Table Of ContentMaterials Research and Engineering
Edi ted by B. Ilschner
Volume 2
K.A. Padmanabhan . G.1. Davies
Superplasticity
Mechanical and Structural Aspects,
Environmental Effects,
Fundamentals and Applications
With 86 Figures
Springer-Verlag Berlin Heidelberg New York 1980
KUPPUSWAMY ANANTHA PADMANABHAN
Professor of Metallurgy,
Indian Institute of Technology, Madras (India)
(formerly Banaras Hindu University, Varanasi, India)
GRAEME JOHN DAVIES
Professor of Metallurgy,
University of Sheffield, Sheffield (U.K.)
Dr. rer. nat. BERNHARD ILSCHNER
o. Professor, Institut fUr Werkstoffwissenschaften der Universitat Erlangen-Niirnberg
Library of Congress Cataloging in Publication Data.
Padmanabhan, Kuppuswamy Anantha, 1945 -Superplasticity.
(Materials research and engineering; v. 2)
Bibliography: p. Includes index.
1. Superplasticity. I. Davies, G. J., joint author.
II. Title. III. Series: Materials research and engineering; v. 2.
TA418.14.P32 620.1'1233 80-13292
ISBN-13 :978-3-642-81458-7 e-ISBN-13:978-3-642-81456-3
DOl: 10.1007/978-3-642-81456-3
This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned,
specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine
or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other
than private use, a fee is payable to the publisher, the amount-ofthe fee to be determined by agreement with the publisher.
© Springer-Verlag Berlin. Heidelberg 1980
Softcovcr reprint of the hardcover 1st edition 1980
The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific
statement. that such names are exempt from the relevant protective laws and regulations and therefore free for
general use.
2362/3020 -543210
Editor's Preface
This is the second book in a new series - "Materials Research
and Engineering" - devoted to the science and technology of
materials. "Materials Research and Engineering" evolves from
a previous series on "Reine und Allgemeine Metallkunde", which
was edited by Werner KBster until his eightieth birthday in
1976.
Although the present series is an outgrowth of the earlier
one, it should not and cannot be regarded as a continuation.
There had to be a shift of scope - and a change in presenta
tion as well. Metallurgy is no longer an isolated art and
science. Rather, it is linked by its scientific basis and
technological implications to non-metallic and composite
materials, as well as to processes for production, refining,
shaping, surface treatment, and application. Thus, the new
series, "Materials Research and Engineering", will present
up-to-date information on scientific and technological pro
gress, as well as on issues of general relevance within the
engineering field and industrial society.
Following the general position analysis of materials in the
present world as given in volume 1, now volume 2 focuses on
a special topic: It provides a thorough treatment of theoretical,
experimental, and applied aspects of superplasticity.
Superplastic deformation of metals and ceramics is a phenomenon
as attractive from a fundamental as from an engineering point of
view. The unusually high ductility suggets an underlying micro
mechanical mechanism basically different from normal strain
hardening and creep; careful experiments to clarify the contribu
tions from dislocation glide, grain boundary shear, and diffu
sonalflow, respectively, are necessary.
On the other hand, the exceptional phenomenological features of
superplasticity call for practical evaluation, in particular
v
application for metal forming operations. These technological
aspects are dealt with in the present volume as well as the the
oretical basis. Thus, the book by Padmanabhan and Davies promises
to present up-to-date, precise, comprehensive and interesting in
formation to both scientists and engineers.
Erlangen, Germany, January 1980 Bernhard Ilschner
VI
Author's Preface
SUperplasticity in metals and alloys is a phenomenon which
by its very uniqueness has attracted the attention of scientists and
technologists over a considerable number of years. The earliest obser
vations were made in the 1920's but little development followed from
them at that stage. There was a resurgence of interest in the mid
1940's in Russia but the extensive research activity of recent times
was stimulated by the published researches of W.A.Backofen and his
co-workers at M.I.T. beginning about 1964. The subj~ct is now one
of interest to materials scientists, metallurgists, physicists and
engineers.
There has been a great deal of work devoted to both the funda
mental and the technological aspects of superplasticity. The under
standing of the basic mechanisms of the deformation processes involved
has been increased by theoretical and experimental efforts. On the
other hand, the application of experimental data to real problems has
not been neglected. Alloys of considerable commercial interest have
been developed and there are a number of practical forming operations
currently in use which utilise superplastic deformation.
In recent years the subject has been reviewed in part in
technical journals and an impressive number of research papers have
been published. Superplasticity is now well-established as a research
and development subject and the time seems ripe for a comprehensive
discussion of the subject.
This is the objective of this monograph. It considers the
theoretical and experimental aspects of superplasticity, together with
areas of potential or actual application. It is intended for workers
VII
in industry and in academic institutions. It will have succeeded in
its aims if research and development is stimulated or if a proper under
standing of the subject is given to those who wish such an understanding
without a direct involvement.
MADRAS, INDIA, January 1980 K.A. PADMANABHAN
SHEFFIELD, U.K., January 1980 G.J. DAVIES
VIII
Acknowledgements
The authors thank Professor B. Ilschner, Editor of this
Springer Series on Materials Research and Engineering, for his kind
invitation to write this monograph. The co-operation of Mr. M. Hofmann
of Springer Verlag at every stage is gratefully acknowledged.
Grateful acknowledgement is also made to the following organi
zations/societies and publishers for permission to reproduce illustra
tions: Academic Press, American Institute of Mining, Metallurgical and
Petroleum Engineers, American Institute of Physics, American Society for
Metals, Chapman and Hall Limited, Dr. Riederer Verlag GmbH, Elsevier
Sequoia, Illinois Institute of Technology, Pergamon Press, Pratt and
Whitney Aircraft Limited, Rockwell International Limited, The Metallur
gical Society of A.I.M.E., The Metals Society, The Royal Society, T.I.
Superform Limited and University of California Press.
Professor G.W. Greenwood, Dr. P.M. Hazzledine and Dr. P.J.
Wray have also kindly given their consent for the inclusion of illus
trations from their articles.
One of the authors (KAP) wishes to thank in addition the
following people: Professor T.R. Anantharaman whose gentle care and
constant encouragement made book-writing a pleasure; Mrs. Gita Padmana
bhan but for whose assistance and understanding at every stage this
monograph could not have been completed; Professor S. Ranganathan for
valuable discussions on the structure of high-angle grain boundaries;
Professor P. Rama Rao, who as the senior-most member of the mechanical
metallurgy group at Banaras Hindu University, was generous with his help
throughout the author's stay at that University.
Thanks are due to Dr. L.R. Vaidyanath, Director, Indian Copper
Information Centre, for providing office facilities for the production
of the manuscript in a form suitable for photo-offset printing. Finan
cial support for acquiring secretarial assistance was given by the
Aeronautics Research & Development Board, Ministry of Defence, Govern
ment of India.
IX
'!'he trillionth part has not been said;
II
and all that has been said but multiplies
the avenues to what remains to be said.
II
Herman Melville
x
Contents
1. HISTORICAL INTRODUCTION 1
1.1 First Observations of Structural Superplasticity 1
1.2 Early Observations of Environmental Superplasticity 4
1.3 The Revival of Interest in Structural SUperplasticity 5
2. THE HECHANICS OF SUPERPLASTIC DEFORNATION AND THE ASSESSNENT
OF SUPERPLASTIC BEHAVIOUR 8
2.1 The Tensile Test 8
2.2 Constitutive Relations for Superplastic ~~terials 9
2.3 The Deformation Behaviour of SUperplastic r·laterials 12
2.3.1 The tensile stress-strain curve 12
2.3.2 Tensile stress-strain rate variations 15
2.3.3 Compressive behaviour 16
2.3.4 Torsion testing 16
2.4 The Shape of the Deforming Specimen 17
2.5 Plastic Instability 19
2.5.1 The onset of necking 19
2.5.2 The geometry of neck formation 23
2.6 The Elongations of Rate-Sensitive Materials 25
2.7 The Strain-rate sensitivity Index, m 29
2.7.1 Determination of m from the <T"t - Et curve 29
2.7.2 Determination of m using change in strain
rate method 30
2.7.3 Determination of m from stress-relaxation tests 34
2.7.4 Comparison of m values determined using diffe
rent techniques 35
2.7.5 The physical significance of m value measure
ments 37
2.8 strain-rate sensitivity in Environmentally Superplastic
Materials 38
2.9 Other Test Procedures for studying structural Super
plasticity 40
XI
