Refractory Metal Alloys Metallurgy and Technology: Proceedings of a Symposium on Metallurgy and Technology of Refractory Metals held in Washington, D.C., April 25–26, 1968. Sponsored by the Refractory Metals Committee, Institute of Metals Division, The Me

492 Pages·1968·7.85 MB·English

by  B. A. Wilcox (auth.)

REFRACTORY METAL ALLOYS
Metallurgy and Technology
Editors
I. Machlin
Materials and Processes Branch
Naval Air Systems Command
Departrn.ent of the Navy
Washington, D.C.
R. T. Begley
Astronuclear Laboratory
Westinghouse Electric Company
Pittsburgh, Pennsylvania
atnd
E. D. Weisert
Materials Research
Rocketdyne Division
North American Rockwell CompOh/,y
Canoga Park, California
•
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A Publication of The Metallurgical Society of AIME
REFRACTORY
METAL ALLOYS
Metallurgy and Technology
Proceedings of a Symposium on Metallurgy and Tech
nology of Refractory Metals held in Washington, D.C.,
April 25-26, 1968. Sponsored by the Refractory Metals
Committee, Institute of Metals Division, The Metallurgi
cal Society of AIME and the National Aeronautics and
Space Administration, Washington, D.C.
<±>
PLENUM PRESS • NEW YORK • 1968
ISBN 978-1-4684-9122-7 ISBN 978-1-4684-9120-3 (eBook)
001 10.1007/978-1-4684-9120-3
© 1968 American Institute of
Mining, Metallurgical, and Petroleum Engineers, Inc.
Softcover reprint of the hardcover I st edition 1968
Library of Congress Catalog Card Number 69-13684
Plenum Press is a division of
Plenum Publishing Corporation
227 West 17 Street, New York, N. Y.10011
Preface
This publication documents Proceedings of the Symposium on Metal
lurgy and Technology of Refractory Metal Alloys, held in Washington, D.C.
at the Washington Hilton Hotel on April 25-26, 1968, under sponsorship of
the Refractory Metals Committee, Institute of Metals Division, of the
Metallurgical Society of AIME, and the National Aeronautics and Space
Administration. The Symposium presented critical reviews of selected
topics in refractory metal alloys, thereby contributing to an in-depth
understanding of the state-of-the-art, and establishing a base line for
further research, development, and application.
This Symposium is fifth in a series of conferences on refractory
metals, sponsored by the Metallurgical Society of AlME. Publications
issuing from the conferences are valuable technical and historical source
books, tracing the evolution of refractory metals from early laboratory
alloying studies to their present status as useful engineering materials.
Refractory metals are arbitrarily defined by melting point. A
melting temperature of over 35000F was selected as the minimum for this
Symposium, thus excluding chromium and vanadium, which logically could be
treated with other refractory metals in Groups VA and VIA of the periodic
table. The Refractory Metals Committee is planning reviews of chromium
and vanadium in subsequent conferences.
Of eleven metals with melting points above 35000F, four have been
advanced significantly in recent years, as bases for structural alloys,
namely Cb, Mo, Ta, and W. The remaining seven (Re, 8f, Ir, Rh, Ru, Tc
and Os) have received lesser development, a fact reflected in the Sympo
sium program. Perhaps future Symposia will show a different emphasis.
At the time of the first High Temperature Materials Conference in
1957 (Cleveland, Ohio) only the Mo-O.5% T1 alloy was in commercial pro
duction. Currently (1968) several dozen useful Cb, Mo, Ta, and W alloys
have evolved, with many obtainable in good quality as sheet, foil, tube,
wire, bar, and forgings. Although complete information on aerospace,
nuclear, and commercial applications was not available for presentation
at the SympoSium, it appears that refractory metals are serving essential
structural functions, predominantly in prototype studies of propulsion,
power generation, and hypersonic flight devices, with few requirements
involving large quantities.
A major factor limiting the utility of refractory metals in high
temperature processes continues to be the lack of alloys (coated or
otherwise) reliably operable for long times (multi-hundreds ofbours) in
oxidizing environments. Nonetheless, there are several environments in
which refractory metals are optimum materials, including vacua, inert
gases, and liquid alkali metals. In oxidizing environments coated re
frac~ory metals can serve for limited periods, under appropriate con-
v
vi PREFACE
ditions.
The U. S. capability in refractory metals for structural uses has
been attained with Government support. supplemented by industry. of pro
grams ranging from basic research to fabrication of hardware. Much work
remains. if desired improvements in oxidation-resistance. strength.
ductility. weldability and fabricability are to be attained. However, it
appears likely that research efforts. in the future, will be selectively
directed towards solving those critical problems limiting the useful
potential of refractory metals. The invited papers in this publication
were intended to provide maximum information required in judging future
needs and research directions.
We are grateful to the National Aeronautics and Space Administration
for support enabling us to publish these proceedings. Much credit is due
to authors of papers, who have made significant professional contributions
by directing many hours of their leisure time to hard work. Our thanks
are also extended to session chairmen and to members of the Refractory
Metals Committee. who partiCipated in organizing this Symposium.
Distribution of this book in a timely and economical manner has been
facilitated by photographic reproduction of authors' manuscripts, a pro
cedure necessitating some relaxation of standards for editorial uniformity
and format. We trust that the advantage of timely publication will out
weigh perfection of format. It is regretted that the following planned
papers were not available: Refractory Metals in Aerospace Structures, Use
of Refractory Metals in Aerospace PropulSion, and Molybdenum and Moly
bdenum-Base-Alloys-Recent Developments.
April 1968 1. Hachlin
R. T. Begley
E. D. Weisert
Contents
Basic Strengthening Mechanism in Refractory Metals ••••••••••••••• 1
B. A. Wilcox
High Temperature Creep and Fracture Behavior of the
Refractory Metals 41
0.0 •• 00000 •• 0.0000000.00000.0.0000 ••• 00
R. T. Begley, D. L. Harrod, and R. E. Gold
The Effect of Thermal-Mechanical Treatments on the Structure
and Properties of Refractory Metals ••••••••••••••••••••• 85
R. A. Perkins
Interactions in Coated Refractory Metal Systems ~................. 121
A. G. Metcalfe and A. R. Stetson
Interactions of Refractory Metals with Active Gases in
Vacua and Inert Gas Environments •••••••••••••••••••••••• 165
H. Inouye
Hydrogen Effects in Refractory Metals 197
W. T. Chandler and R. J. Walter
The Compatibility of Refractory Metals with Liquid Metals •••••••• 251
E. E. Hoffman and R. W. Harrison
Refractory Metals in Space Electric Power Conversion Systems ••••• 289
J. W. Semmel, Jr.
Recent Advances in Columbium Alloys 325
R. G. Frank
Considerations in the Development of Tantalum Base Alloys •••••••• 373
R. W. Buckman, Jr. and R. C. Goodspeed
Advanced Processing Technology and High Temperature Mechanical
Properties of Tungsten Base Alloys ••••••••••••••••••••• 395
H. G. Sell
vii
viii CONTENTS
The Less Common Refractory Metals (Rhenium, Technetium,
Hafnium, Noble Metals) ••••••••••••••••••••••••••••••••••• 451
J. Maltz
Index 489
0 0 •• " 0 •••••• 0 • 0 " ••••• " • 0 0 • " 0 • 0 •• " 0 0 " 0 • 0 0 " •••• 0 0 0 0 •••• 0 0 " 0 •• 0
BASIC STRENGTHENING MECHANISMS
IN REFRACTORY METALS
B. A. Wilcox
ABSTRAcr
Various mechanisms of strengthening refractory metals and
alloys are discussed. Special emphasis is placed on the microstructural
features which can be varied to produce strengthening, and relevant
illustrations are given. The general areas reviewed include: (a)
strengthening by second phase particles, (b) solid solution strength
ening, (c) strain hardening and grain size refinement, (d) retaining
worked structures at high temperatures, (e) dynamic strengthening, and
(f) fiber reinforcement.
B. A. Wilcox is a Fellow in the Metal Science Group, Battelle Memorial
Institute, Columbus Laboratories, Columbus, Ohio.
1
2 B. A.WILCOX
INTRODUCTION
In order to capitalize fully on the potential of refractory
metals in structural applications, it is necessary to strengthen the base
metals. Thus, improving the strength of refractory metals has been one
of the most important topics of research and development on these mate
rials, and in previous AIME Refractory Metals Symposia this area has
been the subject of major review papers (1,2).
This paper approaches strengthening in refractory metals by
considering the various mechanisms that have been employed to increase
the yield, ultimate and creep strengths. The subjects treated are:
(a) strengthening by second phase particles, (b) solid solution
strengthening, (c) strain hardening and grain size refinement, (d)
retaining worked structures at high temperatures, (e) dynamic
strengthening, and (f) fiber reinforcement. Radiation hardening is a
special topic which is not considered here, since it is not a technique
that materials designers intentionally use to strengthen refractory
metals. Also, texture strengthening is not discussed, because in the
major refractory metals (W, Mo, Cr, Ta, Nb, V) the BCC structure is not
amenable to pronounced strengthening by preferred orientation, as com~
pared to HCP metals.
The main emphasis here is placed on strengthening at room and
elevated temperatures. Many of the strengthening mechanisms, e.g.,
dispersion hardening, solution strengthening, working and grain size
refinement, etc., also are operative at low temperatures. However, at
low temperatures additional factors, such as overcoming the Peierls
barrier, are important. Conrad (3) has reviewed this area including
numerous results on the BCC refractory metals. For practical purposes,
ductility as well as strength is important to consider in refractory
metal alloy development. In many cases those factors which influence
the strength of refractory metals also affect the fracture behavior.
However, this topic is not treated here, since it has been well re
viewed in several recent papers (4,5).
A complete review of the literature on refractory metal
strengthening is beyond the scope of this paper. Rather, the author
has tried to give details of pertinent strengthening mechanisms, and
to illustrate these with appropriate examples based on refractory metal
alloys. Thus, it is the intention of this paper to provide the alloy
developer with basic guidelines which will be of assistance in selecting
methods to improve the strength of refractory metals.
It is often desirable in practice to employ more than one
strengthening mechanism. This paper considers that the various
strengthening mechanisms can supplement one another and they are often
interrelated. Even though the strengthening effects may not be directly
additive, it is convenient to formulate a phenomenological expression
such that the strength, cr, of an alloy is written as:
(1)