations causes a Sharpe decrease in

ductility, known as hydrogen embrittlement.

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Interstitial nitrogen is useful not only in

nirtriding process but also as an important factor

in maintaining 18Cr-8Ni

Stainless steel in the austenitic condition.

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HUME - ROTHERY’S RULES OF SOLIDSOLUBILITY

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Hume - Rothery’s Rules of solid solubility



H UME - R OTHERY ’S R ULES OF SOLID SOLUBILITY

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Hume - Rothery’s Rules of solid solubility




HUME –ROTHERY’S RULES OF SOLID SOLUBILITY

The solubility limit of solute in solvents depends on

various factors. These were stated by Hume-rothery

and are as follows:

1. Critical structure factor (or) Crystal structure:

Metals that have the same crystal stucture (Lattice

structure) have a greater solubility.

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3. Chemical affinity factor (or) Electronegativity:

Formulation of solid solution is

favoured for metals that have less chemical affinity

is more, then a compound is formed instead of a solid

solution.

The metal which are separated in widely in theperiodic table are not suitable for making alloys

because of their high affinity.

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4. Relative valency factor(or)valence:

A metal that has a higher valency will

disslove only a small amount of a lower valency

metal, where as the metal with low valency

will have good solubility for the higher valency

metal.

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In some alloys both interstitial and

substitutional solid solution are formed to an

appreciable extent.

For Eg: A Cr-Ni steel contains interstitially

dissolved carbon and substitution ally dissolved

chromium, nickel, and minor elements.

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P OSSIBILITIES OF SOLID SOLUTIONS

• There are three possible solid solutions based on

the amount of their elements. They are:

1.Unsaturated solid solution: In the solvent is

dissolving small amount of solute as well as at a

given temperature and pressure, it is called

unsaturated solid solution.

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2. Saturated solid solution:

If the solvent is dissolving

limiting amount of solute, it is called saturated

solid solution.

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3. Supersaturated solid solution:

If the solvent is dissolving more of solute that it

should, under equilibrium, it is called

supersaturated solid solution.

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PHASE DIAGRAM

Types of phase diagram

1. Isomorphous

2. Eutectoid system

3. Eutectic system

4.Peritectic system

5. Peritectroid reactions

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PHASE DIAGRAM

Phase Diagrams

Phase diagrams are graphical

representation of what phases are present in an

alloy system at various

Temperatures, pressures, and compositions.

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PHASE DIAGRAM

(or)

A phase diagram is a map showing thestructure or phase present as thetemperature and overall composition ofthe material are varied.

Phase diagrams are also known as equilibrium

diagrams or constitutional diagrams .

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WHY SHOULD PHASE DIAGRAMS BE STUDIED ?

The phase diagrams can answer the following

important questions:

What condition is the material in?

Is the composition uniform throughout ?

If not, how much of each component is present?

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Is something present that may give undesired

properties?

What will happen if temperature is increased or

decreased; pressure is changed or composition is

varied?

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Phase diagrams are used by engineers and

scientists to understand and to predict many

aspects of the behavior of materials.

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TERMINOLOGY USED IN PHASE DIAGRAMS

1. Components

2. System

3. Alloy

4. Solid solution

5. Solute Solution

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6. Solvent

7. Phase

8. Equilibrium

9. Solubility limit

10.Degrees of freedom

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The various terms used in the study of phase

diagrams have been explained below:

1. COMPONENT: Component are pure metals

and or compounds of which an alloy is composed.

Eg: In a copper-zinc brass, the components are

CU and Zn.

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2. SYSTEM: The system has two meanings in this

context

i. System: May refer to a specific body of

material under consideration. For Eg: A

ladle of molten steel is referred as a system.

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(ii)system: May also refer to the series of possible

alloys consisting of the same components. For

example, the Iron-Carbon system.

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A system having one components is called a

Unary system, and the system having two, three

and four components are known as Binary,

ternary and quaternary systems, respectively.

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3. ALLOY:

An alloy is a mixture of two or more metals

or a metal (metals) and a non-metal (non-metals).

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4.SOLID SOLUTION:

It is a solid that consist of two or

more elements atomically dispersed in a single-

phase structure.

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5. SOLUTE SOLUTION:

It is the minor part of the

solution or the material which is dissolved.

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6. SOLVENT:

The material which contributes the

major portion of the solution.

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7. PHASE:

A phase may be defined as a homogenous

portion of a system that has uniform physical

and chemical characteristics.

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8. EQUILIBRIUM:

Equilibrium is said to exit when

enough time is allowed for all possible reactions

to be completed.

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The equilibrium state refers to the

characteristics of the system that remain

constant indefinitely. Equilibrium occurs when

the free energy of the system is at its minimum

value.

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The term phase equilibrium refers to

equilibrium as it applies to systems in which

more than one phase may exist.

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9. SOLUBILITY LIMIT:

It is the maximum concentration of

solute that may be added without forming a new

phase.

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NOTE: The addition of solution in excess

of the solubility limit results in the formation of

another solid solution or compound.

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10. DEGREES OF FREEDOM:

It is the number of

independent variables ( such as temperature,

pressure, and composition).

That can be changed independently without

changing the phase or phases of the system.

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WHAT IS MEANT BY THE TERM PHASE ?




A phase may be a portion of matter which is

homogenous

A phase may be defined as any physical distinct

homogenous and mechanically separable portion

of a substance.

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In Layman’s term, a phase requires a unique

structure, uniform composition, and well-defined

boundaries or interfaces

Examples: A pure substance such as water is a

single phase.

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The pure substance water can exist in solid,

liquid and vapour, each of these states being a

single phase, as shown in fig (a)

Now consider the effect of adding salt(Nacl) to

water. Salt will dissolve in water to give a

homogeneous solution.

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Thus the salt- water solution forms a single

phase as shown if fig(b)

If more salt is added into water, then we have

two different phases as shown if fig(c)

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A Single phase system is also termed as

“homogeneous system”

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System composed of two or more phases are

termed as mixtures or heterogeneous systems’.

Fig (d)

Most metallic alloys, ceramic, polymers, and

composite are heterogenous.

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ILLUSTRATION OF PHASES

WATER(2)

ILLUSTRATION OF PHASES:

(A) Three forms of water: 1) Ice 2)water 3)water vapour are each a phase.

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WATER

ICE (1)

WATER VAPOUR(3)




salt

(b) Salt and water have unlimited solubility(Homogeneous solution)- from a single phase

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C H

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C T

•




(C) Salt and water have limited solubility(Heterogenous solution)-from two distinct phases

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C H

S ONA

C T

Saturated brine

Excess salt





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S ONA

C T

OIL

WATER

OIL AND WATER HAVE VIRTUALLY NO SOLUBILITY FROM TWODISTINCT PHASES

PHASE DIAGRAM OF PURE



PHASE DIAGRAM OF PURESUBSTANCE

One- Component Phase diagram1

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1

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A pure substance such as water can exist in

solid, liquid, or vapour phases, depending on the

condition of temperature and pressure

1

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The phase relationships may be represented on

a pressure- temperature (PT) diagram, known as

a one-component (or unary) phase diagram, for

the H 2O System.

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The phase diagram is composed of regions of

pressure and temperature where only a single

phase is stable.

The line OA indicates the vapourisation line

and the line OB indicates the freezing line.

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Liquid and vapour phase exist along the

vapourisation line and liquid and solid phases

along the freezing line, shows in figure. These

lines are also known as Two phase equilibrium

lines.

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The point “O” is know as Triple point.

Triple point is the point at which three phases

(Solid, liquid, and vapour phases(gas)).

of a single material coexit. This triple point of

water exists at temperature 0.00980C

and at pressure 4.58 mm of Hg.

1

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S ONA

C T

PHASE DIAGRAMS



PHASE DIAGRAMS

The properties of an alloy depend on nature,

amount, size, distribution and orientation of the

phases.

A phase is the chemically and structurally

homogeneous portion of the microstructure.

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PHASE DIAGRAMS

It has the following characteristics

1. Same structure throughout.

2. Roughly the same composition and

properties throughout.

3. Definite interface between the phase

and surrounding.

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C T



J.W. GIBBS( J OSIAH W ILLARD G IBBS ) 1

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J.W. GIBBS( J OSIAH W ILLARD



(G IBBS )

JOSIAH WILLARD GIBBS PROPOSAL(OR)

J.W. GIBBS LAW

(OR) GIBB’S PHASE RULE

(or)

PHASE RULE

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C T



GIBBS PHASE RULE

J.W. Gibbs, American physicist derived an

equation which established relationship in a

system between the number of phases,

The number of degree of freedom and the

number of components.

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GIBB’S PHASE RULE

The phase rule indicates the phases that exists

at equilibrium.

The Gibb’s phase rule satisfies the following

relation:

P+F=C+n

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GIBB’S PHASE RULE

P- Number of phases that exist in a

system under certain conditions.

C-Number of components in the system.

n- It represents the number of variables,

examples: Temperature, pressure and

concentration.

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GIBB’S PHASE RULE

F- Degree of freedom. It is the number of

variables such as temperature or

pressure or concentration which can

be change independently without

changing the number of phases that

are present in the system.

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GIBB’S PHASE RULE

In most studies the pressure is constant

i.e., 1 atmospheric pressure and hence pressureis not considered a variable.

Usually the only variable under consideration istemperature and hence the Gibb’s phase rulebecomes;

P+F=C+1

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USES OF PHASE RULE

The phase rule predicts maximum number of

phases present in the alloy under equilibrium

conditions at any point of diagram.

If the number of phases are known, one can

determine the degree of freedom using phase

rule.

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USES OF PHASE RULE

Thus the phase rule is useful to know whether

the temperature or pressure or both variables

can be changed without changing the structure of

the alloy.

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ILLUSTRATION OF THE USE OF THE



PHASE RULE

Let us consider the application of gibbs phase rule

to the phase diagram of water system

Case 1 : Consider a triple point in the diagram. At the triple point, three phases coexist inequilibrium .

P=3. Since there is one component (water) in thesystem C= 1

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THE USE OF THE PHASE RULE

The number of degree of freedom can be

calculated using the Gibbs phase rule as,

F =1- 3+2F=0 (Zero degree of freedom)

This means that one of the variables

(Temperature or pressure) can be changed

at the triple point.

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ONA

C T




Note: Since the variables temperature or

pressure cannot be changed and still keep the

three phases of coexistence.

The triple point is called an invariant point.

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ONA

C T




Case 2: Next consider a point along liquid-solid freezing curve

P=2Then for water system

C=1 Applying the phase rule, we get:

F=1- 2+ 2F=1 (one degree of freedom)

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ONA

C T




This means that one variable

( Temperature or pressure) can be changed

independently and still maintain a system

with two coexisting phases.

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C

H S ONA

C T




Case:3Now consider a point on the phase

diagram of water inside a single phase in thiscase there will be only one phase present.

P=1 ,Then for water system, C=1Now the phase rule gives

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H S ONA

C T




F=1-1+2

F=2 ( two degree of freedom)

This means that two variables ( Temperature

and pressure) can be varied independently and

the system will still remain in a single phase.

1 / 5 / 2 0 1

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C

H S ONA

C T




Note: In many application (especially for most

binary alloy) the pressure is kept constant at 1

atmosphere.

In this case Gibbs phase rule is modified as

F=C-P+1

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H S ONA

C T




The above equation is known as condensed phase

rule.

This equation can be applied to most of

the binary phase diagram.

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C

H S ONA

C T



OBJECTIVE TYPE QUESTIONS

1. -----------May be visualized as forming from a

centre of freezing, or nucleus, which is composed

of a small group of atoms oriented into one of the

common crystal patterns.

Crystal

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C

H S ONA

C T



OBJECTIVE TYPE QUESTIONS

2.Perfect crystal of proper external shape can be

obtained only if crystallisation develops under

conditions

when degree of ----------------is very slight and the

metal has a very high purity.

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C

H S ONA

C T



V ARIOUS M ICRO -C ONSTITUENTS OF I RON -



C ARBON A LLOYS ARE :

1.Ferrite

2.Austenite

3.Cementite

4.Pearlite

5.Ledeburite

6.Martensite

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/ ME

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H S ONA

C T





7. Troosite

8. Sorbite, and

9.Bainite

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1. Ferrite (or α -Iron)

Ferrite is a primary solid solution based on α iron

having BCC structure.

It is Nothing but the interstitial solid solution of

carbon in iron.

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H S ONA

C T



F ERRITE 1

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Maximum solubility of carbon in iron is 0.025% carbon

at 723 °C, While its solubility at room temperature is

only 0.008%.

Ferrite is soft, ductile, and highly

Magnetic.

It can undergo extensive cold working

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2. Austenite (or γ -Iron)

Austenite is a primary solid solution based on γ

iron having FCC structure.

This is also an interstitial solid solution of

carbon in iron

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H S ONA

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A USTENITE 1

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A



A USTENITE

It is also a non-magnetic (paramagnetic)

Austentite has a greater electrical resistance

and coefficient of expansion than ferrite.

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C

H S ONA

C T

C



C EMENTITE

Cementite is the name given to the carbide of

iron(Fe 3c).

It is the hard, brittle, intermetallic compound of

iron with 6.69% of carbon.

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C

H S ONA

C T

C



CEMENTITE

The hardness and brittleness of cast iron is

believed to be due to the presence of the

cementite.

It is Magnetic below 250°c

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C

H S ONA

C T

C



CEMENTITE 1

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S ONA

C T

P



P EARLITE

Pearlite is the eutectoid mixture of ferrite

(87.5%) and cementite (12.5%).

It is formed when austenite decomposes

during cooling. It contains 0.8% of carbon

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P EARLITE



P EARLITE 1

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S ONA

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P



P EARLITE L AMELLAR -P EARLITE BEADED BAG 1

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S ONA

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P EARLITE



P EARLITE

The properties of pearlite is midway between

ferrite and cementite. It is relatively strong, hard

and ductile.

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S ONA

C T

LEDEBURITE



LEDEBURITE

Ledeburite is the eutectic mixture of austenite( γ -Iron) and

cementite (Fe 3C) Containing 4.3% carbon.

In pure iron-carbon alloy, it forms at 1140 °C.

Most of the engineering alloy materials belong to

this range of alloy.

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LEDEBURITE



LEDEBURITE 1

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S ONA

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LEDEBURITE



LEDEBURITE 1

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S ONA

C T

MARTENSITE



M ARTENSITE

Martensite is the super saturated solid solution

of carbon in α -Iron.

It is formed when steel is very rapidly cooled from the

austenitic state.

It exhibits a characteristic acicular or needle like

structure.

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MARTENSITE



M ARTENSITE

It is very hard more brittle and low ductility

properties.

There is an increase in specific volume during

formation of martensite from austenite.

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MARTENSITE



M ARTENSITE

As a result internal stresses are set up in the

materials leading to the formation of minute

cracks.

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M ARTENSITE (RED AND YELLOW MARTENSITE G REEN : AUSTENITE )



MARTENSITE . G REEN : AUSTENITE )1

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TROOSTITE



TROOSTITE

Troosite is the mixture of radial lamella of

ferrite and cementite. In fact, it differs from

pearlite only in the degree of fitness.

This constituents is also known as troostite

pearlite.

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TROOSTITE



TROOSTITE

It is the microstructure consisting ferrite and

finely divided cementite, produced on tempering

martensite below 450 °C

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TROOSTITE



TROOSTITE

It is formed by the decomposition of austenite

when cooled at a rate slower than that which

will yield a martensitic structure and faster than

that which will produce a sorbitic structure.

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TROOSTITE



TROOSTITE

It has hardness intermediate between

martensite and sorbite.

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S ONA

C T

TROOSTITE



TROOSTITE 1

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S ONA

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S ORBITE



S ORBITE

Sorbite is the microstructure consisting ferrite,

and finely divided cementite, produced on

tempering martensite above 450°C

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C T





S ORBITE



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S ORBITE



S O

Note:

All the pearlite, troosite and sorbite are ferrite-

cementite mixtures having lamellar structure.

However they are distinguished by their degree of

dispersion.

Pearlite has corase pearlite.

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S ORBITE



Troosite has fine pearlite

And sorbite has medium pearlite

1 / 5

/ 2 0 1

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B AINITE



Bainite is a decomposition product of austenite,

consisting of an aggregate of ferrite and carbide.

Bainite is obtained by transformation of pearlite

higher temperature ( has a feathery structure) is

called upper bainite.

1 / 5

/ 2 0 1

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B AINITE



Lower bainite provides high mechanical

properties and that is why it is extensively

used for components of machine and structures.

Bainite has hardness in between the hardness

of pearlite and martensite.

1 / 5

/ 2 0 1

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C H

S ONA

C T

B AINITE



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C T

IRON /C ARBON ALLOY P HASE D IAGRAM



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Documents

Engineering Materials & Metal