Materials Itroductions 2

7/28/2019 Materials Itroductions 2

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EGINEERING MATERIALS ANDMETALLURGY

A. NALLAPPANVSA SCHOOL OF ENGINEERING

SALEM


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MATERIALS SCIENCE AND ENGINEERING

MATERIALS SCIENCE

Its involving the relationships that exist between the structures

and properties of materials.

MATERIALS ENGINEERING

Materials engineering is on the basics of these structure-property

correlations, designing or engineering structure of a materials to

produce a predetermined set of properties.

The focus is on how to translate or transform materials into useful

devices or structures.


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WHY STUDY MATERIALS SCIENCE AND ENGINEERING ?

Right materials to right application


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CLASSIFICATION OF MATERIALS


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CLASSIFICATION OF MATERIALS

(contd.)

METALS

MATERIALS

POLYMERS CREAMICSALUMINA

SILICA

SILICON

CARBIDE

BORAN

CEMENTS

COMPOSITESPOLYWOOD

CONCREATR

CLASS

REINFORCE

PLASTIC

CORBON FIBER

THERMOPLASTIC

POLYMIDES

POLYCARBONATES

POLYSTYRENE

PVC

POLYETHYLENE

THERMOPLASTIC

POLYESTERS

PHEONAL

FORMALDEHYDE

UREA

FORMALDEHYDE

FERROUSIRON

STEEL

CASTIRON

NON FERROUSCOPPER

ALUMINIUM

LEAD

ZINC

COBALT

TIN


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Crystal physics


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CRYSTAL STRUCTURES

INTRODUCTION

The term crystal is a solid whose constituent atoms or

molecules are arranged in a systematic geometric

pattern.

The term structure means the arrangement of a

materials atoms; the structure at a microscopic scale is

known as microstructure.


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CLASSIFICATION OF SOLIDS

SOLDS


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CRYSTALLINE MATERIALS

Thematerialsinwhichtheatomsarearranged

insomeregularrepetitionpattern

Single crystal - Monocrystal

More than one crystalPolycrystallineExamples

steel

Gold

Silver

Copper


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NON CRYSTALLINE MATERIALS

In this type of materials, the atoms are

arrangedintheirregularfashion.

Examples

Glass

Rubber

polymers


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CRYSTALLOGRAPHY

Three-dimensionalarrangementsofatomsin

acrystaliscalledcrystallography

Its is refertotheseasthelattice and basisconcept and the unit cell concept


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LATTICE

LATTICE : A lattice is a arrangement of atoms

A lattice may be one-,two-, or three-dimensional.

LATTICE POINTS:

Its denote the position of atoms or molecules in the crystals.SPACE LATTICE :

Space lattice is a three-dimensional geometric

arrangement of the atoms or molecules or ions composing acrystal. Space lattice is also known as crystal lattice.

BASIS:

With a group of atoms attached to each lattice point calledbasis


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UNIT CELL

The smallest part of a crystal is called as unit cell. It is

formed by combination ofatoms and molecules. The

whole crystal structure can be formed by the

repetition of these unit cells.

S

S

S

S

S

S

S

S

S

S

S

S

S

S

2D 3D


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LATTICE GEOMETRY

To define the geometry of the unit cell in 3 dimensions we

choose a right-handed set of crystallographic axes,x, y,and z, which

point along the edges of the unit cell. The origin of our coordinate

system is at one of the lattice points.

The length of the unit cell along the x, y,and zdirection are defined

as a, b, and c. Alternatively, we can think of the sides of the unit cell

in terms of vectors a, b, and c. The angles between the

crystallographic axes are defined by


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LATTICE PARAMETERS

The length of the unit cell along the x, y, and z direction are

defined as a, b, and c. Alternatively, we can think of the sides of

the unit cell in terms of vectors a, b, and c. The angles between

the crystallographic axes are defined by:

= the angle between band c

= the angle between aand c= the angle between aand b

a, b, c,, , are collectively know as

the lattice parameters


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LATTICE PARAMETERS (contd)

PRIMITIVE CELL

Unit cell, which contains lattice points at its corners only.

NON-PRIMITIVE CELL

Unit cell, which contains more than one lattice points.


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CRYARAL TYPES

S.NO CRYSTAL SYSTEM NUMBER OF POSSIBLE TYPES1 CUBIC 3 (Simple, Body- centered, Face- centered)2 TETRAGONAL 2(Simple, Body- centered,)3 HEXAGONAL 1(Simple)4 ORTHORHOMIC 4(Simple, Body- centered, Face- centered,base- centered )5 RHOMBOHEDRAL 1(Simple)6 MONOCLINIC 2(Simple, Body-centered)7 TRICLINIC 1(Simple)


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CRYARAL TYPES (contd..)

Simple cubic structure

Body- centered cubic structure

Face centered cubic


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CRYARAL TYPES (contd..)


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CRYSTAL STRUCTURE

8- Corner atoms

SIMPLE CUBIC STRUCTURE (SC)


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BODY CENTER STRUCTURE(BCC)

8- Corner atoms and one center

atoms

Examples:

Tungsten (W),

Chromium (Cr),

vanadium (V),

Molybdenum (Mo),

-iron, - iron


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FACE CENTER CUBIC STRUCTURE (FCC)

CRYSTAL STRUCTURE (contd)

8-Corner atoms and one

atoms at the face

Examples:

Copper (Cu),

Gold (Au), Nickel (Ni), Platinum (Pt), Lead (Pb), Silver (Ag)


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HEXAGONAL CLOSE PACKED STRUCTURE (HCP)

8-One atoms at each corner, one atoms each at the center of the

hexagonal faces and three more atoms with the body of the cell

Examples:

Magnesium (Mg),

Zinc (Zn),

Titanium (Ti), Zirconium (Zr), Graphite, Diamond,

CRYSTAL STRUCTURE (contd)


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CRYSTAL DEFECTS OR IMPERFECTIONS

DEFECT (OR) IMPERFECTION

A perfect crystal, with every atom of the same type in the

correct position, does not exist. All crystals have some defects.

Any deviation from the perfect periodic repeated array of

atoms in the crystal.


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PURPOSE OF STUDYOF IMPERFECTION

IN CRYSTAL

Good understanding of crystal

How they affect the properties of metals

Help in finding the possibilities of redusing these defects


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0D

(Point defects)

CLASSIFICATION OF DEFECTS BASED ON DIMENSIONALITY

1D

(L ine defects)

2D

(Sur face / I nterface)

3D

(Volume defects/

bulk

Vacancy

Impurity

Frenkel

defect

Schottky

defect

Dislocation

Edge dislocation

Screw dislocation

Surface

Interphase

boundary

Grain

boundary

Twin

boundary

Twins

Precipitate

Faulted

region

Voids /

CracksStacking

faults

Disclination

Dispiration

Thermal

vibration

Interstitial


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POINT DEFECT

Point defects are where an atom is missing or is in an

irregular place in the lattice structure

(OR)

The defects which take place due to imperfection packing of

atoms during crystallization


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TYPES OF POINT DEFECT

Vacancy

Impurity

Frenkel

defect

Schottky

defect

Interstitial


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WHAT IS VACANCY ?

Vacancies are empty spaces where an

atom should be, but is missing.(OR)

Point defect means missing of the atoms in

the crystal, from the lattice site.

Tensile Stress

Fields ?

TYPES

a) Single vacancy

b) Di-vacancy


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SCHOTTKY DEFECT

When vacancies occur in an ionically bondedmaterial, a stoichiometric number of anions

and cations must be missing from regular

atomic positions if electrical neutrality is to be

preserved.


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I NTERSTITIAL DEFECT

An interstitial defect is formed when an

extra atom or ion is inserted into the crystal

structure at a normally unoccupied position


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SELF TNTERSTITIAL

Self-interstitial defects are interstitial defects which contain only

atoms which are the same as those already present in the lattice.

INTERSTITIAL DEFECT (contd..)


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Frenkel defect

A Frenkel defect is a vacancy-interstitial pair

formed when an ion jumps from a normal

lattice point to an inter

Frenkel defect can occur in metals and

covalently bonded materials stitial site,


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What is Impur ities (or) compositional defects ?

This defects arise when foreign atoms are present at

the lattice site or at the vacant interstitial sites.

Types:

1. Substitutional impurity

2. Interstitial impurity

Substitutional impurity

Foreign atom replaced a parent atom in the lattice.


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SUMMARY


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LINE DEFECT

Dislocation

I. Edge dislocation

II. Screw dislocation

Disclination

Dispiration


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WHAT IS DI SLOCATION ?

Dislocations are line imperfections in an otherwise perfect crystal.

(OR)

The defect, which take place due to dislocation or distortion of

atoms along a line

TYPES:

1. Edge dislocation

2. Screw dislocation

EDGE DISLOCATION


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EDGE DISLOCATION

This is plastic movement of atoms, which starts within the crystal

and their effect s can be seen on the edge of the crystal

(OR)

An edge dislocation can be illustrated by slicing partway through

a perfect crystal, spreading the crystal apart, and partly filling the

cut with an extra half plane of atoms.


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EDGE DISLOCATION


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EDGE DISLOCATION


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SCREW DI SLOCATION

The screw dislocation can be illustrated by cutting partway

through a perfect crystal and then skewing the crystal by one

atom spacing.


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SCREW DI SLOCATION


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SCREW DI SLOCATION


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SURFACE DEFECT (OR) PLANE DEFECTS

Surface defects are the boundaries, or planes, that separate a

material into regions

Surface

defect

Interphase

boundary

Grain

boundary

Twin

boundary

Stacking

faults


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The microstructure of many engineered ceramic and metallic

materials consists of many grains. A grain is a portion of the

material within which the arrangement of the atoms is nearly

identical; however, the orientation of the atom arrangement, or

crystal structure, is different for each adjoining grain

GRAIN BOUNDARY


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TILT AND TWIST BOUNDARIES

A small angle grain boundary is an array of dislocations that

produces a small misorientation (angle) between the adjoining

crystals.

TWIN BOUNDARIES


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TWIN BOUNDARIES

A twin boundary is a plane across which there is a special

mirror image misorientation of the crystal structure

TWIN BOUNDARIES

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Materials Itroductions 2