Table Of ContentSTRENGTHENING OF
-CERAMICS
MANUFACTURING ENGINEERING
AND MATERIALS PROCESSING
A Series of Reference Books andTextbooks
SERIES EDITORS
Geoffrey Boothroyd George E. Dieter
DepartmentofMechanicalEngineering Dean, CollegeofEngineering
UniversityofMassachusetts UniversityofMaryland
Amherst,Massachusetts CollegePark, Maryland
1. Computers in Manufacturing, U. Rembold, M. Seth, andJ.S. Weinstein
2. Cold Rolling of Steel, William L. Roberts
3. Strengthening of Ceramics: Treatments, Tests, and Design Applications,
Henry P. Kirchner
OTHERVOLUMES IN PREPARATION.
STRENGTHENING OF
CERAMICS
Treatments, Tests,
and Design Applications
Henry P. Kirchner
CeramicFinishing Company
StateCollege, Pennsylvania
MARCEL DEKKER, INC. New York and Basel
Library of Congress Cataloging in Publication Data
Kirchner, Henry Paul.
Strengthening of ceramics.
(Manufacturing engineering and materials processing 3)
Bibliography: p.
Includes index.
1. Ceramic materials. I. Title. II. Series.
TA455.C43K57 666 79-17514
ISBN 0-8247-6851-5
COPYRIGHT © 1979 by MARCEL DEKKER, INC. ALL RIGHTS RESERVED
Neither this book nor any part may be reproduced or transmitted in
any form or by any means, electronic or mechanical, including photo-
copying, microfilming, and recording, or by any information storage
and retrieval system, without permission in writing from the
publisher.
MARCEL DEKKER, INC.
270 Madison Avenue, New York, New York 10016
Current printing (last digit):
10 9 8 7 6 5 4 3 2
PRINTED IN THE UNITED STATES OF AMERICA
PREFACE
Considerable resources have been devoted to diverse attempts to
strengthen ceramic materials. In the majority of cases the results
achieved have been marginal, leading to considerable frustration.
Based on earlier success with strengthening of glass and glass-
ceramics, using approaches involving treatments to induce compressive
surface stresses, substantial progress was made in strengthening con-
ventional polycrystalline ceramics and oxide single crystals. This
monograph describes these advances. The methods described were de-
veloped, in large part, at Ceramic Finishing Company, but results
from other laboratories that have come to my attention are included.
The scope of this monograph is limited to treatments for polycrystal-
line ceramics and oxide single crystals. Despite the limited scope
it was necessary to omit much important data. This information is
available in the references.
Designers will find that, in addition to the descriptions of
individual treatments and the resulting improvements in strength,
information on potential applications, limitations of the treatments,
design considerations, and costs are presented.
The principal advantages of compressive surface layer treatments
are improved strength, decreased penetration of surface damage and
strength degradation, and improved impact, thermal shock and delayed
fracture performance. The highest strengths have, thus far, been
achieved by thermal (quenching) treatments. These treatments are
limited, to some extent, by thermal 'shock damage in the larger and
more complex shapes. Coatings, chemical treatments and treatments
to induce phase transformations are alternative processes. Although
the achievable strengths using these treatments are somewhat lower,
a much wider range of shapes and sizes can be treated.
Potential applications should be sought in the following areas:
bearings, cutting tools, gas turbines, radomes, IR domes, armor, ex-
trusion dies, pump parts, lighting envelopes, laser windows, leading
edges, other wear resistance parts, and so forth. Progress in the
iii
iv PREFACE
application of "tempered" glasses and glass-ceramics can provide some
guidance as to what to expect. It should be noted that the payoff
for improvements in many of these applications may be very large
because the ceramic part is the critical link in the operation of the
complete device. Operations of complete machines may succeed or fail
depending on the success or failure of these individual ceramic parts.
In these circumstances, substantial improvements in strength may be
essential to reliable performance.
Subcritical crack growth is the principal factor affecting the
reliable use of many ceramics in load bearing applications. The
original flaws gradually increase in size to the point that stress
intensification may cause catastrophic failure. To reduce subcriti-
cal crack growth, one can reduce the load or redesign the part so that
the stress is less. However, in many cases neither means is satis-
factory. Use of compressive surface stresses provides another alter-
native. These surface stresses, because they subtract from normal
tensile stresses in the surface where most of the severe flaws are,
reduce the stress intensity factor at flaws in stressed members,
thus decreasing the subcritical crack growth rate,
Proof testing is an accepted means for assuring the strength of
ceramic parts by removing parts weaker than a particular strength
level from the distribution. The most critical proof test parameter
is the difference between the proof test stress and the use stress.
The greater the difference can be, the greater will be the effective-
ness in removing weak parts from the lot, especially when the sub-
critical crack growth during loading and unloading from proof testing
is considered. Because the compressive surface stresses raise the
nominal stresses at which surface flaws act to cause failure, treated
specimens can be proof tested at stresses that are much higher than
otherwise possible. For a given use stress this means a larger dif-
ference between the proof stress and the use stress and therefore a
smaller probability of failure of a partin service.
More widespread use of ceramics can aid greatly in improvement
of efficiencies of energy conversion equipment and in weight reduc-
tion in aerospace applications. Improvements in energy efficiency
can occur by means such as increased inlet temperatures leading to
increased Carnot efficiencies and by reduction in the requirements
for cooling air in gas turbine engines. Weight reduction can be
accomplished by substitution of ceramics for refractory metals, re-
duction of the thickness of sections through the use of the greater
stiffness of some ceramics, and by other means. Weight reductions
in aerospace applications can be especially important because less
fuel is needed leading to still further weight reductions. The in-
creased strength and reliability of ceramics with compressive surface
stresses will aid in adapting ceramics to these applications.
It is a pleasure to acknowledge the contributions of my assoc-
iates at Ceramic Finishing Company, especially Robert M. Gruver and
others, many of whom have been coauthors of the various earlier de-
scriptions of this work, and the many research workers at other
organizations who have contributed to our knowledge of this field.
I am also grateful to the sponsors of the research including espec-
ially the Naval Air Systems Command and the Office of Naval Research,
PREFACE
v
and the technical contract monitors, Charles F. Bersch and Arthur M.
Diness. H~lpful suggestions were made by Richard C. Bradt and
John B. Wachtman, Jr. who reviewed the original manuscript. It is
also a pleasure to acknowledge the typing done by Shirley Wittlinger
and Elaine Smile~.
Henry P. Kirchner
April, 1979
