1. alloys and their properties

7/29/2019 1. Alloys and Their Properties

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Nofrijon

Sofyan, Ph.D.


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Basic Properties of Materials

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Introduction3

The properties of some materials are direcrelated to their crystal structures.

For example, pure and undeformed magneberyllium, having one crystal structure, are

more brittle (i.e., fracture at lower degreesdeformation) than are pure and undeformesuch as gold and silver that have yet anothstructure


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Furthermore, significant property differencebetween crystalline and noncrystalline mate

having the same composition.

For example, noncrystalline ceramics and pnormally are optically transparent; the sam

materials in crystalline (or semicrystalline) fto be opaque or, at best, translucent.


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Crystalline materials are solids whose atomare arranged in a pattern that is periodic idimensions.

In the contrary, amorphous materials do not

periodicity of a lattice, indeed their structurmore like a viscous liquid.


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The arrangement of atoms in solids, in genand ceramics, in particular, will exhibit lon

order, only short order, or a combination oSolids that exhibit long-range order are r

to as crystalline solids, while those in whicperiodicity is lacking are known as amorp

glassy, or non-crystalline solids.A lattice consisting of a repeating unit (thcell) arranged such that identical surrounexist everywhere one looks.


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(a) Long-range order;(b) short-range order


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A lattice consisting of a regularly repeated array(have translational symmetry)

Lattice points

containing one or

more atoms

The repeati

or unit cell

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Lattice or not?

This is a lattice

Why?

Each point hasidentical surroundings

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Lattice or not?

This is not a lattice

Why?

Surroundings of all

points are notidentical

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Why do we need to understand the crystal stAtomic level is a foundation for understand

physical properties of materials.

The structure of perfect crystals is basis forunderstanding defects in crystal and their mrelated physical properties.


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Crystalline and defect structure then can bethe foundation for understanding mass and

electrical transport in materials.

Crystallography is a powerful in another repermits the prediction of anisotropy in phys

properties from crystal symmetry.


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Crystal system

There are only a finite number of lattices that

the periodicity requirement for a crystalline ma

But the number of crystal structures far exceed

number of lattices that exist

How? Due to differences in what is located at lattice point (could be one or many but will befor all points)

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Motif

What sits at each lattice point is the motif

Motif + Lattice Crystal Structure

Consider the next example

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Motif

These two examples have the same 2D lattice, different crystal structure

One atom per lattice points Two atoms per lattice p

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Basic Questions:

Q: How does a crystal lattice differ from a cryststructure?

A: A crystal structure is built of atoms, whereas alattice is an infinite pattern of points, each ofmust have the same surroundings in the same

orientation. A lattice is a mathematical concepare only 5 different two-dimensional (planar)and 14 different three-dimensional (Bravais)

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All the unit cells shown describe the lattice

The lattice is not affected by the choice of unit cell

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Unit cell and lattice

The choice of unit cell is arbitrary so long acan be repeated

What we usually do is to use the simplest, m

symmetrical unit cell that will describe the la

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Two-dimensional lattices

There are only five two-dimensional lattices

Square Rectangular Oblique Diamond H

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Three-dimensional lattices

There are only 14 possible three-dimensional called Bravais lattices

Could we produces others? No, other lattices cdescribed by one of the 14 unit cells in the Bralattice set

Could we use more than one unit cell from amo14? Often, yes we could, but as with 2-D we usimplest most symmetrical as a convenience

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Nomenclature

P = simple, primitive

I = body centered

F = face centered

C = base centered

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Basic crystallography22

Crystal system Lattice symbol Lattice parameters

1. Triclinic aP a b c, 90o,

2. Monoclinic primitive mP a b c, = 90o,

Monoclinic centered mC

3. Orthorhombic primitive oP a b c, = =

Orthorhombic C-face-centered oC

Orthorhombic body-centered oI

Orthorhombic face-centered oF


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Crystal system Lattice symbol Lattice parameters

4. Tetragonal primitive tP a = b c, = = = 9

Tetragonal body-

centered tI5. Trigonal

(Rhombohedral) hR a = b = c, = = (p

a' = b c, = = 9

(hexagonal cell)

6. Hexagonal primitive hP a = b c, = = 90o,

7. Cubic primitive cP a = b = c, = = = 9

Cubic body-centered cI

Cubic face-centered cF


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Triclinic

a

b

c

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Primitive monoclinic

a

b

c

b

c

Base-centered mon

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Rhombohedral

a

c

120o

a

b c

Primitive hexagona

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ab

c

ab

c

a

c

Primitive orthorhombic Body-centered orthorh

Base-centered orthorhombic Face-centered orthorh

a

c27


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Primitive tetragonal Body-centered tetra

a

b

c

a

b

c

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a

b

c

Primitive cubic

a

b

c

Body-centered cubic

a

c

Face-centered

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Do we need only 14 Bravais?

At first sight this lattice sbe base centered tetra

i.e. not a Bravais lattice

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However, the lattice is asimple (or primitive) tetr

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M ?


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More than one Bravais?

FCC crystal lattice

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M h B ?


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More than one Bravais?

Body centered tetragon

lattice

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The FCC crystal shown could equally be deby a body centered tetragonal (BCT) lattice

However, we usually find the use of FCC asdescription far more convenient than BCT

In addition, X-ray diffraction peak of FCC

different from that of BCT

L i


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Lattice parameters

First identify the unit cell of the Bravais latt

Then define from one corner the crystallograxes defining the unit cell

The lengths of these axes define the lattice

parameters (or lattice constants of the cell) So long asx, y,z are orthogonal, the choic

which axis is which is arbitrary

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In a cubic crystal, a

In a tetragonal, a =

In an orthorhombic c

In non orthogonal c

we would also needspecify the angles bsome or all axes

z

x

yab

c

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C di t t


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Coordinate system

This means that we need a coordinate systedescribing planes

Cartesian or polar coordinate will not do a

describe location of points not planes

Miller indices are capable of addressingcoordinates for planes

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If plane does not cut

intercept =

Axis x y

Intercept 1 2/3

x

y

z

x

b

c

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Intercept 1 2/3

Invert 1 3/2 0

Clear fraction 2 3 0 (multiply throu

The Miller indices of a plane are written as

Here we have (2 3 0)

(h k l) = plane; and {h k l} = plane type


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In cubic systems (100), (010), (001), (100),

(001) all have similar forms and belong to

plane type {100} In tetragonal systems (100), (010), (100), (0

belong to {100} while (001), (001) belong

In tetragonal systems {100} {001}

Lattice planes and Miller indices


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Miller indices of lattice planes uses h,

k, and l: (a, b) (100); (c, d) (010);

(e, f) (001), (g, h) (110); (i) (111)

Lattice planes and Miller indices41

Hexagonal planes and Miller ind


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Hexagonal lattices andMiller-Bravais indices usesh, k, i, and l in which h + k

+ i = 0; or i = - (h + k)

Hexagonal planes and Miller ind42

Directions indices


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Directions indices

Direction [u v w] traalong a, v along balong c

This direction trave

along a, 1 along balong c

z

x

yab

c

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Axis x

Intercept 0Clear fraction 0

(multiply through by 2)

With directions [u v w] a specific direction,


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More directions

Direction in alattice is defined

by three indices: u,

v, and w.

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Identify them!


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a

Identify them!46

Directions hexagonal


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Directions, hexagonal47

Direction in a hexagonal

lattice uses four-indexsystem, [uvtw] calledWeber indices.

[uvw] [uvtw]

u = (2u v)/3v = (2v u)/3

t = - (u + v)w= w


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Alloys and their properties

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Introduction


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Introduction49

In the periodic table, 87 elements are class

metals, 61 of which are commercially avail

The most commonly used metals and alloys

based on Al, Cu, Fe, Ni, Pb, Sn and Zn.


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Definition


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Definition51

An alloy is a mixture or metallic solid solutio

composed of two or more elements.

An alloy will contain one or more of the thr

solid solution of the elements (a single phas

mixture of metallic phases (two or more solan intermetallic compound with no distinct b

between the phases.


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An alloy is a mixture of either pure or fairlychemical elements, which forms an impure s

(admixture) that retains the characteristics ometal.

An alloy is distinctive from an impure metalwrought iron, in that, with an alloy, the addimpurities are usually desirable and will typhave some useful benefit.

Terminology


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Terminology53

The primary metal is called the base, the m

the solvent whereas the secondary constitueoften called solutes.

If there is a mixture of only two types of at

counting impurities, such as a copper-nickel then it is called a binary alloy.

If h h f f h


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If there are three types of atoms forming thmixture, such as iron, nickel and chromium, tcalled a ternary alloy.

An alloy with four constituents is a quaternawhile a five-part alloy is termed a quinary

The percentage of each constituent can be

with any mixture the entire range of possibvariations is called a system: e.g. two consticalled binary system and so on.

All i l i d b bi i i i h


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Alloying a metal is done by combining it with omore other metals or non-metals that often enhproperties, for example, steel is stronger than

primary element. The physical properties, such as density, reactiv

Young's modulus, and electrical and thermalconductivity, of an alloy may not differ greatly

those of its elements, but engineering propertitensile strength and shear strength may be subdifferent from those of the constituent materia


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Pure metal

Interstitial alloy

Substitutional allo

Substitutional/Interstitial

Metals properties


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Metals properties57

noble metals - generally unreactive, e.g. sil

platinum, gold and palladium;

alkali metals - very reactive with low meltin

and soft, e.g. potassium and sodium;

lk li h l l i hi h


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alkaline earth metalsless reactive, higherpoints and harder than alkali metals, e.g. c

magnesium and barium; transition metals - hard, shiny, strong, and e

shape, e.g. iron, chromium, nickel, and copp

other metals diverse properties, e.g. alugallium, indium, tin, thallium, lead and bism

Hume Rothery: Substitutional allo


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Rule 1:

Atomic size factor or the 15% rule: extensivesubstitutional solid solubility may occur if the redifference between the atomic radii (r) of the elements is less than 15%, i.e.

for solid solubility,

15% Conversely, if the difference > 15%, solubility

generally is limited.

Rule 2


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Rule 2:

Crystal structures of the two elements must be for appreciable solid solubility.

Rule 3:

The solute and solvent atoms should typically hsame valency in order to achieve maximum so

For different valencies, a metal will dissolve a higher valency to a greater extent than one ovalency.

R l 4


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Rule 4:

Electronegativities need to be similar for m

solubility, i.e. a solute and solvent should bethe electrochemical series.

When the difference in electronegativities iintermetallic compounds tend to form rathesubstitutional solid solutions.

Interstitial alloys


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Interstitial solid solutions are more likely to be

if:

a solute is smaller than the interstitial sites i

solvent lattice of a solvent;

a solute has approximately the sameelectronegativity as the solvent.

In practice there are very few elements that c


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In practice, there are very few elements that cions which are sufficiently small to fit in intersti

and so appreciable solubility is rare for interstsolutions.

Possible metal ions that may form interstitial sosolutions are: Li, Na, B; plus non-ions H, C, N

Many interstitial solid solutions have a strong tto spontaneous ordering and examples of ordpartially interstitial solid solutions include Al-Li

Intermetallics


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Intermetallic compounds are metallic phases bu

the alloys described above, each generally halimited composition range, i.e. intermetallics ten

have a narrow and fixed stoichiometry.

Ordering within the crystal lattice is thus comm

One consequence is that typically they are quiand strong.

Major metallic alloy systems


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steelslow cost, high strength (over 90% b

of all metal usage is steel);aluminium alloyshigh specific strength, co

resistance, specific conductivity;

titanium alloys higher specific strength an


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titanium alloyshigher specific strength antemperature application;

copperhigh electrical & thermal conductieasy to form/cast, corrosion resistance;

nickelhigh temperature strength and creeresistance (superalloys).

Metals Industries Applications


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67 Steels Very wide Automotive, ships, b

white goods

Aluminium

alloys

Aerospace, packaging, sports

equipment, energy, construction

Aircraft, food conta

cables, building cla

Titanium alloys Biomedical, aerospace Body implants & m

military airframe a

spacecraft

Copper alloys Construction, electronics, coins,

transport

Plumbing, wiring, ci

electronic compone

Nickel

superalloys

Aerospace Aircraft engines an

References


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B.D. Cullity: Elements of X-ray Diffraction, 2nd e

Addison-Wesley Publishing Company Inc., ReaMassachusetts, 1978

R.J.D. Tilley: Crystals and Crystal Structures, Joh& Sons Ltd., Chichester, West Sussex, England,

W.D. Callister, Jr.. Fundamentals of Materials Sand Engineering, John Wiley & Sons, Inc., New2001

1. alloys and their properties

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