1. intro to materials science

INTRODUCTION TO

MATERIALS SCIENCE

Introduction2

Materials make modern life possiblefrom the polymers in the chair youre sitting on, the metal ball-point pen youre using, and the concrete that made the building you live or work in to the materials that make up streets and highways and the car you drive.

All these items are products of materials science and technology

Materials science and engineering3

Materials Science investigating relationships that

exist between the structure and properties of

materials.

Materials Engineering on the basis of these

structure-property correlations, designing or

engineering the structure of a material to produce a

pre-determined set of properties

4 The combination of physics, chemistry, and the focus

on the relationship between the properties of a

material and its microstructure is the domain of

Materials Science.

The development of this science allowed designing

materials and provided a knowledge base for the

engineering applications (Materials Engineering).

5Evolution of materials

The world of materials7

8 2003 Brooks/Cole Publishing / Thomson Learning

Approach in Materials Science9

Materials, process and shape10

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2003 Brooks/Cole Publishing / Thomson Learning


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Structure15

At the atomic level: arrangement of atoms in

different ways (different properties for graphite

than diamond both forms of carbon.)

At the microscopic level: arrangement of small

grains of material that can be identified by

microscopy (different optical properties to

transparent vs. frosted glass.)

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graphite diamond

Materials, processes and choice

Engineers make things out of materials; to make

something out of a material you also need a

process;

Not just any processthe one you choose has to be

compatible with the material you plan to use.

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E.g. the materials have to support loads, to insulate

or conduct heat and electricity, to accept or reject

magnetic flux, to transmit or reflect light, to survive

in often-hostile surroundings, and to do all these

without damage to the environment or costing too

much.

Why do we study MSE24

Material properties

Mechanical properties

Thermal properties

Electrical, magnetic and optical properties

Chemical properties

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Properties are the way the material responds to the

environment; for instance, the mechanical, electrical and

magnetic properties are the responses to mechanical,

electrical and magnetic forces, respectively.

Other important properties are thermal (transmission of

heat, heat capacity), optical (absorption, transmission

and scattering of light), and the chemical stability in

contact with the environment (like corrosion resistance).

Mechanical properties29

The properties of a material are those that reveal

its elastic and inelastic (plastic) behavior when force

is applied.

Thereby, those properties will indicate its suitability

for mechanical (load-bearing) application, fatigue

limit, hardness, modulus of elasticity, tensile strength,

and yield strength.

Thermal properties

Thermal properties are

dependent on temperature;

therefore they are related to,

or caused by heat.

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This means that there is a limiting temperature

called the maximum service temperature, Tmax,

above which its use is impractical.

Stainless steel has a high Tmaxit can be used up to

800C; most polymers have a low Tmax and are

seldom used above 150C.

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Electrical, magnetic and optical properties

Electricity and magnetism are closely linked.

Electric currents induce magnetic fields; a moving

magnet induces, in any nearby conductor, an electric

current.

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The response of most materials to magnetic fields is too small to be of practical value.

Materials respond to light as well as to electricity and magnetismhardly surprising, since light itself is an electromagnetic wave.

Materials that are opaque reflect light; those that are transparent refract it, and some have the ability to absorb some wavelengths (colors) while allowing others to pass freely

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Chemical properties

A chemical property is any of a material's properties that becomes evident during a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity.

Chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected for its chemical properties to be investigated.

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Design-limiting properties

The performance of a component is limited by certain of the properties of the materials of which it is made.

This means that, to achieve a desired level of performance, the values of the design-limiting properties must meet certain targetsthose that fail to do so are not suitable.

Materials are chosen by identifying the design-limiting properties and applying limits to them, screening out those that do not meet the limits.

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Material family39

The process tree41

Process with shaping tree44

Process with joining and surface treatment tree45

Management for materials and processes46

Steel manufacturing process48

Typical mechanical properties51

The first two digits indicate carbon steel and the last two digits indicate the nominal carbon content in hundred of a percent

Example process: video52

Powder Processing

Powder processing relies on the semi-fluid character

of a powder to flow and fill a die at room

temperature, taking on the die shape.

Unlike machining where there is wasted material

and expense associated with mass removal, powder

approaches simply form the needed mass of

powder into the desired shape in a single step.

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Different from casting, which is only applied to

lower melting temperature metals, powder

techniques are applicable to all materials, including

diamonds, ceramics, and various compounds such as

tungsten carbide.

Indeed, many of the products formed using powders

are not available as castings.

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Powder injection molding55

A stainless steel pump

housing showing the

shape complexity

possible with powder

injection molding

and the size change

between molding (left

component) and sintering

(right component).

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Powder-binder extrusion

Powder-binder extrusion

is used to form a

product that is long and

thin with a constant cross

section, such as a rod,

tube, honeycomb, or

twist drill.

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Other powder method59

A slurry cast bronze statue formed using a wax-polymer binder, bronze powder, and rubber tooling. After the slurry was cast and cooled, the shape was placed in a furnace and slowly heated to burn out the binder and sinter the particles. This technology is ideal for smaller production quantities, such as encountered in the art field.

Ceramics Processing60

Ceramics injection molding61

Uniaxial pressing

Uniaxial (die) pressing involves the compaction of powder into a rigid die by applying pressure along a single axial direction through a rigid punch,plunger, or piston.

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Isostatic compaction63

Isostatic pressing, which is also known as isopressing, hydrostatic pressing, and cold isostatic pressing (CIP), provides a means of manufacturing complex shapes such as tubes and spark plug bodies, and larger volume parts that are not easily dry pressed.

Extrusion

Extrusion of (a) a rod and (b) a tube.

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Injection molding65

Slip Casting66

Tape casting67

Polymer processing

One of the most outstanding features of plastics is

the ease with which they can be processed.

In some cases semi-finished articles such as sheets or

rods are produced and subsequently fabricated

into shape using conventional methods such as

welding or machining.

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In the majority of cases, however, the finished article,

which may be quite complex in shape, is produced in a

single operation.

The processing stages of heating, shaping and cooling

may be continuous (e.g. production of pipe by

extrusion) or a repeated cycle of events (e.g.

production of a telephone housing by injection molding)

but in most cases the processes may be automated and

so are particularly suitable for mass production.

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There is a wide range of processing methods which may be used for plastics.

In most cases the choice of method is based on the shape of the component and whether it is thermoplastic or thermosetting.

It is important therefore that throughout the design process, the designer must have a basic understanding of the range of processing methods for plastics since an ill-conceived shape or design detail may limit the choice of molding methods.

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Screw extruder71

Extrusion stretch blow molding

Neck ring stretch blow molding

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Injection blow molding process73

Extrusion coating process74

References 75

B.S. Mitchell: An Introduction to Materials

Engineering and Science: for Chemical and

Materials Engineers, John Wiley & Sons, Inc.,

Hoboken, NJ, 2004

W.D. Callister, Jr.. Fundamentals of Materials

Science and Engineering, John Wiley & Sons, Inc.,

New York, 2001

1. intro to materials science

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