smithch01a - intro

8/4/2019 SmithCh01a - Intro

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CHAPTER

1

Introduction toMaterials Science

and

Engineering

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Adapted by Clinton Bemont from McGraw-Hills

Foundations of Materials Science and Engineering by

Smith and Hashemi


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Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display

The Mars Rovers - Spirit and Opportunity

Spirit and Opportunity are made up of materials such as

* Metals * Ceramics * Composites * Polymers * Semiconductors

www.nasa.gov


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What are Materials?

Materials may be defined as substance of

which things are composed or made.

We obtain materials from earths crust and

atmosphere.

Examples :- Silicon and Iron constitute 27.72

and 5.00 percentage of weight of

earths crust respectively.

Nitrogen and Oxygen constitute78.08 and 20.95 percentage of dry

air by volume respectively.

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Why the Study of Materials is Important?

Production and processing of materials constitute alarge part of our economies.

Engineers choose materials to suite application anddesign.

New materials might be needed for some newapplications.

Example :- Highly temperature resistant materials.

Space station and Mars Rovers are designed accordingto conditions in space.

* High pressure, low temperature, strong but light.

Modification of properties are needed for someapplications.

Example :- Heat treatment to modify properties.

Weve even named mankinds history by our abilityto manipulate materials (stone, copper, iron ages)

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Materials progress in engineering

Mechanical engineers: Lighter, higher

temperature, stronger

Electrical engineers: Energy efficiency,

energy storage, high temperature

Electronic engineers: Faster chips,

cooling, higher temperature operation

Civil engineers: Cheaper, higher strength,

lighter, more design compliant

Chemical engineers: Corrosion resistance,

catalysts


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Materials Science and Engineering

Materials science deals with fundamental

knowledge about the internal structure,properties and processing of materials.

Materials engineering deals with the application

of knowledge gained by materials science to

convert materials into products.

Resultant

Knowledge

of Structure andProperties

Applied

Knowledge

of Materials

Materials ScienceMaterials Science and

Engineering Materials Engineering

Fundamental

Knowledge

ofMaterials

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Well engineered &

competitive products


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Types of Materials - Metals

Metallic Materials (Metallic bonds, electron sharing)

Composed of one or more metallic elements.

Example:-Iron, Copper, Aluminum.

Metallic materials may contain nonmetallic

elements.

Example:- Carbon, nitrogen, silicon.

Inorganic and have crystalline structure.

Good thermal and electric conductors.

Metals and Alloys

Ferrous

Eg: Steel,Cast Iron

Nonferrous

Eg:Copper

Aluminum

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Metal alloys

An alloy is a combination of two or more metals (eg.

stainless steel = iron + chromium,7075 Aluminium = Al + Zn + Mg + Cu + Cr),

or a metal with a small amount of a non-metal

(eg. steel = Fe +


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Types of Materials - Polymers

Polymeric Materials (Plastics)(primarily covalent bonds, also Van Der Waals)

Organic (carbon backbone) giant molecules and mostlynoncrystalline.

These are produced through the process of polymerisation.

Some are mixtures of crystalline and noncrystallineregions.

Poor conductors of electricity and hence used asinsulators.

Low melting points.

Strength and ductility vary greatly.

Low densities and decomposition temperatures.

Thermoplastics (recyclable) and thermosets (not easilyrecyclable

Examples :-Poly Vinyl Chloride (PVC), Polyester, Epoxy,Rubber, Phenolics, Polyethylene, Polystyrene

Applications :-Appliances, DVDs, Fabrics, Packaging etc.

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C i h Th M G Hill C i I P i i i d f d i di l


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Types of Materials polymers

Hot = soft, Cold = hard

Permanently hardened

Structure between

Thermopolymer and

thermoset

Large recoverable strains

PropertiesType

Thermoplastics

Thermosets

Elastomers

Additives are oftenadded to plastics

(thermosets andthermoplastics).Fillers such as glass,clay, sawdust andlimestone are used.

C i ht Th M G Hill C i I P i i i d f d ti di l


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Types of Materials - Ceramics

Ceramic Materials (ionic bonds) Metallic and nonmetallic elements are chemically bonded

together (usually ionic but sometimes covalent) in molecules.

Inorganic but can be either crystalline, noncrystalline or

mixture of both.

High hardness, strength and wear resistance but brittle

Very good thermal (& electrical) insulators and very high

melting points. Hence used as inert refractories for furnace

linings for heat treating and melting metals inside.

Also used in space shuttle to insulate it during exit and

reentry into atmosphere. Other applications : Abrasives, construction materials,

crockery, piezoelectrics etc.

Example:- Porcelain, Glass, China, Silicon nitride, Silicon carbide,

tungsten carbide, cement1-7

Copyright The McGraw Hill Companies Inc Permission required for reproduction or display


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Types of Materials ceramics

Ceramics are mostly carbides, nitrides or oxides.

Ceramic glasses are usually a combination of silicon,

sodium and lime.

There is no definite transition between solid and liquid in

glasses, which gives glass its particular forming

capabilities.



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Types of Materials ceramics

Glass ceramics are a combination of glass and other

ceramic. Fine ceramic particles are held together by

crystallised glass, giving high thermal shock resistance.

Eg. porcelain and Pyrex-type cookware.

Bricks, tiles and other shapes are formed from moist

natural clay dried and fired at high temperatures.

Cements are ceramics such as lime, plaster of paris and

cement that harden at room temperature

Also abrasives such as silicon carbide and tungsten

carbide. These are hard but also relatively tough and

fracture resistant.

Advanced ceramics include several classes such as those

that are highly wear resistant, corrosion resistant,

temperature resistant and light. Used in car engines, jet and

rocket engines, armour plating. Also superconductors.



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Types of Materials - Composites

Composite Materials Mixture of two or more materials (phases or constituents)

- Resulting in a unique combination of properties.

Consists of a dispersed filler material (/reinforcing / fibers / particles)and a continuous binding (/matrix) material.

Materials only bond, will not dissolve in each other.

Matrix can be metal, ceramic or polymer

Primarily two broad types of composite:-

o Fibrous: Fibers in a matrix

o Particulate: Particles in a matrix

Properties are a function of the constituents, their relative amountsand the filler phase geometry. Thus toughness, strength and stiffness

can potentially all be optimised. Can be made temperature resistant.

Properties are usually anisotropic (different in different directions),not isotropic like eg. polymers.

Composites are not easily recyclable.

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Copyright The McGraw-Hill Companies Inc Permission required for reproduction or display


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Types of Materials composites

Categories:

o Particle reinforced composites: dispersed phase dimensionsapproximately the same in all directions.

o Fibre reinforced composites : dispersed phase fiber shapedlarge length-to-diameter ratio.

o Structural composites: combination of composites and

homogeneous materials which are either laminar or sandwichpanels.

Examples:

o Fiber Glass (Reinforcing material in a polyester or epoxy matrix)

o Wood (Organic fibers in resin)

o Concrete (Gravels or steel rods reinforced in cement and sand)

Applications:Aircraft structures and engines, bicycles, canoes, construction.



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Copyright The McGraw Hill Companies, Inc. Permission required for reproduction or display

Types of Materials composites

90 layup:



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Types of MaterialsElectronic (/Electric) Materials

Semi-conductors

Low volume but very important. Silicon is a common electronic (semi-conductor) material.

Its electrical characteristics are changed by adding impurities(doping).

100nm feature resolution

Examples:- Silicon chips, transistors

Applications :- Can you think of any?!

Others:

Capacitors & super-capacitors

Batteries

Circuit boards

Transformer cores

MEMS (Micro Electro-Mechanical Systems)

Motors, inductors & magnets

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Competition Among Materials

Materials compete with each

other to exist in new markets

Over a period of time usage

of different materials changes

depending on cost andperformance.

New, cheaper or better

materials replace the oldmaterials when there is a

breakthrough in technology

Example:-

0

200

400

600

800

1000

1200

1400

1600

lb/C

ar

1985 1992 1997

Model Year

Aluminum

Iron

Plastic

Steel

Predictions and use ofmaterials in US automobiles.

After J.G. Simon, Adv. Mat. & Proc., 133:63(1988) and new data1-10



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Copy g t e cG a Co pa es, c e ss o equ ed o ep oduct o o d sp ay

Future Trends

Metallic Materials

Production follows economic data closely.

Alloys are continually improved by betterchemistry and process control.

New alloys are always being researched, eg:

o Example: Nickel based high temperature superalloys.

o Aim: To improve both temperature and corrosionresistance while retaining high strength

New processing techniques are investigated.

o Example: Isothermal forging, Powder metallurgy.o Aim: To improve product life and fatigue

properties and reduce cost.

Metals for biomedical applications

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py g p , q p p y

Future Trends

Polymeric (Plastic Materials)

Fastest growing basic material (9%

per year average from 1930 to 1995).

After 1995rate ofgrowth decreased

due to partial application saturation.

Different polymeric materials can

be blended together to produce new

plastic alloys.

Search for new plastics continues to

be successful.

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py g p q p p y

Future Trends

Ceramic Materials

New families ofengineering ceramics have been

produced in the last decade

New materials and applications are constantly

found.

Now used in Auto and Biomedical applications.

Processing of ceramics is usually expensive and

costs must be reduced.

Often easily damaged as they are brittle.

Better processing techniques and high-impact

(high fracture toughness, less brittle) ceramics

must be found.

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Future Trends

Composite Materials

Fiber reinforced plastics are the most

widely used products.

On an average 3% annual growth.

Annual growth rate of 5% is predicted

for composites such as Fiberglass-Epoxy

and Graphite-Epoxy combinations.

Commercial aircraft use a greater and

greater proportion of composite

materials.

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Future Trends

Electronic Materials

Use of electronic materials such as silicon

has increased rapidly since 1970.

Electronic materials are expected to play

vital role in Factories ofthe Future.

Use of computers and robots will increase,

resulting in extensive growth in use of

electronic materials.

Aluminum for interconnections in

integrated circuits might be replaced by

copper resulting in better conductivity.

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Future Trends

Smart Materials : Change their properties bysensing external stimulus.

Shape memory alloys: Strained material reverts

back to its original shape above a critical

temperature.

Used in heart valves and to expand clogged arteries.

Used to open satellite collectors.

Used in unbreakable reading glasses/ sun-glasses

Piezoelectric materials: Produce electric field whenexposed to force and vice versa.

Used in actuators and vibration reducers.



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MEMS and Nanomaterials

MEMS: Microelectromechanical systems.

Miniature devices

Micro-pumps, sensors

Nanomaterials: Characteristic length < 100 nm

Examples: ceramics powder and grain size < 100 nm

Nanomaterials are inherently harder and strongerthan bulk materials due to their nano-sized features.

Some have biocompatible characteristics (as in

Zirconia)

Transistors and diodes are developed on nanowires.

Carbon nanotubes, etc.



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Case StudyMaterial Selection

Problem: Select suitable material for a bicycle

frame and fork.

Steel and

alloysWood

Carbon fiber

Reinforced

plastic

Aluminum

alloys

Ti and Mg

alloys

Low cost but

Heavy. Less

Corrosionresistance

Light and

strong. But

Cannot beshaped

Very light and

strong. No

corrosion.Very expensive

Light, moderately

Strong. Corrosion

Resistance.Expensive, fatigue

Slightly better

Than Al

alloys. But muchexpensive

Cost important? Select steel

Mechanical properties important? Select CFRP

smithch01a - intro

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