Engineering materials 2: an introduction to microstructures, processing, and design

392 Pages·1998·11.495 MB·English

by  D R H Jones, Michael F. Ashby

Engineering Materials 2
An Introduction to Microstructures, Processing and Design

Engineering Materials 2
An Introduction to Microstructures, Processing and Design
Second Edition
by
Michael F. Ashby
and
David R. H. Jones
Department of Engineering, Cambridge University, England
OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI
Butterworth-Heinemann
Linacre House, Jordan Hill, Oxford OX2 8DP
225 Wildwood Avenue, Woburn, MA 01801-2041
A division of Reed Educational and Professional Publishing Ltd
A member of the Reed Elsevier plc group
First edition 1986
Reprinted with corrections 1988
Reprinted 1989, 1992
Second edition 1998
Reprinted 1999
© Michael F. Ashby and David R. H. Jones 1998
All rights reserved. No part of this publication
may be reproduced in any material form (including
photocopying or storing in any medium by electronic
means and whether or not transiently or incidentally
to some other use of this publication) without the
written permission of the copyright holder except
in accordance with the provisions of the Copyright,
Designs and Patents Act 1988 or under the terms of a
licence issued by the Copyright Licensing Agency Ltd,
90 Tottenham Court Road, London, England W1P 9HE.
Applications for the copyright holder’s written permission
to reproduce any part of this publication should be addressed
to the publishers
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Cataloguing in Publication Data
A catalogue record for this book is available from the Library of Congress
ISBN 0 7506 4019 7
Printed and bound in Great Britain by
Biddles Ltd, Guildford and Kingd’s Lynn
Contents
General introduction ix
A. Metals
1. Metals 3
the generic metals and alloys; iron-based, copper-based, nickel-based,
aluminium-based and titanium-based alloys; design data
2. Metal structures 14
the range of metal structures that can be altered to get different
properties: crystal and glass structure, structures of solutions and
compounds, grain and phase boundaries, equilibrium shapes of
grains and phases
3. Equilibrium constitution and phase diagrams 25
how mixing elements to make an alloy can change their structure;
examples: the lead–tin, copper–nickel and copper–zinc alloy systems
4. Case studies in phase diagrams 34
choosing soft solders; pure silicon for microchips; making bubble-free ice
5. The driving force for structural change 46
the work done during a structural change gives the driving force for the
change; examples: solidification, solid-state phase changes, precipitate
coarsening, grain growth, recrystallisation; sizes of driving forces
6. Kinetics of structural change: I – diffusive transformations 57
why transformation rates peak – the opposing claims of driving force
and thermal activation; why latent heat and diffusion slow
transformations down
7. Kinetics of structural change: II – nucleation 68
how new phases nucleate in liquids and solids; why nucleation is helped
by solid catalysts; examples: nucleation in plants, vapour trails, bubble
chambers and caramel
vi Contents
8. Kinetics of structural change: III – displacive transformations 76
how we can avoid diffusive transformations by rapid cooling; the
alternative – displacive (shear) transformations at the speed of sound
9. Case studies in phase transformations 89
artificial rain-making; fine-grained castings; single crystals for
semiconductors; amorphous metals
10. The light alloys 100
where they score over steels; how they can be made stronger: solution,
age and work hardening; thermal stability
11. Steels: I – carbon steels 113
structures produced by diffusive changes; structures produced by
displacive changes (martensite); why quenching and tempering can
transform the strength of steels; the TTT diagram
12. Steels: II – alloy steels 125
adding other elements gives hardenability (ease of martensite formation),
solution strengthening, precipitation strengthening, corrosion resistance,
and austenitic (f.c.c.) steels
13. Case studies in steels 133
metallurgical detective work after a boiler explosion; welding steels
together safely; the case of the broken hammer
14. Production, forming and joining of metals 143
processing routes for metals; casting; plastic working; control of grain
size; machining; joining; surface engineering
B. Ceramics and glasses
15. Ceramics and glasses 161
the generic ceramics and glasses: glasses, vitreous ceramics, high-
technology ceramics, cements and concretes, natural ceramics (rocks and
ice), ceramic composites; design data
16. Structure of ceramics 167
crystalline ceramics; glassy ceramics; ceramic alloys; ceramic micro-
structures: pure, vitreous and composite
17. The mechanical properties of ceramics 177
high stiffness and hardness; poor toughness and thermal shock
resistance; the excellent creep resistance of refractory ceramics
Contents vii
18. The statistics of brittle fracture and case study 185
how the distribution of flaw sizes gives a dispersion of strength: the
Weibull distribution; why the strength falls with time (static fatigue);
case study: the design of pressure windows
19. Production, forming and joining of ceramics 194
processing routes for ceramics; making and pressing powders to shape;
working glasses; making high-technology ceramics; joining ceramics;
applications of high-performance ceramics
20. Special topic: cements and concretes 207
historical background; cement chemistry; setting and hardening of
cement; strength of cement and concrete; high-strength cements
C. Polymers and composites
21. Polymers 219
the generic polymers: thermoplastics, thermosets, elastomers, natural
polymers; design data
22. The structure of polymers 228
giant molecules and their architecture; molecular packing: amorphous
or crystalline?
23. Mechanical behaviour of polymers 238
how the modulus and strength depend on temperature and time
24. Production, forming and joining of polymers 254
making giant molecules by polymerisation; polymer “alloys”; forming
and joining polymers
25. Composites: fibrous, particulate and foamed 263
how adding fibres or particles to polymers can improve their stiffness,
strength and toughness; why foams are good for absorbing energy
26. Special topic: wood 277
one of nature’s most successful composite materials
D. Designing with metals, ceramics, polymers and composites
27. Design with materials 289
the design-limiting properties of metals, ceramics, polymers and composites;
design methodology
viii Contents
28. Case studies in design 296
1. Designing with metals: conveyor drums for an iron ore terminal 296
2. Designing with ceramics: ice forces on offshore structures 303
3. Designing with polymers: a plastic wheel 308
4. Designing with composites: materials for violin bodies 312
Appendix 1 Teaching yourself phase diagrams 320
Appendix 2 Symbols and formulae 370
Index 377
General introduction
Materials are evolving today faster than at any time in history. Industrial nations
regard the development of new and improved materials as an “underpinning tech-
nology” – one which can stimulate innovation in all branches of engineering, making
possible new designs for structures, appliances, engines, electrical and electronic de-
vices, processing and energy conservation equipment, and much more. Many of these
nations have promoted government-backed initiatives to promote the development
and exploitation of new materials: their lists generally include “high-performance”
composites, new engineering ceramics, high-strength polymers, glassy metals, and
new high-temperature alloys for gas turbines. These initiatives are now being felt
throughout engineering, and have already stimulated design of a new and innovative
range of consumer products.
So the engineer must be more aware of materials and their potential than ever
before. Innovation, often, takes the form of replacing a component made of one mater-
ial (a metal, say) with one made of another (a polymer, perhaps), and then redesigning
the product to exploit, to the maximum, the potential offered by the change. The
engineer must compare and weigh the properties of competing materials with pre-
cision: the balance, often, is a delicate one. It involves an understanding of the basic
properties of materials; of how these are controlled by processing; of how materials
are formed, joined and finished; and of the chain of reasoning that leads to a successful
choice.
This book aims to provide this understanding. It complements our other book on
the properties and applications of engineering materials,* but it is not necessary to
have read that to understand this. In it, we group materials into four classes: Metals,
Ceramics, Polymers and Composites, and we examine each in turn. In any one class
there are common underlying structural features (the long-chain molecules in poly-
mers, the intrinsic brittleness of ceramics, or the mixed materials of composites) which,
ultimately, determine the strengths and weaknesses (the “design-limiting” properties)
of each in the engineering context.
And so, as you can see from the Contents list, the chapters are arranged in groups,
with a group of chapters to describe each of the four classes of materials. In each group
we first introduce the major families of materials that go to make up each materials
class. We then outline the main microstructural features of the class, and show how
to process or treat them to get the structures (really, in the end, the properties) that
we want. Each group of chapters is illustrated by Case Studies designed to help you
*M. F. Ashby and D. R. H. Jones, Engineering Materials 1: An Introduction to their Properties and Applications,
2nd edition, Butterworth-Heinemann, 1996.
x General introduction
understand the basic material. And finally we look at the role of materials in the
design of engineering devices, mechanisms or structures, and develop a methodology
for materials selection. One subject – Phase Diagrams – can be heavy going. We have
tried to overcome this by giving a short programmed-learning course on phase dia-
grams. If you work through this when you come to the chapter on phase diagrams you
will know all you need to about the subject. It will take you about 4 hours.
At the end of each chapter you will find a set of problems: try to do them while the
topic is still fresh in your mind – in this way you will be able to consolidate, and
develop, your ideas as you go along.
To the lecturer
This book has been written as a second-level course for engineering students. It pro-
vides a concise introduction to the microstructures and processing of materials (metals,
ceramics, polymers and composites) and shows how these are related to the properties
required in engineering design. It is designed to follow on from our first-level text on
the properties and applications of engineering materials,* but it is completely self-
contained and can be used by itself.
Each chapter is designed to provide the content of a 50-minute lecture. Each block
of four or so chapters is backed up by a set of Case Studies, which illustrate and con-
solidate the material they contain. There are special sections on design, and on such
materials as wood, cement and concrete. And there are problems for the student at the
end of each chapter for which worked solutions can be obtained separately, from the
publisher. In order to ease the teaching of phase diagrams (often a difficult topic for
engineering students) we have included a programmed-learning text which has proved
helpful for our own students.
We have tried to present the material in an uncomplicated way, and to make the
examples entertaining, while establishing basic physical concepts and their application
to materials processing. We found that the best way to do this was to identify a small
set of “generic” materials of each class (of metals, of ceramics, etc.) which broadly
typified the class, and to base the development on these; they provide the pegs on
which the discussion and examples are hung. But the lecturer who wishes to draw
other materials into the discussion should not find this difficult.
Acknowledgements
We wish to thank Prof. G. A. Chadwick for permission to reprint Fig. A1.34 (p. 340)
and K. J. Pascoe and Van Nostrand Reinhold Co. for permission to reprint Fig. A1.41
(p. 344).
*M. F. Ashby and D. R. H. Jones, Engineering Materials 1: An Introduction to their Properties and Applications,
2nd edition, Butterworth-Heinemann, 1996.