Materials Principles and Practice. Electronic Materials Manufacturing with Materials Structural Materials

396 Pages·1990·88.099 MB·English

by  Charles Newey and Graham Weaver (Eds.)

OTHER TITLES IN THE MATERIALS IN ACTION SERIES
ELECTRONIC MATERIALS
MANUFACTURING WITH MATERIALS
STRUCTURAL MATERIALS
,J
(p^\ \
MATERIALS
PRINCIPLES AND
PRACTICE
EDITED BY CHARLES NEWEY AND
GRAHAM WEAVER
9
TheOpen
University
OPENUN^RS^MSKE^SSS
Butterworths
LONDON BOSTON SINGAPORE
SYDNEY TORONTO WELLINGTON
First published 1990
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British Library Cataloguing in Publication Data
Materials principles and practice.
1. Materials
I. Newey, Charles II. Weaver, Graham III. Series
620.1Ί
ISBN 0-408-02730-4
Library of Congress Cataloging-in-Publication Data
Materials principles and practice/edited by Charles Newey and Graham Weaver.
p. cm.-(Materials in action series)
This text forms part of an Open University Materials Department course.
Bibliography: p.
Includes index.
ISBN 0-408-02730-4
1. Materials. I. Newey, Charles (Charles W. A.) II. Weaver, Graham
(Graham H.) III. Open University. Materials Dept.
IV. Series.
| TA403.M3455 1990
Butterworth Scientific Ltd
Part of Reed International P.L.C.
Designed by the Graphic Design Group of the Open University
Typeset and printed by Alden Press (London & Northampton) Ltd, London, England
This text forms part of an Open University course. Further information on Open
University courses may be obtained from the Admissions Office, The Open University,
PO Box 48, Walton Hall, Milton Keynes, MK7 6AB.
ISBN 0408 02730 4
Series Preface
The four volumes in this series are part of a set of courses presented by
the Materials Department of the Open University. The books are
nevertheless self-contained. They assume that you are just starting to
study materials, and that you are already competent in pre-university
mathematics and physical science.
Unlike many introductory texts on the subject, this series covers
materials science in the technological context of making and using
materials. This approach is founded on a belief that the behaviour of
materials should be studied in a comparative way, and a conviction that
intelligent use of materials requires a sound appreciation of the strong
links between product design, manufacturing processes and materials
properties.
The interconnected nature of the subject is embodied in these books by
the use of two sorts of text. The main theme (or story line) of each
chapter is in larger, black type. Linked to this are other aspects, such as
theoretical derivations, practical techniques, applications and so on,
which are printed in red. The links are flagged in the main text by a
reference such as τ Assessing hardness A, and the linked text, under this
heading, appears nearby. Both sorts of text are important, but this
format should enable you to decide your own study route through them.
The books encourage you to 'learn by doing' by providing exercises and
self-assessment questions (SAQs). Answers are given at the end of each
chapter, together with a set of objectives. The objectives are statements
of what you should be able to do after studying the chapter. They are
matched to the self-assessment questions.
This series, and the Open University courses it is part of, are the result
of many people's labours. Their names are listed after the prefaces. I
should particularly like to thank Professor Michael Ashby of Cambridge
University for reading and commenting on drafts of all the books, and
the group of student 'guinea pigs' who worked through early drafts.
Finally, thanks to my colleagues on the course team and our
consultants. Without them this project would not have been possible.
Further information on Open University courses may be had from the
address on the back of the title page.
Charles Newey
Open University
January 1990
Preface
To succeed in the market, products must — at least — use the right
materials and be made by efficient processes. Getting both the materials
and the processes right, from both the service and the manufacturing
points of view, is what we mean by the series title MATERIALS IN ACTION.
This book introduces that series.
We start in the context of production. We see that different materials
provide different 'portfolios' of properties. These determine what the
materials are suitable for, and how they may be processed. But
materials' properties can be modified, and understanding how requires
an appreciation of some basic science of materials. This is the nub of
the middle chapters, where the state of matter is modelled as a balance
between the tendencies of atoms to stick together (by chemical bonding)
or rattle apart (by thermal agitation). The last three chapters are about
property modification by control of microstructure. The agencies for
change here are thermal, mechanical and chemical.
All the chapters of the book have benefitted greatly from the comments,
criticisms and suggestions of our colleagues on the course team; we are
particularly grateful to Andrew Greäsley in this respect. Nick
Braithwaite was a co-author of Chapter 3, and we should like to thank
Nigel Mills and Peter Lewis for their important contributions to
Chapters 5 and 7 respectively.
We are especially indebted to our editor, Allan Jones, for his
forbearance and unstinting quest for clarity, to Andy Harding, our
course manager, for his indispensable help in making it all happen, and
to Phil Thompson, who took a large share of the burden of 'de-bugging'
each chapter. We should also like to thank our secretaries Lesley Phelps,
Lisa Emmington and Tracy Bartlett for working on so many (messy!)
drafts, and Naomi Williams and Richard Black for many of the
micrographs we have used.
Charles Newey and Graham Weaver
6
Open University Materials
in Action course team
MATERIALS ACADEMICS PRODUCTION
Dr Nicholas Braithwaite (Module chair) Phil Ashby (Producer, BBC)
Dr Lyndon Edwards (Module chair) Gerald Copp (Editor)
Mark Endean (Module chair) Debbie Crouch (Designer)
Dr Andrew Greasley Alison George (Illustrator)
Dr Peter Lewis Andy Harding (Course
Professor Charles Newey (Course and manager)
module chair) Allan Jones (Editor)
Professor Nick Reid Carol Russell (Editor)
Ken Reynolds Ernie Taylor (Course
Graham Weaver manager)
Dr George Weidmann (Module chair) Pam Taylor (Producer, BBC)
TECHNICAL STAFF SECRETARIES
Richard Black Tracy Bartlett
Naomi Williams Lisa Emmington
Angelina Palmiero
Lesley Phelps
Anita Sargent
CONSULTANTS FOR THIS BOOK
Dr Charles May (City of London Polytechnic)
Dr Nigel Mills (Birmingham University)
Dr Jerome Way (Bristol Polytechnic)
EXTERNAL ASSESSOR
Professor Michael Ashby (Cambridge University)
Chapter 1 Products, properties,
processes and principles
In this chapter we shall explore the properties of different kinds of
material, the ways in which materials can be shaped, and the uses to
which they can be put. In the course of this exploration we shall see
something of the relationship between the internal structure of materials
and their properties. Knowledge of this relationship, and of the
processes by which materials can be shaped, is fundamental to the
design and manufacture of products, which we shall also consider. Later
chapters, and other books in this series, will develop these themes more
extensively.
11 The role of materials
The materials we are concerned with begin as physical resources in or
on the Earth. They occur as gases, as liquids (especially water and oil),
as inorganic solids (minerals) and as organic solids both dead (coal for
example) and alive (wood for example). Thousands of these raw
materials are used in making the myriad products to meet our needs
(and wants) of food, shelter, communication, medicine, entertainment
and so on. We are concerned in this book with the materials from
which these artefacts are made. They are usually called engineering
materials, that is materials designed, made and used for a practical
purpose — carrying mechanical loads, electric currents, providing
thermal insulation, resisting corrosion or whatever.
raw materials basic materials engineering materials
metals, single
extract, refine, chemicals, r crystals, alloys,^
process paper, cement, process -*>{ ceramics, plastics, )
fibres composites
4 6
5 7
mine 2
drill recycle manufacture
harvest 13 8
ore oil wood
performance,
dispose
service, use
12
10
&
Figure 1.1 'Life-cycle' of engineering materials
11
Figure 1.1 puts a global perspective on the life-cycle of engineering
materials: a short manufacturing cycle links into a very long geological
one within the Earth. The symbols used are conventional in diagrams of
this and related types. The ovals (or circles) represent states, in this
diagram states of a material. The rectangles are processes, and arrows
indicate flows. The diagram is in a highly generalized form and the
details of processes and states differ from one material to another. For
instance, notice that the recycling of waste products offers a short-cut in
the cycle. Recycling is used extensively for some materials — about 60%
of lead is recycled for example and up to 30% of a glass bottle comes
from old broken glass — but, at present, there is very little recycling of
plastics and none at all for some other materials such as concrete. (See
▼Recycling and re-using A.)
T Recycling and re-usîng A
The term recycling is often used loosely.
Strictly, it means feeding waste material
(scrap) back into the same processing cycle
D
— the product is of the same quality as aluminium from smelter
(·
the original. Making glass bottles from old
ones and using old car bodies in aluminium
steelmaking are examples. This is different loss as fumes
from re-using scrap that is degraded to melting
make some other, less demanding,
product; for example, re-using old
newspapers for cardboard and old
concrete for road foundations. casting
Two sorts of scrap may be recycled or
ingot
re-used: products at the end of their useful
life (called old scrap) and waste material,
rolling
such as rejects and swarf from machining,
produced during manufacture (new scrap). old sheet new
Figure 1.2 illustrates the distinction scrap scrap
between old and new scrap in the context
can making
of aluminium drinks cans.
The cost of materials to a manufacturer is
usually the largest element in the overall
cost of a product. This is true of products brewery
as varied as aeroengines, concrete building
blocks^ and shoes and garments (where filled cans
traditionally labour has been the greatest
cost). There is thus a strong financial selling and drinking
incentive to recycle and re-use materials.
empty cans
Why isn't recycling of old scrap more
prevalent?
discard
Cost and technical feasibility. Scrap
usually consists of blended or combined
materials from which the original
ingredients cannot easily be recovered. For C land fill j
a manufacturer, recycling is only justified
if the cost of collecting scrap and
separating out the required material is less Figure 1.2 Recycling of scrap in
than the cost of new starting materials. manufacture of aluminium cans
12
In the early stages of human existence, technological, activity was
limited to the naturally occurring materials to hand: wood, bone, hide,
natural fibres, stone, flint and so on. Even then, the raw materials were
usually manipulated in some way to make them more suitable for
particular uses, albeit by simple processes such as drying and chipping.
Figure 1.3 shows some examples. Some of the rudiments of shaping
were obviously appreciated, especially the importance of the relative
hardness of materials for chipping and grinding — a very hard material
would be needed to form the boring tool. (See ▼ Assessing hardness A.)
(c)
Figure 1.3 Neolithic artefacts, about
3000BC. (a) Flint boring tool.
(b) Ceremonial stone hammer head.
(c) Bone needle (approx. 10 cm long).
Courtesy of the National Museums of
Scotland
T Assessing hardness A
A hard material is difficult to scratch, wear most common test is the Vickers hardness constant force
away by abrasion or to indent. Hardness test. A diamond indenter, in the form of a
is not a fundamental property of a square pyramid with an included face
material: for each method of measuring it, angle of 136°, is pushed with constant diamond
it is some combination of elastic, plastic, force into the surface of a sample (Figure indenter
and (in some cases) fracture properties. 1.4a). The resulting 'square' impression
Hardness can be measured only by (Figure 1.4b) is viewed in a measuring
comparison with a material used as a microscope and the two diagonals
scratcher or indenter and has objective measured.
meaning only in terms of a specific type
The hardness is given a number H which
of test. For example, glass will scratch v
is calculated as the load (in kg) on the
steel but fractures more readily under
indenter divided by the area of the faces
indentation; nylon has a high resistance to
of the indentation. Most hardness testing
wear but not to indentation.
machines have a set of tables from which,
The first systematic hardness scale was having determined the average of the two
proposed by Mohs in 1822. Ten standard diagonals of the 'indent', the user can read
minerals, ranging in hardness from talc to off the Vickers hardness number.
diamond, were used as the reference scale.
The Vickers test is more common than the
The hardness of a material under test was H D H
earlier Brinell test (BH), which uses a steel
determined by which of the reference
ball as the indenter. Another test, the
minerals could scratch the material. The Figure 1.4 Vickers hardness test
Rockwell, uses different loads with a
scale was not very sensitive to different
diamond indenter for hard materials and a
degrees of hardness.
range of steel balls for softer materials.
Nowadays hardness is usually measured in
terms of resistance to indentation, and the
13
Nowadays most of the materials we use are artificial, and many more
processes are available for manipulating and shaping them. Of course,
some naturally occurring materials are still used in relatively unchanged
form — timber in furniture and stone in buildings for instance — but
really only for simple functions. In their original state, these materials
are not able to meet other, more demanding functions. On the other
hand, the engineering materials used in the artefacts that provide our
vastly improved living conditions are purpose made. For artefacts as
simple as paperclips, pens, and window panes, let alone those as
complex as computers, satellites and nuclear power stations, raw
materials are refined, combined and processed into engineering materials
with utterly different, or vastly improved, characteristics. Polyethylene
kitchen utensils don't look a bit like the crude oil from whence they
came, and the highly pure and perfect single crystals used in silicon
chips (Figure 1.5) have come a long way from grains of sand. ▼ Silicon
single crystals ▲ gives a brief summary of how silicon electronic
Figure 1.5 Courtesy of Philips
devices are made.
Components Ltd
T Silicon single crystals,
The starting material for a device is a (Si0 ), which is reduced to silicon rather
2
wafer — a flat disc cut from a single as iron oxide is reduced to iron. The
crystal rather as slices are cut from a product contains about 98% silicon.
salami sausage (Figure 1.7). An array of Further elaborate purification procedures
devices is built onto and into the surface are necessary before it is adequate for
of the wafer by a combination of electronic use.
oxidation, masking, etching and
A common way of producing a single
deposition of other elements. The wafer is
crystal is the Czochralski technique,
then cut into a number of chips (typically
shown in Figure 1.8. A small single crystal
250).
of silicon is used as a 'seed' on which to
Silicon single crystals begin as silica grow a large crystal (up to 25 cm in
Figure 1.6 (a) Crystal, (b) Glass (or
diameter). It is held in a water-cooled
amorphous) solid
chuck and lowered into the molten silicon.
In simple terms, solids can be crystalline, When the temperature is just right for the
glassy or a mixture of the two. Figure 1.6 seed to grow, it is slowly rotated and
illustrates the difference. The glass in withdrawn.
Figure 1.6(b) lacks the long-range order of pull
the crystal in Figure 1.6(a) — compare the
line AB passing through the centres of CL_lT^ crystal rotation
some atoms in the crystal with AB' for -seed
the glass. Notice that the glass has
short-range order in that it consists of
similar small clusters — in this case
three-atom clusters.
Silicon can be made in either a crystalline
or an amorphous form. Crystalline silicon
is the basis of most electronic devices such
as transistors, diodes and integrated
circuits. Such devices put stringent
requirements on the material from which Figure 1.7 Polished silicon wafer, courtesy
they are made. In particular, they usually of Monsanto Electronic Materials
heater crucible rotation
have to be single crystals, that is, a Company. For electronic devices, the
crystalline solid in which the long-range wafer must be of the highest possible Figure 1.8 Growing a single crystal of
order extends throughout its volume. quality silicon
14