The 1976 Campbell Memorial Lecture
The American Society for Metals
Intermetallic Compounds"
Their Past and Promise
J.H. WESTBROOK
rm~,;
~:
This r e v i e w s e r v e s to call attention to intermetallic compounds as a c l a s s ot materials
of great practical importance in both ancient and modern t i m e s and as a fascinating topic
of scientific inquiry. Exploration of the relevant metallurgical history illustrates the
p r o c e s s e s by which both ideas and practical developments evolve and e m p h a s i z e s that
s o m e of the threads may be traced back v e r y far in time. Three general conclusions are
drawn from the review: a) The intrinsic properties of intermetallic compounds are truly
unique and at present l e v e l s of understanding are not predictable from the fundamental
p a r a m e t e r s of the constituent atoms, b) Successful applications of i n t e r m e t a l l i c s do not
result from the m e r e knowledge of their composition, crystal structure, and intrinsic
properties but require as well a skillful and understanding control of their p r o c e s s i n g .
c) There is desirably and n e c e s s a r i l y a strong interplay between s c i e n c e and technology
in the development of the intermetallic field. The technological opportunity forecast by
s o m e unique property m e a s u r e m e n t s stimulates further related scientific investigation.
Conversely scientific advances, both those specific to i n t e r m e t a l l i c s and those pertinent
to metallurgy more generally, facilitate the rate of reduction to practice of e m p i r i c a l
discoveries.
Future trends seen in the further development of i n t e r m e t a l l i c s are: greater appreciation and control of subgrain structure, investigation of compounds of metastable structure, study of compounds with complex chemistry, the use of i n t e r m e t a l l i c s in composites,
and new insights to be drawn from data compilations such as NMR and EDS.
The Edward DeMille Campbell Memorial Lecture was established in 1926 as an
annual lecture in memory o f and in recognition o f the outstandmg scmntific conmbutions to the metallurgical profession by a distinguished educator who was
blind for all but two years o f his professional life It recognizes demonstrated
ability in metallurgical science and engineering.
J. H. WESTBROOK recewed has Doctor of Science degree in metallurgy in
1949 from Massachusetts Institute of Technology, has MS in metallurgmal engineering from Rensselaer Polytechnic Institute (1947) and his BS m metallurgical
engineering from Rensselaer (1944).
A native of Troy, N.Y, he and his family now live in Ballston Spa, N.Y
Dr Westbrook has served In vanous research and technical posts with General
Electric since 1949 He is currently manager of Materials Information Services,
Corporate Research and Development for G.E.
Dr. Westbrook has held a number of positions in the American Society for
METALLURGICAL TRANSACTIONS A
Metals, and in 1970 was named a Fellow of the Society He is also a Fellow of the
American Institute of Chemists, of the American Ceramic Society, and AAAS.
He has been elected to Sigma X1, Tan Beta PI, and Phi Lamda Upsilon and is
recipient of the Frances Mills Turner Award (EcS), the Alfred H. Gelsler Award
(ASM), the Richard L, Temphn Award (ASTM) and IS the coreciplent of the New
England Regional Conference Award (AIME)
Dr. Westbrook is also coreclplent of the Hofmann Prize (LDA) and has received an award from the New England Section of the American Ceramic Society
for "significant achaevement in ceramics."
He has published seventy technical articles on the structure and properties of
metals and ceramics and has served as editor on seven publications, including
ASM's Reprint Series, Metallurgical Classics. He was a member of the original Joint
Commission for Metallurgical Transactions. He holds three U.S. and two foreign
patents
V O L U M E 8A, S E P T E M B E R 1 9 7 7
1327
PREFACE
TODAY
we celebrate the memory
of Edward de Mille
Campbell. Insofar as I am aware, intermetallic comp o u n d s w e r e n e v e r t h e s u b j e c t of a n y of P r o f . C a m p bell's research. However, Campbell had a continuing
i n t e r e s t i n t h e c o n s t i t u e n c y of a l l o y s y s t e m s t h r o u g h out his career; and, though blind, he " s a w " perhaps
m o r e c l e a r l y t h a n m o s t of h i s s i g h t e d c o n t e m p o r a r i e s ,
t h e t r a n s c e n d i n g i m p o r t a n c e of t h e i d e n t i t y a n d m i c r o s t r u c t u r a t d i s p o s i t i o n of p h a s e s o n t h e p r o p e r t i e s
a n d b e h a v i o r of a l l o y s y s t e m s . I n t h i s s e n s e a r e v i e w of i n t e r m e t a l l i c s a s a n i m p o r t a n t c l a s s of a l l o y
c o n s t i t u e n t p h a s e s i s a n a p p r o p r i a t e t r i b u t e to h i s
memory.
It i s a n h o n o r a n d a p r i v i l e g e to p r e s e n t t h i s 5 1 s t
C a m p b e l l L e c t u r e . I n r e v i e w i n g t h e r e c o r d of t h i s
s e r i e s of l e c t u r e s , I a m s t r u c k b y w h a t a s m a l l a n d
i n t i m a t e f r a t e r n i t y we m e t a l l u r g i s t s a r e . Of t h e f i f t y
p r i o r h o l d e r s of t h i s l e c t u r e s h i p , t h i r t y a r e o r w e r e
p e r s o n a l l y k n o w n to m e ; I h a v e w o r k e d w i t h f o u r ; a n d
t w o w e r e a m o n g m y t e a c h e r s . It i s , i n d e e d , a h u m b l i n g
a n d c h a l l e n g i n g e x p e r i e n c e to a t t e m p t to m a t c h t h e
standard set by my predecessors.
INTRODU CTION
Intermetallic compounds are widely recognized
t o d a y a s i m p o r t a n t c o n s t i t u e n t s of m a n y c o m m e r c i a l
a l l o y s a n d a f e w a s s i n g l e - p h a s e m a t e r i a l s of u n i q u e
p r a c t i c a l a p p l i c a b i l i t y . It w a s n o t a l w a y s so; t h e i r
existence as discrete constituents in alloys was not
clear until the mid-nineteenth century--despite the fact
t h a t f o r h u n d r e d s (if n o t t h o u s a n d s ) of y e a r s p r e v i o u s
alloy systems were selected and composition ranges
specified so as to secure the unusual properties certain intermetallics imparted.
F o r t h e p u r p o s e s of t h i s r e v i e w , we w i l l r e g a r d a s
i n t e r m e t a l l i c s a l l c o m p o u n d p h a s e s of t w o o r m o r e
normal metals.* These phases may be either ordered
or disordered. They may exist at discrete compositions or over an extended range. Justification for
treating these materials as a family rests not upon
chemical or structural principles but derives from
c e r t a i n c o m m o n a l i t i e s of b e h a v i o r a n d f r o m t h e f a c t
that they are individual materials whose properties
a r e n o t t o b e i n t e r p o l a t e d f r o m t h o s e of t h e i r c o n s t i t u ent metals.
W e w i l l b e g i n b y r e v i e w i n g two g r o u p s of c o m m e r cially significant alloys whose attractive properties
derive from the intermetallic compounds they contain.
T h e f i r s t s e t c o n s i s t s o f s e v e r a l i n s t a n c e s of i m portant early alloys whose phase constituency was
quite unknown to their developers and users. The
s e c o n d s e t c o m p r i s e s e x a m p l e s of m o d e r n a p p l i c a t i o n s , w h e r e n o t o n l y w a s t h e c o n s t i t u e n c y of t h e a l loy k n o w n b u t t h e p r e s e n c e of t h e i n t e r m e t a l l i c w a s
*Even thmsdefimtion is not without Its ambiguities.Where should the line be
drawn between metals and nonmetals? Compounds of metals with sulfur, nitrogen
and phosphorus we can certainly exclude while retaining those with tellurium,
antimony and germanium.What then of selenium, arsenic and slhcon compounds?
And how about those essentiallymetallic compounds of two or more metals whose
existence is stabilized by the presence of a small amount of oxygen, hydrogen,
carbon, and so forth? With an admitted sacrifice in consistency, compounds of the
latter types have been included m the present discussmn whereverJustified by the
simdarlty of their properttes to those of neighboring,more ragorously"intermetallic" compounds.
1328-VOLUME 8A, SEPTEMBER 1977
q u i t e d e l i b e r a t e l y s o u g h t f r o m t h e o n s e t of t h e d e velopment. This will then permit us to contrast the
t w o p e r i o d s a n d to i d e n t i f y k e y b u i l d i n g b l o c k s i n t h e
e v o l u t i o n of t h e p h y s i c a l m e t a l l u r g y o f i n t e r m e t a l l i c
c o m p o u n d b a s e d a l l o y s . T h e a c h i e v e m e n t of a s o p h i s t i c a t e d u n d e r s t a n d i n g of t h e s e b u i l d i n g b l o c k s h a s f a c i l i t a t e d t h e r a p i d i t y of t h e d e v e l o p m e n t of s p e c i f i c a l l o y s , e n l a r g e d t h e v a r i e t y of v a r i a b l e s u n d e r o u r c o n t r o l , a n d s t i m u l a t e d t h e r e f i n e m e n t i n t h e d e g r e e of
control practicable over these variables.
EARLY APPLICATIONS OF INTERMETALLIC
ALLOYS
Mirrors
Once man recognized the principle which produced
a n i m a g e of h i m s e l f i n a s t i l l p o o l of w a t e r , h e s o u g h t a
m e a n s of m a k i n g p o r t a b l e t h i s u s e f u l a n d s e l f - g r a t i f y i n g
p h e n o m e n o n . T h e e a r l i e s t m i r r o r s w e r e of o b sidian or similar stones which took a good polish
but these were later replaced by gold or silver once
t h e m e t a l l u r g i c a r t s h a d b e e n a t t a i n e d . M i r r o r s of
bronze became the work-a-day product; examples
h a v e b e e n d a t e d a s e a r l y a s 1800 B.C.1 H o w e v e r , t h e
h i g h t i n b r o n z e s (20 to 50 w t p c t Sn) w e r e f o u n d , p a r ticularly by the Han dynasty Chinese 2 and the Romans*,
t o c o m b i n e c a s t a b i l i t y w i t h h i g h h a r d n e s s , good c o l o r ,
a n d h i g h r e f l e c t i v e p o w e r . (See F i g . 1) S u c h a l l o y s a s
c a s t i n t o m i r r o r b l a n k s ~ $ c o n s i s t e d p r i n c i p a l l y of
5 CuSn and other neighboring intermetallics. 82 This
g e n e r a l t y p e of a l l o y b e c a m e k n o w n a s " s p e c u l u m "
b e c a u s e of i t s p r i n c i p a l a p p l i c a t i o n . T h e 31.7 wt p c t
tin composition ultimately became the preferred, the
contention being that higher copper content gave too
yellow a color, higher tin, too blueP
B r o n z e m i r r o r s of t h e s o r t d e s c r i b e d w e r e t h e
s t a n d a r d p r o d u c t f o r t h o u s a n d s of y e a r s , y e t w h e n a
better product was devised, curiously this too was
based on another intermetallic compound. 1 Metallic
mirrors had been limited in market and application
b e c a u s e of t h e i r p r o h i b i t i v e w e i g h t a n d c o s t i n l a r g e
sizes. The Venetians by the fifteenth century had perf e c t e d m e a n s of p r o d u c i n g l a r g e f l a t g l a s s p l a t e s .
Meanwhile, an unknown artisan in France or Germany
h a d d e v i s e d a m e a n s of a m a l g a m a t i n g t i n a n d a p p l y i n g
i t t o g l a s s to f o r m a m i r r o r s u r f a c e w A b o u t 1505 A . D .
two Venetian brothers, Andrea and Domenico del
Gallo, obtained from craftsmen in Flanders the rights
t o t h e t i n - m e r c u r y p r o c e s s of m i r r o r m a k i n g , r i g h t s
*There is reason to suspect that the Romans learned of this composition from
the Chinese 3 Mirrorsof the Hellemstlc and Etruscan permds were typically ~10
wt pct Sn alloys But sixteen of eighteen Roman bronze mirrors of the period 100
B C to 300 A D. averaged 21.1 wt pct Sn, the limited range (18 6 to 22.8 pct)
suggests excellent compositional control. Roman trade with the Chinese began in
the first century A D when silk is mentioned for the first trine.
t BlrtnguccLo4 gtves a good description of the process.
:~Bronzemirrors were used for other than frivolouspurposes-one of the most
significant being parabolic mirrors for reflecting astronomicaltelescopes.Newton
made the first practical reflecting telescope m 1672, havingselected a speculum
alloy (6 parts Cu and 2 parts Sn plus As for greater brightness)and ground the
mirror himself. Great astronomical discoveriesduring the next century were made
by James Short, the Herschellsand others by further optical and mechanicalimprovements on reflectingtelescopes wath speculum bronze mirrors.
~Phase diagramsfor each of the major a/toy systems d~scussedin this paper
appear m an Appendtx
w
mirrors were "silvered" in China using tm amalgamas early as second
century B C 6 Whether these techmques were transmitted to the West and applied
to the production of Sn-Hgmirrors on glasssnbstrates has not yet been established.
METALLURGICAL TRANSACTIONS A
,
t
d
,'I.D ! 1~'~ ;n
/
II~,~''' ' /
Fig. 1--A Chinese bronze mirror of the Hart period (206 BC to 220 AD),
done in the shou tai or "ring-of-animals" style, Courtesy of the
F~tzw~ll~am Museum, Cambridge.
+
Fig. 4--The v~olet Cu2Sb or "regulus-of-Venus" formed by immersion
of copper an an acidified annmonal soluhon.
t
Fig. 3--Bronze bull figurine (12.2 x 9.1 cm) found at Horoztepe m
northeastern Anatolia in a chieftan's grave attributed to the Hatt]an
culture of about 2100 BC. Smith's analysis (18) indicates that the
"silvery" coating of Cu3As was applied by a cementation process
involving arsenic vapor. Courtesy of Boston Museum of Fine Arts.
Fig. 41--The presence of "purple plague" (AuAI 2) after thermal aging
of aldminum flying leads which were welded to gold-plated transistor_
leads. Courtesy of L. Zakraysek.
METALLURGICAL TRANSACTIONS A
VOLUME 8A, SEPTEMBER 1977
1329
which w e r e m a i n t a i n e d as a v i r t u a l monopoly by the
g l a s s - m a k e r s of V e n i c e and n e i g h b o r i n g M u r a n o for
over 150 y e a r s . The new p r o c e s s , which r e s u l t e d in
the f o r m a t i o n of an adherent* f i l m of the ? phase or
SnaHg, was d e s c r i b e d in the Encyclopedia of the A r t s
and Science for 1754 as follows:
" T h e foliating of m i r r o r s is p e r f o r m e d thus:
a thin b l o t t i n g - p a p e r is s p r e a d on the table and
s p r i n k l e d with fine chalk, and then a fine leaf of tin
called foil is laid over the paper; upon this m e r c u r y
is poured and d i s t r i b u t e d equally o v e r the leaf. Over
this is laid a c l e a n p a p e r and over that the g l a s s
plate which is p r e s s e d down with the r i g h t hand and
the p a p e r d r a w n gently out with the left. T h i s b e i n g
done, the plate is c o v e r e d with a t h i c k e r p a p e r and
loaden with a g r e a t e r weight so that the s u p e r f l u o u s
m e r c u r y m a y be d r i v e n out and the tin a d h e r e m o r e
c l o s e l y to the g l a s s . When it is d r i e d the weight is
r e m o v e d and the m i r r o r g l a s s is complete. ' ' ~
This p r o c e s s , well i U u s t r a t e d in Fig. 2, t a k e n f r o m
D i d e r o t ' s Encyclopedie, ~~held sway for n e a r l y 400
y e a r s u n t i l t h e m i d - n i n e t e e n t h c e n t u r y when r e p l a c e d
by the c h e m i c a l r e d u c t i o n of s i l v e r n i t r a t e . The h a z a r d s of the t i n - m e r c u r y p r o c e s s have b e e n h u m o r ously, if i n a c c u r a t e l y , m e m o r i a l i z e d i n a bit of v e r s e : ~
Coatings
A very early application of an intermetallic, and
perhaps the earliest, was the cementation of bronze
or copper to produce a coating of Cu3As.lS When
freshly applied, whether by a vapor phase transport
or by dipping in liquid melt, the compoundcould be
highly polished to a beautiful silvery color. Examples of this technique which have been studied include
the Bull of Horoztepe from Anatolia of ~2100 B.C.
(Fig. 3), a copper ewer and basin from Egypt of 2500
to 2200 B.C., and Early Bronze Age axes and halberds
from northern Britain of ~1600 B.C. Apart from these
praiseworthy achievements in the decorative arts,
Biringuccio~9 alludes to fraudulent activities by alchemists and others to counterfeit silver through the
arseniding of copper and similar base metals. Charles2~
and Caley21 have suggested that the intentional manufacture of the first artificial alloy, the ol solid solution
of arsenic in copper, may have been accomplished by
the selection and addition of arsenic minerals; one
such is domeykite, CusAs.
One of the most remarkable of the decorative coatings based on an intermetallic is that derived from the
reaction of copper with antimony to form the beautiful
violet CufSb, knownas the regulus of Venus,m* an il-
L i t t l e Willie, f r o m the m i r r o r ,
Licked the m e r c u r y a l l off,
T h i n k i n g in his childish e r r o r ,
It would c u r e the whooping cough.
At the f u n e r a l , W i l l i e ' s m o t h e r
Sadly said to M r s . Brown,
" T w a s a chilly day for Willie
When the m e r c u r y went d o w n " .
It is of i n t e r e s t to note yet a n o t h e r r o l e played in
the h i s t o r y of technology by i n t e r m e t a l l i c m i r r o r s . In
t h e i r famous e a r l y study of the alloys of steel, F a r a day and Stodart ~2 stated that one of t h e i r t h r e e obj e c t i v e s was to produce i m p r o v e d m e t a l l i c m i r r o r s .
Although m o s t of the alloys p r e p a r e d and studied
were r a t h e r dilute c o m p o s i t i o n s , in t h r e e i n s t a n c e s
i r o n - b a s e d alloys with v e r y l a r g e a m o u n t s of Pt, Pd
or Rh w e r e examined, the l a t t e r e l e m e n t included at
the s u g g e s t i o n of Wollaston. ~s The F e - 5 0 R h alloy was
r e m a r k e d for its u n u s u a l h a r d n e s s , the s p e c u l a r quality of its polished s u r f a c e and its t a r n i s h r e s i s t a n c e .
At this composition, but unknown to F a r a d a y and
Stodart, the C s C l - s t r u c t u r e i n t e r m e t a l l i c , FeRh, can
be produced. When Hadfield ~4 r e e x a m i n e d F a r a d a y ' s
alloys m o r e than 100 y e a r s l a t e r , he was s t r u c k by the
fact that this F e - R h s p e c i m e n was s t i l l e s s e n t i a l l y unt a r n i s h e d . Today, however, we a r e m o r e i n t e r e s t e d
in the u n u s u a l f e r r o m a g n e t i c / a n t i f e r r o m a g n e t i c b e h a v i o r ~5 of this compound than in its a p p l i c a t i o n as a
mirror A
*The mechanism of the adherence process is still not well understood. Tin, of
all the metals, seems to have the greatest affimty for the glass surface. 7 The efficacy of the bonding appears to be improved by workmg with the amalgam s quite
apart from the mechanical and optical properties of the mtermetalhc product
*Interest m the potential of intermetalhc alloys as mirrors has not yet disappeared Testardi et a116 have reported on MosRu and W3Ru2, compounds having
exceptional scratch resistance (1500 to 2000 KHN), good acid corrosion resistance
and high reflectwity (>50 pct that of AI), and the Tin Research Institute 'v recommends electroplated coatings of Cu-45 wt pct Sn (a mLxture of the ~7+ e phases)
for optical reflectors.
METALLURGICAL TRANSACTIONS A
"'"
f
~ .,;~=~.Hi,,.o
. ~,. . . . . .
~
~ , v
~. . . . . . . . . "~..,
.~ . . . , . . . . _
.! . l~..
.
Fig. 2 - " S i l v e r i n g " o f mirrors as practiced in the 18th c e n t u r y . A t (a)
the glass plate is polished as s m o o t h and flawless as possible, p r e f a t o r y
to receiving the m e t a l l i c coating. At (b) a sheet o f tin foil is laid out,
free of wrinkles and creases, and m e r c u r y p o u r e d on and spread over
the surface. After scum and dirt have been removed, sufficient m e r c u r y
is a d d e d to j u s t float the glass plate w h i c h is carefully slid on (c). The
floated plate is then w e i g h t e d w i t h rocks 0') to squeeze o u t excess
mercury. The mirror-to-be is t h e n m o v e d (d) to a t i l t e d rack (g) to
drain f u r t h e r and h a r d e n b y f o r m i n g the SnsHg amalgam b e f o r e being
added to the s h o p ' s i n v e n t o r y (e). The y o u t h f u l appearance o f the
workers in the engraving is likely no mere w h i m of the artist such
were the hazards o f c o n s t a n t h a n d l i n g of m e r c u r y . Plate 255 from
L ' E n c y c l o p e d i e o f Diderot, p. 10, Dover ed., 1 9 5 9 . t
*Needham 23 speculates that this compound may also be identified with the
"purple sheen gold" made by Lou Clung as early as 200 B.C One may also
wonder whether this compound played any role m alchemy where a succession of
color changes white to yellow to purple-was supposed to signal the correct approach to the acluevement of the true Philosopher's Stone. ~
tTlus subject Is the theme of one of the classics of industrial toxicology
[A Kussmanl. Untersuchungen uber den constttutlonellen Mercurialismus und
sere Verhaltnls zur constttutionellen Syphilis, Wurzburg, 1861 ]. Kussrnaul hved
and worked in Furth, Germany, one of the most tmportant nineteenth century
centers for mrrror makmg by the amalgam process
VOLUME 8A, SEPTEMBER 1977
1331
l u s t r a t i o n of w h i c h i s s h o w n i n F i g . 4. It w a s c o m m o n l y p r o d u c e d b y i m m e r s i o n of t h e c o p p e r a r t i c l e in
a n a q u e o u s s o l u t i o n c o n t a i n i n g a n a n t i m o n a l s a l t , e.g.
tartar emetic. Much later this same reaction was
used as a "spot" test for antimony, the so-called
R e i n s c h t e s t . 25.
Dental Restoratives
Another very old alloy, perhaps the oldest intentionally formed ternary alloy based on intermetallics~and surprisingly one still very much in use-is dental
amalgam, a ternary Ag-Sn-Hg alloy which in modern
f o r m u l a t i o n r e s u l t s i n a m i x t u r e of Ag2Hga(7') a n d
Sn~Hg(y2). T h e a l l o y , k n o w n a s yin kao ( s i l v e r f a t o r
ointment) first appears in a T'ang Dynasty materia
m e d i c a (Hsin Hsiu Pen Tshao) w r i t t e n b y Su K u n g in
t h e f o u r t h y e a r of H s i e n C h ' i n g (659 A.D.).26 T h e
author, who is recording what was then a standard
p r a c t i c e , d e s c r i b e s t h e p r o p o r t i o n s of t h e a l l o y , t h e
procedures for its preparation and its special applicability for repairing decayed teeth! Strangely, this
alloy and technique did not become known in the West
u n t i l h u n d r e d s of y e a r s l a t e r . C o p p e r a m a l g a m
(Cu4Hg3) w a s k n o w n a s a d e n t a l r e s t o r a t i v e i n E u r o p e
i n t h e e a r l y 1 5 0 0 ' s , 27 b u t t h e A g - S n - H g c o m p o s i t i o n d i d
n o t a p p e a r u n t i l t h e i n t r o d u c t i o n of " B e l l ' s p u t t y " i n
E n g l a n d i n 1819.$
c o n t e x t . T h e c h o i c e of gold a s a n o b l e m e t a l i s o b v i o u s a n d t h e m e r c u r y , t h o u g h t of a s t h e s e m e n of
R u d r a o r t h e s e e d of S i v a , w o u l d t h u s r e n d e r t h e i c o n
especially efficacious.
W e a r R e s i s t a n t A l l o y s B a s e d o n SbSn
Another very early ternary alloy was type metal
in the Sn-Pb-Sb system, mentioned by Biringuccio as
e a r l y a s 1540.* A l t h o u g h s o m e h a r d e n i n g i s a t t a i n e d
in the Sn-Sb and Pb-Sb simple binary systems, the
b e s t h a r d e n i n g , c o m b i n e d w i t h e a s e of m e l t i n g a n d
good r e n d i t i o n of d e t a i l o n c a s t i n g , i s f o u n d i n t h e
t e r n a r y s y s t e m w i t h t h e f o r m a t i o n of t h e c o m p o u n d
SbSn. Indeed at a later time, an alloy especially prep a r e d f o r t h e p r i n t i n g of s h e e t m u s i c 3~ w a s f o r m e d
f r o m t h e p u r e SbSn p h a s e w h e r e s u p e r i o r h a r d n e s s
was more important than castability. The wear res i s t a n c e of SbSn a l s o c o m m e n d e d i t f o r c o i n a g e p u r p o s e s . A R o m a n R e p u b l i c a n d e n a r i u s of A. P l a u t i u s
w a s f o u n d t o c o n s i s t a l m o s t e n t i r e l y of t h i s i n t e r m e talIic.34 T h e h a r d e n i n g a n t i m o n y i m p a r t s to t i n a n d
t i n - c o n t a i n i n g a l l o y s w a s n o t e d b y G l a u b e r 35 i n 1656,
a n d S m i t h 36 c i t e s i t s u s e a s a h a r d e n e r f o r p e w t e r based pattern material for casting mirror blanks.
Much later Sn-Sb-Cu based alloys, also hardened by
SbSn, w e r e a p p l i e d b y B a b b i t t a s t h e l i n e r m a t e r i a l f o r
s t e e l j o u r n a l b o x e s f o r s t e a m e n g i n e b e a r i n g s in a
f a m o u s 1839 p a t e n t . 37
Miscellaneous Alloys
Ritual Object
P e r h a p s t h e m o s t c u r i o u s of a l l e a r l y a p p l i c a t i o n s
of i n t e r m e t a l l i c c o m p o u n d s i s t h e w o r s h i p of p h a l l i
fashioned from gold amalgam in India and Malaysia.
T h i s p r o c e d u r e i s d e s c r i b e d in t h e Rasaratnasamuccaya a~ a n d i s s u p p o r t e d b y a r e c e n t f i n d of s u c h a n o b j e c t a t t h e C h a n d i B u k i t B a t u P a h a t t e m p l e (12 to 1 3 t h
c e n t u r i e s A . D . ) i n M a l a y s i a . 3~ I t s e e m s q u i t e c e r t a i n
t h a t t h e r e w a s a d e l i b e r a t e a t t e m p t to f o r m t h e h o m o geneous, bulk amalgam rather than merely make a
gilding agent since gold foil was found in the same
*The author is indebted to D. H. Wllklnsfor prepanng the coating on the
coin of Fig. 4, and for pointing out the connection and reference to the Remsch
test.
~-Apossible exception: The Cu-Sn mirrors previously discussedwere sometimes
coated with arsenic which was diffused to form near the surface ternary compomhons containing Cu3Asas well as Cu3Sn. (Cyril Smith: Private commumcatlon.)
~:M.Taveau of Paris is often credited with the first dental application of"sllver
paste" amalgamin 1826, but CharlesBell clearly had precedence 2~For a modern
dlscusmon of the metallurgy of this alloy, see Johnson and Wilsdorf.29
A number of named alloys based on intermetallics
have been selected from Hopkins 33 tabulations and are
summarized in Table I.
The several examples adduced of early alloys based
upon intermetallic compounds, or requiring their presence for development of the desired properties, make
clear that while composition ranges came to be quite
closely controlled and frequently processing conditions
a s w e l l , a l l of t h i s w a s s h e e r e m p i r i c i s m w i t h n o
k n o w l e d g e a n d l i t t l e s p e c u l a t i o n a s to t h e c o n s t i t u t i o n
of t h e a l l o y s y s t e m s i n v o l v e d . O n t h e o t h e r h a n d , i g n o r a n c e of a l l o y c o n s t i t u t i o n d i d n o t p r e v e n t e x p l o r a t o r y e x p e r i m e n t a t i o n a n d s y s t e m a t i z a t i o n of e x p e r i *If Blrlngttcclo's statement (Ref 4, p. 374} is not a mlspnnt, the earliest alloys
were tin-rich with approximately equal, small addmons of lead and antimony. By
the end of the seventeenth century, the preferred composition is quite definitely
m the lead-richcorner, approximatmg the compositions used today. For a discussion, see Smith and Forbes in Singera2and the notes in the Smith and Gnudl
translation of Blrlngucclo 4
Table I. Other Early Intermetallic Based Alloys
Compositmn, Wt Pct
Name
Cu
Zn
Muntz metal
Sorel's alloy
Clark's alloy
Cooper's mirror metal
Cooper's pen metal
Ashberry metal
Birminghamplatinum
Silver bell metal
60 to 62
10
50
58
13.5
38 to 40
80
35
41.5
1332-VOLUME 8A, SEPTEMBER 1977
35
Sn
Ag
Fe
As
Sb
10
27.5
36.5
2.8
65
585
Pt
77.8
50
9.5
50
1.7
194
Base
Compound
Application
3 brass
e brass
Cu3Pt
6 Cu-Sn
(Ag,Cu)PI
SbSn
7 brass
77Cu-Sn
Ship sheathing
Statuary
Imitation gold
Mirrors
Pen nlbs. instruments
Tab/e-ware
Buttons
Table bells
METALLURGICAL TRANSACTIONS A
ence with r e g a r d to the r e l a t i v e s t a b i l i t y of i n t e r m e t a l l i e s , though they were not r e c o g n i z e d as such. F o r
example, the f i r s t attempt to compare and s u m m a r i z e
c o n c i s e l y a l a r g e body of c h e m i c a l o b s e r v a t i o n s on
the r e l a t i v e s t a b i l i t y and i n t e r a c t i o n s of s u b s t a n c e s
was the table of affinities by E t i e n n e - F r a n c o i s Geoffroy ~ (Geoffroy the E l d e r , 1672-1731). Geoffroy, r e p r e s e n t i n g the v a r i o u s s u b s t a n c e s c o n s i d e r e d with
symbols (many of them of a l c h e m i c a l origin*), a r ranged them in columns as shown in Fig. 5, the s e quence in each column being in o r d e r of d e c r e a s i n g
affinity. Thus no substance below a given entry can
r e p l a c e it f r o m a complex formed f r o m the substance
heading the column and that entry; those above, however, can r e p l a c e those below. The tenth column of
Geoffroy's table gives the c o r r e c t sequence of the s t a bility of the a m a l g a m s as shown in Fig. 6. Modern
applications of this p r i n c i p l e a r e found in the P a r k e s
p r o c e s s ~9 for s e p a r a t i o n of gold and s i l v e r f r o m lead
by adding zinc to f o r m A u - Z n and A g - Z n i n t e r m e t a l lics which a r e r e a d i l y s e p a r a t e d by virtue of t h e i r
higher melting point and lower density. Debismuthizing
of lead by a c a l c i u m - m a g n e s i u m addition to form the
compound Bi2(Ca, Mg)3 is yet another example. 4~
SOME MODERN DEVELOPMENTS
The d i v e r s e a r r a y of modern applications of i n t e r m e t a l l i c compounds, ranging f r o m jet engine a l l o y s
(Ni~A1 based)~ to r a z o r blade coatings ( C r 3 P t ) , 43 c o n s t i t u t e an e m b a r r a s s m e n t of r i c h e s to anyone making a
s e l e c t i o n for discussion. Those which will be t r e a t e d
here w e r e chosen b e c a u s e each is totally different
f r o m the o t h e r s and because together they s e r v e well
to i l l u s t r a t e key building blocks to be d i s c u s s e d in the
following section of the p a p e r .
T411LL DI~.S DIFFERENT3 P..4PPO~TS
,'/,,,o ~'~ enOr ,l~l~;',"r
.fub.,l, mcc,,
-e e - e - e
o"
.e , e - e
9
4x
)<
+
9
:3 .
-
o
./% s
2t~, ,r t:l,,J ,r.~ ~ Sloe 9 ,,J
? PC ? \*'\* 6
N
k~/
o
.). Me.*
* 0 ~, ,d,. ,r
7;,,~ ,,A~,.A,,#r 9
(2 g;"~
~ Sof/;~ .,,~e,./
J[~l c.r,. ,
~=4 llpntls
~1 Pit..l.
4; s
0 o,
z~ z,.c
0 S,./
...3, .dnN,~;
PC l ' , o , e C , , / . , , , . . , , . ~ .
~
,,,,w,,,
~(D ~/,',,t~ ~o,o/,,/,,~
~, S,./.,/,-,,/:I;,~
9:t,.,,.
V ~a,,.
~,,~,l~,.,.,~.'q.,t..,~r
Fig. 5 - G e o f f r o y ' s Table of Affinities. The sequence o f a m a l g a m s
s h o w n in the t e n t h c o l u m n f r o m the left (~) is a n a l y z e d in Fig. 6.
*Note that the symbol for copper, ?, also used for Venus, the Goddess of Love
and symbol of beauty, is held by some to represent a pohshed mirror with handle
with which Venus reassured herself that she was fairest of them all.
tThe history of structural apphcalaons of mtermetallic compounds is revmwed
in a previous paper by the author 41 which particularly considers Ni3AI based compositions, and the applications of ordered alloys formed from disordered solid
solutions are considered m another publication.42
METALLURGICAL TRANSACTIONS A
soo
I
400 BINARYAMALGAMS
Maximum
Hg=~
Stability
300
Temperature
o,
/0
/
i/
200
ioo
Sb
Zn
Cu
Pb
Ag
Au
Geoffroy's Stability Sequence
Fig. 6 - M a x i m u m s t a b i l i t y t e m p e r a t u r e s o f b i n a r y a m a l g a m s as t a k e n
from present day phase diagrams c o m p a r e d to G e o f f r o y ' s s t a b i l i t y
sequence.
CosRE Magnets
Beginning about 80 y e a r s ago, the idea slowly developed that a t t r a c t i v e magnetic p r o p e r t i e s could obtain from favorable s t r u c t u r a l d i s p o s i t i o n s of c e r t a i n
atoms, with a f u r t h e r enhancement p o s s i b l e with the
s t r o n g m a g n e t o c r y s t a l l i n e a n i s o t r o p y common in noncubic i n t e r m e t a l l i c s t r u c t u r e s . A well known example
of this concept is the t e r n a r y H e u s l e r a l l o y s (Cu2MnA1
and r e l a t e d compositions).*
Accordingly, it was not s u r p r i s i n g that in the late
1950's two r e s e a r c h groups independently began exp l o r i n g the e x i s t e n c e and magnetic behavior of i n t e r m e t a l l i c compounds f o r m e d between Fe, Co, Mn and
Ni and the r a r e e a r t h e l e m e n t s . At the U n i v e r s i t y of
Pittsburgh, Wallace, a c h e m i s t with a l o n g - t i m e int e r e s t in the synthesis of new compounds of possible
magnetic i n t e r e s t , set his Phi) student, Nassau, to
work on a b r o a d s u r v e y of these b i n a r y s y s t e m s . A
f e w i n s t a n c e s were known of compounds of the MgCu.~
and CaCu5 types between lanthanon elements and Group
VIII t r a n s i t i o n e l e m e n t s of the f i r s t long p e r i o d . Since
these s t r u c t u r e s were based p r i m a r i l y on r u l e s of
r a d i u s r a t i o and e l e c t r o n - t o - a t o m r a t i o and since the
lanthanons were highly s i m i l a r in size and e l e c t r o n i c
s t r u c t u r e , a l a r g e number of i n t e r m e t a l l i c s was expected. Simultaneously, W e r n i c k and a s s o c i a t e s at
Bell Telephone Labs began a s i m i l a r s u r v e y and the
two groups were soon exchanging r e s u l t s . While many
new phases of expected s t r u c t u r e types were found,
no exciting magnetic p r o p e r t i e s were apparent. 46,47
Meanwhile, however, a third g r o u p - Hubbard, Adams
and Gilfrich of the Naval Ordnance L a b o r a t o r y , r e p o r t e d the p e r m a n e n t magnet p r o p e r t i e s of Co~Gd and
c o r r e c t l y identified the i m p o r t a n t r o l e of the l a r g e
m a g n e t o c r y s t a l l i n e a n i s o t r o p y in contributing to the
high c o e r c i v i t y o b s e r v e d . 48
The significance of the l a t t e r work was not i m m e d i *Although this discovery is commonly credited to Heusler,~ he was antimpated
by Hogg. '*s In Hogg's time it was well known that additions of Mn to tron could
produce an alloy in which ferromagnetic behavior was essentially absent; AI addlUons were known to have a similar effect A ternary alloy which Hogg prepared
(73.8 wt pct Mn, 16.2 wt pct Fe, 10.0 wt pct AI) separated on cooling into two
pornons. One exhibited the phenomenon of slow dismtegrahon over a period of
months, the other did not. Both showed marked ferromagnetic behavior. From
Hogg's reported analysis, the dmntegrated alloy can be deduced to have been
primarily the compound MnAl, white the other portion was a Mn-r~ch sohd solution. Elemental manganese is antfferromagnet~c but m certain compounds and
alloys the Mn atoms become sufficmntly separated that the nature of the exchange
is altered from antlferromagnetic to ferromagnenc.
V O L U M E 8A, S E P T E M B E R 1 9 7 7 - 1 3 3 3
120
100
80
CaCu5 STRUCTURE
No. of 60
Examples
4O
2O
0
1930
I
1940
1950
1960
1970
1980
Year
Fig. 7 Chronologicalgrowth in the number of known instances of the
CaCus structure. Points derived from publications by Hauck,s~
Nowotnys~ and Pearson.s2
ately r e c o g n i z e d and it r e m a i n e d for the i s s u a n c e of
an A i r F o r c e r e p o r t in e a r l y 1966 for i n t e r e s t in the
MsRE compounds to be r e i g n i t e d . 49 S t r n a t and H o l l e r
of the A i r F o r c e M a t e r i a l s L a b o r a t o r y had b e e n i n t e r e s t e d for some t i m e in the m a g n e t i c b e h a v i o r of int e r m e t a l l i c s f o r m e d f r o m the i r o n - g r o u p e l e m e n t s
and the r a r e e a r t h e l e m e n t s or y t t r i u m . In o r d e r to
p r o j e c t the p o t e n t i a l of these compounds as p e r m a n e n t
m a g n e t s , they d e t e r m i n e d to m e a s u r e c r y s t a l a n i s o t ropy on single c r y s t a l s a m p l e s . The c r i t e r i a used in
s c r e e n i n g candidate compounds were high s a t u r a t i o n
m a g n e t i s m , a high C u r i e point, and s u f f i c i e n t knowledge of the phase r e l a t i o n s to p e r m i t single c r y s t a l
growth. The finding by S t r n a t and Hoffer of exceptionally high m a g n e t o c r y s t a l l i n e a n i s o t r o p y in Co5Y
p r o m p t e d an i m m e d i a t e and e x t e n s i v e r e e x a m i n a t i o n
of the p e r m a n e n t m a g n e t p r o p e r t i e s of a l l the CosRE
compounds. Once it was known that c o m m e r c i a l l y att r a c t i v e p e r m a n e n t m a g n e t p r o p e r t i e s were a t t a i n able i n the CaCu~ s t r u c t u r e c l a s s , s y s t e m a t i c s e a r c h
for other m e m b e r s of this c l a s s was g r e a t l y i n t e n s i fied with the r e s u l t shown in Fig. 7. B e c k e r r e a l i z e d
that CosSm was much the e a s i e s t to handle of the whole
group and soon produced a 40 k J / m 3 magnet b a s e d on
this compound. 53 The s t o r y of the s u b s e q u e n t s u c c e s s ful c o m m e r c i a l d e v e l o p m e n t of these m a t e r i a l s to
f o r m m a g n e t s with e n e r g y p r o d u c t s in e x c e s s of 160
k J / m 3 has b e e n well told by M a r t i n and Benz s~ and
S t r n a t J s Key f e a t u r e s of this d e v e l o p m e n t were that
it was found n e c e s s a r y to c o n t r o l both s t o i c h i o m e t r y
and p a r t i c l e s i z e d u r i n g the p r o c e s s i n g i n o r d e r to
achieve p r a c t i c a l m a g n e t i c m a t e r i a l s . An i n t e r e s t i n g
l a t e r d e v e l o p m e n t has b e e n the addition of copper to a
CosRE b a s e to produce a p r e c i p i t a t i o n h a r d e n a b l e composition. 56 I n t r i n s i c c o e r c i v e f o r c e s as high 2.4 M A / m
have been a t t a i n e d in such alloys although at s o m e
s a c r i f i c e i n the e n e r g y product p a r a m e t e r . W h e r e a s
in s t o i c h i o m e t r i c CosRE compounds, c o e r c i v i t y is cont r o l l e d by d o m a i n n u c l e a t i o n , i n the copper c o n t a i n i n g
1 : 5 m a t e r i a l s , the d o m i n a n t m e c h a n i s m is d o m a i n
wall p i n n i n g by p r e c i p i t a t e p a r t i c l e s [(Co, Cu)lTRE2]. ~v
The C o s R E - b a s e d c o m p o s i t i o n s a r e not j u s t a n o t h e r
m a g n e t i c m a t e r i a l . T h e i r p r o p e r t i e s r e p r e s e n t new
m i l e s t o n e s of a c h i e v e m e n t , the c o m m e r c i a l exploitation of which has only j u s t begun. The a s s e s s m e n t of
the quality of a p e r m a n e n t magnet is b e s t made by
e x a m i n a t i o n of the d e m a g n e t i z a t i o n c u r v e . The t i m e
t r e n d s i n the d e v e l o p m e n t of two s i g n i f i c a n t p a r a m e 1334 VOLUME8A, SEPTEMBER 1977
t e r s - ( B H ) m a x for e l e c t r i c a l e n e r g y / m a g n e t i c e n e r g y
c o n v e r s i o n a p p l i c a t i o n s and the m a x i m u m r e v e r s i b l e
change in m a g n e t i c f r e e e n e r g y (how the w o r k i n g point
moves along the h y s t e r e s i s curve in the second
quadrant) for " d y n a m i c " a p p l i c a t i o n s such as r e l a y s ,
clutches, or m a g n e t i c s e p a r a t o r s - a r e shown in F i g s ,
8 and 9. V i r t u a l l y a l l the points shown on t h e s e c u r v e s
r e p r e s e n t alloys b a s e d on i n t e r m e t a l l i c s . The upward
t r e n d thus far r e v e a l s no evidence of the p l a t e a u i n g
that m u s t u l t i m a t e l y o c c u r . C o m p a r i s o n of the d e m a g n e t i z a t i o n c u r v e s of two of the CosRE i n t e r m e t a l l i c s
with other p r o m i n e n t p e r m a n e n t m a g n e t s is p r e s e n t e d
in Fig. 10. One of the ways in which these new p r o p e r ties may be exploited is to use the m a t e r i a l to reduce
the size of a p a r t i c u l a r device as, for example, in the
a i r c r a f t engine t a c h o m e t e r shown in Fig. 11. Not only
were the d i m e n s i o n s of the working part of the device
i t s e l f r e d u c e d by the use of the m o r e powerful CosRE
m a t e r i a l , but it was also found that the b e a r i n g s f o r m e r l y r e q u i r e d could now be d i s p e n s e d with, thus
effecting an additional cost r e d u c t i o n .
A- 15 Type Superconductors
The development of commerciallyuseful superconducting intermetallics parallels in many ways the development of the CosRE permanent magnets just re-
kj/m3 1000
500
/ /
/ /
(Sm, Pr)Co s
200
100
50
(BH)max
2O
10
jj//rJ
/t
/
/ f
/
J
6
5
5 / / / / ~
2"
"2
1
1880
,
1900
I
I
I
I
1920 1940 1960 1980
Year
Fig. 8-Chronologtcal improvement m the m a x i m u m energy product
(BH)rnax achieved expenmentally in metallic alloys. 1) carbon steel,
2) W steel, 3) Co steel, 4) Fe-N1-A1alloy, 5) "Tieonal II," 6) "Tlconal
G," 7) "Tlconal GG," 8) "'Ticonal XX." After Zljlstra.s8
1000
kjlm3 500
!
/
SmCos 9 /
200
dF
( S m , Pr) C O s ] , /
100
50
6.7~
20
/ r
///
lO11
1880
I
1900
1920 1940 1960 1980
Year
Fig. 9 -Chronological improvement in the maximum reversible change
of the magnetic free energy, dF, achieved experimentally in metallic
alloys. 1) carbon steel, 2) W steel, 3) Co steel, 4) Fe-Ni-A1,5) "Ticonal
I1," 6) "Tlconal GG," 7) "Ticonal XX." After Zijlstra.58
METALLURGICALTRANSACTIONSA
B-H Curves (1973)
1.0
.8
.6 Induction
.4 Tesla
1000' 900 '80~ '7()0 '600 '500 '4(}0 '300' 200 100
.2
0
-.2
-H kA/m
%4
Fig. l 0-Second quadrant B-H curves of leading permanent magnet
materials.
of both the p r o c e s s i n g d e v e l o p m e n t and the high c r i t i cal c u r r e n t c h a r a c t e r i s t i c was that high field s o l e n o i d s
then s e e m e d f e a s i b l e . Within two y e a r s of the r e p o r t
of K u n z l e r et al, B e l l Labs had built a 7 t e s l a s o l e noid. The s t r e n g t h of such s o l e n o i d s has s i n c e b e e n
s t e a d i l y pushed up with i m p r o v e m e n t s in p r o c e s s cont r o l and d e s i g n i n n o v a t i o n s . The l a t e s t r e c o r d c r y o genic m a g n e t (see F i g . 14) is one of 17.5 t e s l a ( m o r e
than 350,000 t i m e s the s t r e n g t h of the e a r t h ' s m a g netic field! )* built by I n t e r m a g n e t i c s G e n e r a l C o r p o r ation for the J a p a n e s e N a t i o n a l R e s e a r c h I n s t i t u t e f o r
M e t a l s .66 T h i s new m a g n e t is c o m p r i s e d of two conc e n t r i c i n t e r m e t a l l i c windings; the o u t e r one, of Nb3Sn
tape, p r o d u c e s 13.5 t e s l a while the i n n e r , f o r m e d f r o m
the i s o m o r p h o u s V3Ga p r o d u c e s 4.0 t e s l a . The c h o i c e
of V3Ga for the i n n e r winding is b a s e d on the fact that
its c r i t i c a l c u r r e n t v a l u e is about 10 t i m e s that f o r
Nb3Sn.
The p r o c e s s i n g innovations which b r o u g h t s u p e r -
100
8O
m
No. of
Examples
A-15 STRUCTURE
W
~
era Si o r / 3
60
40
2o
Fig, 11-Aircraft engine tachometer; left and center, conventional constructxon with bearings, right, with substitution of CosRE magnets.
Courtesy of P. Frischman, General Electric Company.
v i e w e d . The f i r s t s u p e r c o n d u c t i n g compound, Au2Bi,
was found by d e H a a s et al in 1929.59 Hardy and Hulm, 6~
then (1953) at the I n s t i t u t e f o r the Study of M e t a l s at
the U n i v e r s i t y of Chicago, undertook a s u r v e y of s i l i c i d e s and g e r m a n i d e s for t h e i r p o s s i b l e s u p e r c o n d u c t ing b e h a v i o r b e c a u s e of s o m e s u s p e c t e d s t r u c t u r a l
a n a l o g i e s to c a r b i d e s , n i t r i d e s and b o r i d e s , many of
which w e r e known to be s u p e r c o n d u c t i n g . S e v e r a l
s u p e r c o n d u c t i n g compounds w e r e d i s c o v e r e d with the
fi-W, o r m o r e p r o p e r l y Cr3Si s t r u c t u r e , and one of
these, V3Si, exhibited a then (1953) new r e c o r d s u p e r conducting t r a n s i t i o n t e m p e r a t u r e , 17.8 K. T h i s s t r i k ing r e s u l t s t i m u l a t e d a b r o a d s e a r c h f o r o t h e r [3-W
s t r u c t u r e compounds by a group at B e l l Labs led by
M a t t h i a s . T h e s e w o r k e r s , guided by the s a m e concepts
of r e l a t i v e a t o m s i z e and e~a r a t i o that had b e e n found
o p e r a t i v e for other i n t e r m e t a l I i c compounds, d i s c o v e r e d many m o r e s u p e r c o n d u c t i n g A - 1 5 compounds,
one of which Nb3Sn had a s u p e r c o n d u c t i n g t r a n s i t i o n
t e m p e r a t u r e , Tc, of 18.05 K. 61 T h i s d i s c o v e r y t r i g g e r e d a s e a r c h , s t i l l on-going, for m o r e A - 1 5 i s o m o r p h s with the r e s u l t shown in F i g . 12. The c r i t i cality of the e / a r a t i o to T c is w e l l shown in F i g . 13.
The i m p e d i m e n t to p r a c t i c a l e x p l o i t a t i o n of the unusually high T c lay, as so f r e q u e n t l y is the c a s e with
i n t e r m e t a l l i c s , in the v e r y b r i t t l e b e h a v i o r of the c o m pound. H o w e v e r , when c l e v e r p r o c e s s i n g d e v e l o p m e n t s
by a n o t h e r B e l l Labs group 65 p e r m i t t e d the p r o d u c t i o n
of Nb3Sn in f i l a m e n t a r y f o r m , a new and m o r e i m p o r tant c h a r a c t e r i s t i c was a p p a r e n t : high c r i t i c a l c u r r e n t s
(>101~ A / m 2 in f i e l d s of 8.8 t e s l a ) . T h e s i g n i f i c a n c e
METALLURGICALTRANSACTIONSA
.,~',
L.b3sn,rc = 18~os~
~ . 4 ' P L 1StSuperconducting
example
0
~
'
1930
i
1940
1950
1960
Year
1970
1980
Fig. 12-Chronological growth in the number of known instances of
the A 15 structure. Points derived from publications by Boren,6z
Pearson, s2 Hartsough. 6a
20
4.7
9 Superconductive
transitiontemperature
T Notsuperconductive
tothistemperature
15
6.5
Tc (~
i
10
L'
I
I
I
!
5
~" "~.I" ,
o
.~
"l
9 .I
"1
t 9'I,
!
I' .-I
!
I
I
,
I
o I
9
I
i
1 2 3 4
5 6 7 8
Valence Electrons/Atom
Fig 13-Dependence of superconducting critical temperature on
average number of valance electrons per atom for A 15 (Cr20) type
compounds. After Roberts. 64
*A more meaningfulcomparlsup lS to point out that a conventionalsolenoid
would require severalmegawattsof power to produce a comparable field, whalem
a superconductmgmagnet, once excitedand shorted, currents wtllorculate foreverv]rtuallywithout loss.
VOLUME 8A, SEPTEMBER 1977-1335
c o n d u c t i n g i n t e r m e t a l l i c s to c o m m e r c i a l p r a c t i c a l i t y
w e r e p r i m a r i l y t h r e e . F i r s t to f o r m t h e c o m p o u n d b y
a diffusion process so as to keep it dimensionally
small and therefore more amenable to mechanical
h a n d l i n g , s e c o n d l y to d i s p e r s e t h e s u p e r c o n d u c t i n g
e l e m e n t s i n t h e s t r u c t u r e s o t h a t l o c a l t r a n s i t i o n s to
"normal"
c o n d u c t i o n do n o t p r o p a g a t e t h r o u g h o u t
t h e w h o l e s t r u c t u r e ( s e e F i g . 15) a n d f i n a l l y to c o n t r o l
t h e c o m p o s i t i o n c l o s e to t h e s t o i c h i o m e t r i c r a t i o . * T h e
m u c h g r e a t e r i n f l u e n c e of s t o i c h i o m e t r y t h a n of l o n g
r a n g e o r d e r i s s h o w n i n F i g , 16. T h e c r i t i c a l i t y of
s t o i c h i o m e t r i c c o n t r o l u n d e r l i n e s t h e i m p o r t a n c e of
t h e k n o w l e d g e of p h a s e d i a g r a m s t o s u p e r c o n d u c t o r
development.~
"Tribaloy"
Bearing Materials
A s we h a v e s e e n , t h e a p p l i c a b i l i t y of i n t e r m e t a l l i c s
to the bearing field was recognized (stumbled upon?)
q u i t e e a r l y ( B a b b i t t ' s a l l o y s w i t h SbSn).$ H o w e v e r , a s
*
*'
*
'"
o
.-
. . . . .
bearing technology moved from art toward science,
some metallurgical criteria for optimum performance
b e g a n to e m e r g e . F o r l o a d s u p p o r t a n d w e a r r e s i s t ance a hard phase is required; this hard phase must be
compatible with a softer, tenacious matrix in which it
is carried; the hard phase should be stable and inert
with respect to the journal material and any oxide
films formed at service temperatures should be selfprotective and nongalling. These criteria are admirably met by intermetallic compounds, particularly
when an alloy composition is selected which results in
a h i g h p r o p o r t i o n of t h e i n t e r m e t a l l i c p h a s e i n e q u i l i brium with a soft, tough solid solution or eutectic
m a t r i x . T h e w o r k of B u c k l e y a n d J o h n s o n 73 e m p h a s i z e d t h e r o l e of c r y s t a l s t r u c t u r e i n f r i c t i o n a n d w e a r
and indicated that improved performance should be att a i n e d w i t h c o m p o u n d s of h e x a g o n a l s t r u c t u r e a n d h i g h
-
~,.u~-~,.-::::
..... -,
~,~;~...::::::---..---
Fig. 15-Mmrograph of the filamentary structure oI Nb3Sn in a bronze
matrix. Courtesy of C. H. Rosner, Intermagnetics General Corporatxon.
f
|
I
m
i
i
i
]1 L
20
..,all
mc
oNb--Ge
(*K)
Nb--AI
/ / /
//
_
15
10
"
f
Fig. 14-Superconducting solenoid 17.5 tesla electromagnet with concentric windings of VsGa (inner) and Nb3Sn (outer). Bore is 3.1 cm.
Courtesy of C. H. Rosner, Intermagnetlcs General Corp.
*It is cunous that recent further processingdevelopments67involve the reactaon ofmobmm wires with bronze one of the oldest known alloys to form this
Nb3Sn superconductor of the present "space age."
tUseful recent revmwsof this subject, other than those already cited, include
Dew-Hughes,69Sav]tskn,7~Hem71and Geballeand Hulm.72
:~Other bearing alloys have as the critical constituent such mtermetalhcs as
Pb3Ca, CuSn, Na2Pbs, CuCd3, CusCdsand NICdT.
1336-VOLUME 8A, SEPTEMBER 1977
t
s
DV--Ga
9 V--Si
a
I
I
I
I
I
I
0.20
,8
,
0.25
Fig. 16-Comparison of the effects of order and stoichiometric deviation on the super-conducting transition temperature in mobium and
vanadium based A 15 compounds. Variations in the state of order induced by heat treatment did not affect Tc by more than 10 pct. Alternatively variations in the compositional parameter/3 (formulating
the compounds as A T 13B~3)of as little as 4 pct changed T c by 8 K.
After Fltiklger. 6a
METALLURGICAL TRANSACTIONS A
c / a ratio, exhibiting p r i m a r y b a s a l slip. Two f u r t h e r
g e n e r a l i z a t i o n s came f r o m this s a m e l a b o r a t o r y : o r d e r e d s t r u c t u r e s gave lower coefficients of f r i c t i o n
than d i s o r d e r e d s t r u c t u r e s of the s a m e composition; TM
and additions of s i l i c o n , even to o r d e r e d p h a s e s , f u r ther lowered the f r i c t i o n a l coefficient. 7~
Schmidt and F e r r i s s of DuPont, TM in s e a r c h i n g for
new alloy c o m p o s i t i o n s which would exhibit low f r i c tion and high c o r r o s i o n and wear r e s i s t a n c e in nonl u b r i c a t i n g e n v i r o n m e n t s , built upon the i n s i g h t s of
this e a r l i e r work. They s c r e e n e d h u n d r e d s of m e t a l
p a i r s in a p i n / d i s c r o t a r y t h r u s t t e s t e r paying p a r t i c u l a r a t t e n t i o n to s i l i c o n - c o n t a i n i n g alloys in which
i n t e r m e t a l l i c s having the d e s i r e d c / a r a t i o might be
f o r m e d . O u t s t a n d i n g b e h a v i o r was o b s e r v e d with alloys c o n t a i n i n g a t e r n a r y i n t e r m e t a l l i c compound in
the C o - M o - S i s y s t e m . T h i s compound, which m a y be
w r i t t e n Mo(Co, Si)z, extends o v e r the r a n g e 15 to 30 at.
pct Si and is a L a v e s s t r u c t u r e of the MgZn~ type. It
was f i r s t d i s c o v e r e d by G l a d y e s h e v s k i i and K u z ' m a 7r
and the t e r n a r y d i a g r a m worked out by Skolozdra el
al.TS
Once the unique t r i b o l o g i e a l b e h a v i o r of the eompound was a p p r e c i a t e d , the DuPont s c i e n t i s t s p r o ceeded to develop a s e r i e s of C r - c o n t a i n i n g c o m p o s i tions b a s e d on Mo(Co, Si)~ or its i s o m o r p h Mo(Ni, Si)e,
where the b a l a n c e of wear r e s i s t a n c e , c o r r o s i o n r e s i s t a n c e and e a s y f a b r i c a t i o n is d i f f e r e n t l y a r r a n g e d
depending on the p a r t i c u l a r application and the intended
mode of f a b r i c a t i o n . P r e s e n t l y , four d i s t i n c t alloys,
sold u n d e r the t r a d e n a m e " T r i b a l o y " , have b e e n developed and a r e applied (either as such or b l e n d e d v i a
powder m e t a l l u r g y t e c h n i q u e s with other m a t e r i a l s ) in
such d i v e r s e a r e a s as valve facings for m e t h a n e fueled e n g i n e s , wear i n s e r t s for c o m p u t e r tape heads,
m e c h a n i c a l face s e a l s , gear pumps, and s l e e v e b e a r ings for s n o w m o b i l e torque c o n v e r t e r s . In these s e r vice a p p l i c a t i o n s , as well as in the f o r e - m e n t i o n e d
l a b o r a t o r y w e a r / c o r r o s i o n t e s t s , the T r i b a l o y comp o s i t i o n s s u b s t a n t i a l l y o u t p e r f o r m e d such t r a d i t i o n a l
m a t e r i a l s as Cobalt Alloy 6, Hastelloy C, WC-Co, CoC r - W - C hard facing, and 80-10-10 leaded b e a r i n g
b r o n z e . C o n s i s t e n t with the s t a t e m e n t above, T r i b a l o y
Fig. 17-Microstructure of cast Tribaloy T400 showing primary
Mo(Co,Si)~ and eutectic between the compound phase and the sorer
solid solution, Marble's etch, oblique illumination (magmficatmn
570 times)9ARer Schmidt and Ferris. ~6
METALLURGICALTRANSACTIONSA
, ,, i ~ .
Ib
Fig. 18-Surface of a Tribaloy sample after rotary thrust wear test.
Test ring A1SI 4620, 60 Rc, load 2669 N, velocity 7.9 m/min, time 1
h, (magmfication 57.4 times). Note neither galhng or scratching
are visiblein wear track; rather ~t shows an almost "metallographic" pohsh.
c o m p o s i t i o n s have proved to f o r m an a d h e r e n t s e l f l u b r i c a t i n g oxide at 500~ or above. The soft oxide,
CoMoO4, f o r m s in air r a t h e r than an a b r a s i v e oxide
such as Cr203. This novel f e a t u r e m a k e s these alloys e s p e c i a l l y useful in w e a r i n g a p p l i c a t i o n s at m o d e r a t e a m b i e n t t e m p e r a t u r e s or where c o m p a r a b l e i n t e r f a c i a l
t e m p e r a t u r e s develop d u r i n g o p e r a t i o n , A t y p i c a l m i e r o s t r u c t u r e of T r i b a l o y 400 is shown in Fig. 17 and
the r e s u l t s of a wear t e s t in Fig. 18.
THE
ORIGIN
OF
SOME
KEY
CONCEPTS*
P r i o r to the m i d - n i n e t e e n t h c e n t u r y , d e v e l o p m e n t s
in the m e t a l l u r g i c a l field ( i n t e r m e t a l l i c or otherwise)
came slowly indeed. P r a c t i c a l l y useful d i s c o v e r i e s
w e r e not made by s c i e n t i f i c r e s e a r c h but r e s u l t e d
f r o m the o b s e r v a t i o n s of an u n u s u a l l y a t t e n t i v e a r t i s a n e i t h e r in the c o u r s e of his r e g u l a r work or f r o m
an u n w e a r y i n g s e a r c h of a l l a v a i l a b l e m a t e r i a l s and
t e c h n i q u e s . Once noted, f u r t h e r i m p r o v e m e n t on the
u s e f u l r e s u l t was sought f r o m the a p p l i c a t i o n of s i m i l a r
m a t e r i a l s and t e c h n i q u e s . But r e c o g n i t i o n of the e s s e n t i a l e l e m e n t in the d i s c o v e r y was difficult at b e s t
and even d u p l i c a t i o n of the r e s u l t u s u a l l y r e q u i r e d an
e x t r a o r d i n a r y d e g r e e of m a n i p u l a t i v e skill, given
the c r u d i t y of e x i s t i n g e q u i p m e n t . Hence, it is little
wonder that p r a c t i c a l d i s c o v e r i e s once made p e r s i s t e d
for h u n d r e d s of y e a r s b e f o r e d i s p l a c e m e n t by a l a t e r
improvement. Further, lacking a fundamental under*"It Is an extremelyusefulthingto have knowledgeof the tree originsof
memorablediscoveries,especiallythose that havebeenfoundnot by accidentbut
by dintof meditation,It is not so muchthat therebytustorymay attributeto
each man his ow~ discoveriesand othersshouldbe encouragedto earn likecommendation,as that the art of makingdiscoveriesshouldbe extendedby considering noteworthyexamplesof it " Llebmz Historiaet OrigoCalculiDifferentalis,
1676.
VOLUME 8A, SEPTEMBER 1977-1337
s t a n d i n g of the u n d e r l y i n g p h y s i c a l m e t a l l u r g y , it was
v i r t u a l l y i m p o s s i b l e f o r t h e s e e a r l y w o r k e r s to gene r a l i z e f r o m t h e i r o b s e r v a t i o n s and extend t h e i r findings to o t h e r al l o y s y s t e m s . In c o n t r a s t , in the m o d e r n
p e r i o d , although chance p l a y e d s o m e r o l e in e a r l y obs e r v a t i o n s , u n d e r s t a n d i n g had so i m p r o v e d and c o m pi l at i o n s of b a s i c data had a m a s s e d to the point that
r e l a t i v e l y r a p i d e x p l o i t a t i o n was now f e a s i b l e . On the
o t h e r hand, as we h a v e s e e n , m a t e r i a l s n e e d s c a l l e d
out by d e v e l o p m e n t s in f u n d a m e n t a l s c i e n c e (e.g. su p e r c o n d u c t i v i t y ) have s t i m u l a t e d s e a r c h e s f o r new
compounds that w e r e guided by " e n l i g h t e n e d e m p i r i c i s m " ; and t h e s e s e a r c h e s in turn have added
t r e m e n d o u s l y to our s t o r e of b a s i c i n f o r m a t i o n on
intermetallics.
What w e r e the key c o n c e p t s that p e r m i t t e d the m o d e r n i n t e r m e t a l l i c d e v e l o p m e n t s j u s t r e v i e w e d ? To
a n s w e r this question, a c e r t a i n a r b i t r a r i n e s s is una v o i d a b l e . F o r the p u r p o s e s of this r e p o r t , the choice
has b e e n b a s e d on f a c t o r s m o r e or l e s s c o m m o n to al l
t h e s e e x a m p l e s d i s c u s s e d and on m e t a l l u r g i c a l a s p e c t s r a t h e r than t h o s e d e r i v i n g f r o m p h y s i c s o r s c i ence g e n e r a l l y .
The f a c t o r s s e l e c t e d f o r f u r t h e r e x a m i n a t i o n of t h e i r
historic roots are:
9 the d e v e l o p m e n t of the m o d e r n c o n c e p t of the int e r m e t a l l i c compound
* the d e v e l o p m e n t of the phase d i a g r a m
= the r o l e of e l e c t r o n c o n c e n t r a t i o n in d e t e r m i n i n g
intermetallic phase stability
= the r o l e of g e o m e t r i c a l f a c t o r s in d e t e r m i n i n g int e r m e t a l l i c phase stability
9 the point d e f e c t c o n c e p t and its r e l a t i o n to nons t o i c h i o m e t r i c compounds
9 the u n u s u al r o l e of g r a i n b o u n d a r i e s in i n t e r m e t a l l i c compounds.
The i n t e r r e l a t i o n s h i p s b e t w e e n t h e s e key building
b l o c k s a r e shown in F i g . 19. It can be s e e n that t h e r e
a r e a n u m b e r of f u n d a m e n t a l c h e m i c a l c o n c e p t s that
w e r e e s s e n t i a l ; t h e s e in t u r n s u p p o r t c e r t a i n m e t a l l u r g i c a l ideas; f r o m the l a t t e r d e r i v e the p r i n c i p l e s
j u s t cited of s p e c i a l p e r t i n e n c e to i n t e r m e t a l l i c s , and
t h e s e fi n al l y c o n t r i b u t e to the a c h i e v e d a p p l i c a t i o n s .
with s a l t s o l u t i o n s , and by R i c h t e r (1794) who e x a m i n e d
a c i d - b a s e n e u t r a l i z a t i o n and so extended the notion of
e q u i v a l e n t w e i g h t s . The t r u e beginnings of q u a nt i t a t i v e c h e m i s t r y m ay p r o p e r l y be a s s o c i a t e d with L a v o i s i e r who in 1789 e n u m e r a t e d t h i r t y - o n e d i s t i n c t e l e m e n t s . In that s a m e y e a r Higgins s u g g e s t e d that the
c o m b i n a t i o n of d i f f e r e n t e l e m e n t s to f o r m a compound
might be p o s s i b l e only with c e r t a i n weight p r o p o r tions of each. A full t h e o r y of the c o m b i n i n g b e h a v i o r
of the e l e m e n t s was propounded by Dalton, i n i t i a l l y in
an 1803 p a p e r and l a t e r in his 1808 m o n o g r a p h , " A
New S y s t e m of C h e m i c a l P h i l o s o p h y " . Th e e x p e r i m e n t a l r e s u l t s of P r o u s t and B e r z e l i u s , as w e l l as of
Dalton, t o g e t h e r with the t h e o r e t i c a l t r e a t m e n t s by
A v o g a d r o and C a n n i z a r o , put the D al t o n t an t h e o r y of
c h e m i c a l f o r m u l a t i o n and his Law of M u l t i p l e P r o p o r t i o n on f i r m ground d e s p i t e the c h a l l e n g e of B e r t h o l l e t that the weight p r o p o r t i o n s of e l e m e n t s in a
compound w e r e not i m m u t a b l e but r e s u l t e d f r o m the
r e a c t a n t p r o p e r t i e s , p r o p o r t i o n s and conditions of r e act i o n . A v o g a d r o a t t e m p t e d to r e c o n c i l e the opposing
v i e w p o i n t s of P r o u s t and Dalton on the one hand and
B e r t h o l l e t on the o t h e r , w r i t i n g : 82
"If we c o n s i d e r the a p p r o a c h of m o l e c u l e s in solid
o r liquid b o d i e s , when the s p a c e s b e t w e e n the i n t e g r a t i n g m o l e c u l e s a r e not of the s a m e o r d e r as t hos e
b e t w e e n the e l e m e n t a r y m o l e c u l e s , c o m b i n a t i o n s
m ay o c c u r in c o m p l i c a t e d p r o p o r t i o n s , but t h e s e
c o m b i n a t i o n s a r e of a d i f f e r e n t n at u r e; this i d e a
m a y s e r v e to r e c o n c i l e the i d e a s of B e r t h o l l e t with
the t h e o r y of f i x ed p r o p o r t i o n s . "
We s e e h e r e f o r e s h a d o w e d the concepts l a t e r to be
shown to be so r e l e v a n t to i n t e r m e t a l l i c c o m p o u n d s that i n t e r a t o m i c s p a c i n g depends on the identity of the
c o m b i n i n g p a i r and that s i z e d i f f e r e n c e s b e t w e e n
s p e c i e s m ay f a v o r c e r t a i n a t o m i c p r o p o r t i o n r a t i o s .
R u d i m e n t a r y as was the knowledge of c h e m i c a l c o m pounds g e n e r a l l y in the e a r l y n i n e t e e n t h c e n t u r y , it
was s u p e r i o r to the situation with r e s p e c t to i n t e r m e t a l l i c s , for t h e r e was n o s c i e n c e of a~loys. P l e a s
Th e I n t e r m e t a l l i c Compound Concept
It is d i f f i cu l t now to a p p r e c i a t e the s t r u g g l e it was
even as late as the e i g h t e e n t h c e n t u r y to s e t up a
p r o p e r c l a s s i f i c a t i o n of s u b s t a n c e s and to d i s t i n g u i s h
b e t w e e n t r u e e l e m e n t s and c o m m o n compounds.* Most
s u b s t a n c e s w e r e c h a r a c t e r i z e d by t h e i r p h y s i c a l at t r i b u t e s , f o r c h e m i c a l m e a n s of d e t e r m i n i n g t h e i r cons t i t u e n c y w e r e lacking. T h e t r u e n a t u r e of a c o m pound could be r e a l i z e d only when it could be a n a l y z e d
and s y n t h e s i z e d ; in the a b s e n c e of such t e c h n i q u e s the
identity of s a m p l e s of the s a m e compound p r e p a r e d
by d i f f e r e n t r o u t e s could not e v e n be e s t a b l i s h e d . Key
a d v a n c e s in the r o a d t o w a r d m o d e r n c o n c e p t s of c o m pound f o r m a t i o n w e r e m a d e by W e n z e l (1777) in what
we would now c a l l double d e c o m p o s i t i o n e x p e r i m e n t s
*Thetustory of compoundchemistry is very rich and it is not possible to treat
it here m any detad. Workswhichthe author has found especiallyuseful on this
topic mcludethe books by Partington,79Berry8~and Freund?1Theseworks mclude the full referencesto the seminalpublicationscited m thls paragraph
1338-VOLUME 8A, SEPTEMBER 1977
~
APPL,cATIo.sJ/
Nb3Sn superconductor f /
CosSm magnet
J
J
Mo (Co,SI)2 bearing
Fig. 19-Chart showmg the lineage of key concepts of intermetallic
format]on and behav]or (rectangles) from metallurgical concepts
(triangles) and ultimately from fundamental concepts of chemistry and
physics (ellipses).
METALLURGICAL TRANSACTIONS A
f o r s y s t e m a t i c study of a l l o y s had begun with Bacon*
(1627), but l i t t l e was done along this line f o r m a n y
y e a r s ~ e x c e p t i n g the o u t s ta n d in g book p u b li s h e d by
A c h a r d 8s in 1788 which was not followed up by o t h e r
w o r k e r s . A c h a r d c o r r e l a t e d the many p r o p e r t i e s he
m e a s u r e d with c o m p o s i t i o n in a l m o s t 900 a l l o y s , both
b i n a r y a l l o y s of e l e v e n d i f f e r e n t m e t a l s and m o r e c o m plex a l l o y s containing up to s e v e n c o m p o n e n t s ! U n f o r t u n a t e l y , he paid no a tt e n ti o n to t h e i r p o s s i b l e cons t i t u t i o n mad, indeed, p r e s e n t s only b a r e - b o n e s r e s u l t s
in t a b u l a r f o r m without d i s c u s s i o n o r s p e c u l a t i v e int e r p r e t a t i o n . $ T h u s , in 1803 H a t c h e t t 87 was s t i l l r e c o m m e n d i n g that
" a n i m m e n s e addition to m e t a l l u r g i c a l s c i e n c e
would, in a l l p r o b a b i l i t y , be d e r i v e d f r o m a c o m p a r a t i v e i n v e s t i g a t i o n of the whole of the known m e t a l l i c s u b s t a n c e s , f o r m e d into b i n a r y , t e r n a r y , and
such like c o m b i n a t i o n s , p r o c e e d i n g f r o m the m o s t
s i m p l e to the m o s t c o m p l i c a t e d , and a c c o m p a n i e d
by a c c u r a t e o b s e r v a t i o n s on the l u s t r e , c o l o u r ,
d u c t i l i t y , h a r d n e s s , s p e c i f i c g r a v i t y , and f u s i b i l i t y
of the c o m p o u n d s . 8 2
D u r i n g the f i r s t half of the n i n e t e e n t h c e n t u r y , it is
c l e a r both f r o m H a t c h e t t and o t h e r c o n t e m p o r a r y
w r i t e r s that the c o n c e n s u s of thought was that m o s t
a l l o y s w e r e s p e c i f i c c h e m i c a l c o m b i n a t i o n s with
unique p r o p e r t i e s , not p r e d i c t a b l e f r o m t h o s e of the
c o n s t i t u e n t m e t a l s . T h i s s a m e v i e w was e x p r e s s e d
by F a r a d a y in his 1837 l e c t u r e s and r e p o r t e d by
H e n r y . w By this t i m e s e v e r a l s o l i d compounds had
b e e n i s o l a t e d f r o m a m a l g a m s (KHg, Hg2NaK), 9~ f r o m
Cu- S n m e l t s (CuSn), 92,9~ and by a c i d s e p a r a t i o n f r o m
s l o w l y c o o l e d a l l o y s (CuZn). ~4
E v i d e n c e of the p e r s i s t e n c e of r i g i d a d h e r e n c e
to a t o m i c p r o p o r t i o n a t i o n is a f f o r d e d by S i l l i m a n 95
(1847) who propounds that " A l l o y s a r e c h e m i c a l
c o m b i n a t i o n s and a r e u s u a l l y b e s t s u i t e d to a r t i f i c i a l
p u r p o s e s when m a d e in the a t o m i c p r o p o r t i o n s of
the s e v e r a l m e t a l s " ; and C a l v e r t and J o h n s o n 9e
(1855) s t a t e " W e . . . b e l i e v e , that by p r o d u c i n g a l l o y s
*"Withwhat metalsgoldwillIncorporate by simplecoliquefaction,and with
what not? And in what quantity willit incorporate;and what kind of body the
compound makes?" Ref. 83.
tone instance whichshould be cited Is the work of Geoffroy~ who prepared
and studied a seriesof alloysin the Cu-Znsystem. By observationof their physical
properties and especiallyof their fracture behavior,he distinguishedbetween
alpha, beta, and gammabrass
~CyrilSmith86has appraisedthis paper vath admirationm a fascinatingand
scholarly analysis
82 motwatlon for this paper was a requestby the PrivyCouncilon behalfof
the Roya]Mint that an investigationbe made of the effectsof aJloymgon the wear
of goldcorns. To this end Hatchett (with the assistance of Cavenchsh)made up
numerous binary goldalloysand devisedan elaborate machine which they hoped
wouldsimulatethe natural wearof corns tumbhng againstone another in a person's pocket. Hatchetthad a longhfe (1765-1847) but his Important scientific
work was accomplishedm a singledecade 1796-1806. Among his notable contributions are the discoveryof columbium(Hatchett's name) and the training of W.
T. Brande who eventuallysucceededDavyat the RoyalInstitutmn. For a description of Hatchett's work, see Weeks.as
w (Faraday) then spoke of the alloysand the amalgamsof metals and
stated the fact that they are all definitecompounds. Whenthe metals are mixed
m any other proportion than those proper to form the relativeatomic weights, a
definite compound takes place a~aongthe parts of the materialsand the remainder
formwscous real mixtureswinchin somecasesmay be separated by snnple means"
(from Joseph Henry'sEuropean charyof April 1837 excerptedby Remgold).89
METALLURGICALTRANSACTIONS A
h a v i n g a definite c o m p o s i t i o n ( i . e . i n t e r m e t a l l i c s ) ,
we
should point the way to much c h e a p e r and b e t t e r a l l o y s
than h i t h e r t o . . . " R u d b e r g ' s 97 (1830) and l a t e r
L e v o l ' s 98 (1850) finding of constant m e l t i n g point a l loys at c e r t a i n low m e l t i n g c o m p o s i t i o n s led t h e m to
c l a i m t h e s e to be compounds, e . g . PbSn3 and Ag3Cu2,
w h e r e a s we now know t h e m a s e u t e c t i c s having no n e c e s s a r y r e g u l a r i t y in t h e i r p r o p o r t i o n s . Although
G u t h r i e 99 (1884) e s t a b l i s h e d the t r u e c h a r a c t e r of s u c h
a l l o y s , e v e n the g r e a t O s m o n d 1~176
in 1904 was s t i l l
confused as to w h e t h e r or not e u t e c t i c s w e r e i n t e r m e t a l l i c c o m p o u n d s . As late as 1896 B r a n n t TM was s t i l l
a r g u i n g the a d v a n t a g e s of a l l o y s f o r m u l a t e d in a t o m i c
proportions.
" I t is known that the e l e m e n t s a l w a y s c o m b i n e with
one a n o t h e r in c e r t a i n q u a n t i t i e s by weight which a r e
t e r m e d a t o m i c w ei g h t s . . . By m i x i n g the m e t a l s
a c c o r d i n g to e q u i v a l e n t q u a n t i t i e s , a l l o y s of d e t e r m i n e d c h a r a c t e r i s t i c s a r e , as a r u l e , obtained. If
t h e s e p r o p e r t i e s do not a n s w e r the d e m a n d s made
of the alloy, the o b j e c t is f r e q u e n t l y a t t a i n e d by t a k ing two, t h r e e o r m o r e e q u i v a l e n t s of one m e t a l . An
e x c e p t i o n to this r u l e is only made in c e r t a i n
cases..."
A b a s i c i m p e d i m e n t was that e x p e r i m e n t a l v e r i f i c a tion of t h e s e f u n d a m e n t a l c o n c e p t s of compound f o r m a t i o n and c r y s t a l c h e m i s t r y was l i m i t e d to d e t e r m i n i n g the r e l a t i v e w e i g h t s of a t o m s and the p r o p o r tions of e l e m e n t a l s p e c i e s p r e s e n t . T h e r e w e r e
s e v e r a l d i f f i c u l t i e s . F i r s t , i s o l a t i o n of compounds
f r o m s o l i d o r liquid a l l o y s by m e c h a n i c a l m e a n s , by
d i s t i l l a t i o n of the e x c e s s of a v o l a t i l e e l e m e n t o r by
t r e a t m e n t with a c i d s , liquid a m m o n i a o r m e r c u r y was
u s u a l l y quite i m p e r f e c t , thus l e a d i n g to many s p u r i o u s
r e s u l t s as to the a t o m i c p r o p o r t i o n s . Secondly, few
intermetallic crystals, either natural or synthesized,
w e r e of a s i z e which p e r m i t t e d g o n i o m e t r i c e x a m i n a tion to s u p p o r t s u s p e c t e d f o r m a t i o n of unique c r y s t a l line s p e c i e s . F i n a l l y , in c a s e s w h e r e c a r e f u l w o r k
and v e r i f i c a t i o n by independent a u t h o r s left little doubt
as to the e x i s t e n c e and t r u e c o n s t i t u e n c y of the c o m pound, it was s t a r t l i n g to find f o r m u l a e such as CusSi,
Ag3Lito and FeZn7 which c l e a r l y in no way c o n f o r m e d
to n o r m a l v a l e n c y r u l e s . W o r s e yet, it a p p e a r e d that
the v a l e n c y co n cep t f o r r a t i o n a l i z i n g compound f o r m u lation m i g h t not be a p p l i c a b l e at all, s i n c e a g ive n
m e t a l p a i r could ex h i b i t s e v e r a l d i f f e r e n t r a t i o s e.g.
KI-Ig, KHg2, KHg3, K2Hg9 and KHgxo.
A n o t h e r p r o b l e m e n c o u n t e r e d was the a p p a r e n t a b i l ity of s o m e compounds to e x i s t o v e r a r a n g e of c o m p o s i t i o n s ( s e v e r a l p e r c e n t in many c a s e s ) and not j u s t
at s o m e s p e c i f i c s t o i c h i o m e t r i c r a t i o as with o r d i n a r y
s a l t s . It is i r o n i c that B e r t h o l l e t , 1~ w h i l e i n c o r r e c t
in his view of s i m p l e c h e m i c a l compounds and conf u sed with r e s p e c t to d i s t i n g u i s h i n g b e t w e e n m i x t u r e s ,
s o l i d s o l u t i o n s , a l l o y s and g l a s s e s , was p r e s c i e n t in
his a n t i c i p a t i o n of the v a r i a b l e c o m p o s i t i o n s e m i c o n ducting, i n t e r m e t a l l i c and n o n s t o i c h i o m e t r i c c o m pounds r e c o g n i z e d today. Indeed, it h as b e e n a r g u e d
that o v e r l y r i g i d a c c e p t a n c e of the D a l t o n i a n p i c t u r e
in the n i n e t e e n t h c e n t u r y has c o n s t i t u t e d a s i g n i f i c a n t
s e t b a c k to m e t a l l u r g i c a l c o n s t i t u t i o n and so l i d s t a t e
c h e m i s t r y . Th e Daltonian concept of the a t o m i c p r o p o r t i o n a t i o n of compounds so i m b u e d the thinking of
VOLUME 8A,SEPTEMBER 1977-1339
a l l i n v e s t i g a t o r s of t h e s o l i d s t a t e t h a t i t w a s e x t e n d e d
t o a l l o y s w h e n it s h o u l d n o t h a v e b e e n a n d p e r s i s t e d
d e s p i t e m u c h e v i d e n c e to t h e c o n t r a r y of t h e f o r m a t i o n
o f s o l i d s o l u t i o n s and n o n s t o i e h i o m e t r i e c o m p o u n d s .
P u t a n o t h e r w a y , t h e f o c u s of n i n e t e e n t h c e n t u r y s c i e n c e w a s o n t h e m o l e c u l e a n d c r y s t a l s w e r e t h o u g h t of
a s m a d e up o f m o l e c u l e s - h e n c e , t h e d i f f i c u l t y w i t h
solid solutions and nonstoichiometric compounds. Today we v i e w the whole c r y s t a l in a s e n s e as a m o l e cule and therefore can accommodate solid solutions
and off-stoichiometric compositions.
D e s p i t e the d i f f i c u l t i e s d i s c u s s e d above, p r o g r e s s
w a s m a d e - b y b e i n g a w a r e of t h e s o u r c e s of e r r o r a n d
by e m p l o y i n g s e v e r a l e x p e r i m e n t a l m e t h o d s in c o n c e r t
r a t h e r t h a n r e l y i n g o n o n e a l o n e . A s a r e s u l t , N e v i l l e ~~
w a s a b l e to r e p o r t i n 1900 a t a b u l a t i o n o f t h i r t y - s e v e n
c o n f i r m e d c o m p o u n d s a n d by 1914, a t o t a l of 263 c o u l d
b e l i s t e d b y D e s c h 1~ w h o s e p o r t r a i t i s s h o w n in F i g .
20. It w a s b y t h e n c l e a r t h a t t h e p r o b l e m s of t h e g e n e r a l i n a p p l i c a b i l i t y of n o r m a l v a l e n c e r u l e s a n d of
s t o i c h i o m e t r i c d e v i a t i o n w e r e r e a l and would have to
be f a c e d by f u r t h e r r e s e a r c h . Thus e v o l v e d the m o d e r n c o n c e p t i o n of i n t e r m e t a l l i e c o m p o u n d s as a d i s t i n g u i s h a b l e f a m i l y of m a t e r i a l s , f r e q u e n t l y p o s s e s s i n g m a n y o f t h e c o m m o n m e t a l l i c a t t r i b u t e s of l u s t e r
a n d c o n d u c t i v i t y , b u t w i t h e a c h m e m b e r r e s t r i c t e d to
c e r t a i n r a n g e s of c o m p o n e n t c o m p o s i t i o n and e x h i b i t ing unique p r o p e r t i e s , not r e a d i l y p r e d i c t a b l e f r o m
t h o s e of t h e c o m p o n e n t s . ~
Phase Diagrams
Perhaps no other developmenthas contributed so
much to our rationalization of the occurrence and behavior of intermetallic compounds as the phase diagram. Apart from its theoretical basis and applications, its value as a constitutional "road map" is now
so well appreciated that it is difficult to realize that
it wasn't always there-both as a conceptual tool and
as an experimental record for the most common alloy
systems. The first sytematic study of the freezing behavior of an alloy system was done in 1829/30 by
Frederik Rudbergs7 who studied the systems Pb-Sn,
Sn-Bi, Zn-Sn, Pb-Bi, Bi-Zn as well as the ternary
Pb-Sn-Bi alloys to some extent. He measured the
time required for a given weight of alloy to cool
through 10~ intervals, i.e. the data were obtained
for what is now called an inverse cooling rate curve.
A l t h o u g h h e m a d e n o g r a p h i c a l p l o t of h i s d a t a f o r t h e
P b - S n s y s t e m , h e w a s a b l e to e s t a b l i s h t h a t t h e a l l o y s ,
unlike the p u r e m e t a l s , exhibited two t h e r m a l a r r e s t s
*To Deschfallsthe credit for producingthe first monographm4on mtermetalhc
compounds.Curiously, another monographwas pubhshedby a pair of Itahan
authors, Gius and Gma,msvery shortly later. Despite the near simultaneity of
publicatmn, the two works are very complementaryand not at all redundant.
Gma and Gma include more than 800 referencescomparedto Desch's200. They
treat equdibrmm dmgramsextenswelyand the details of the specificsystems
studied thus far, while Deschconsidersmlcrostmcture,Isolation techmquesand
the ex,stenceof compoundsin the hquld state. Both volumescover thermal
analysis, physmalpropertiesand ternary compounds The Gma's made no original
research contnbutmns in the field insofar as this author has been able to discover
Desch, on the other hand, studied lsolatmn techniques,grain boundanesand the
properties of j3brass, althoughlntermetallicswere only a small part of his total
research pubhcatmns.See McCance m6 for a biographicalsketch of Desch and a
bibliography.
t"It is for this reason the writer prefersthe term "'intermetalliccompound" to
the alternaave "intermediatephase "'
1340-VOLUME 8A, SEPTEMBER 1977
on solidification-theupper variable with composition,
the lower constant-with the exception of a single composition which he called a "chemical alloy". This
composition he found froze at a single temperature,
the same as the constant lower temperature for the
other alloys. The invariant temperature (187~ and
composition (75 at. pct Sn) he found are very creditably
close to modern values for what we now know as the
Pb-Sn eutectic (183~ 73.9 at. pct). Rudberg's work
has been discussed and warmly appreciated in a recent article by Prince.I~ However, Prince does not
recognize that independentand virtually simultaneous
work on the Pb-Sn system was carried out by KupfferI~
at the St. Petersburg Polytechnic Institute, although
the accuracy of Kupffer's results was not as good as
Rudberg's.
Over the next several decades, other systematic
studies of freezing behavior of binary alloys were
made, but not until Roberts' studyI~ of the Cu-Ag system in 1875 was any graphical representation was
made of the results and not until the work of Stansfield, n~ an associate of the same author (who now
styled himself: Roberts-Austen) on Cu-Sn in 1895 did
a diagram appear containing an intermetallic compound (See Fig. 21). It will be noted that while both
the liquidus and solidus curves are drawn approximately correctly, and while some of the physical property measurements indicate the likely location of intermetallic phases, there is really almost no detail
in the solid part of the diagram. Curiously, the
earliest diagram I have been able to find which explicitly acknowledges the presence of intermetallic
compounds in the system is that of Wright et al n l on
:,~
or162
Fig. 20-Portrait of Cecil H. Desch (1874-1959). (J Inst Metals )
METALLURGICAL TRANSACTIONS A
ALLOYS
C.
L
/'late
RESEARCH.
E
" I$Z"
I
$32"
4,7Z ~
112"
y~
75~."
392"
a2"
Co1,?-~ IOO
60
80
~10
70
',60
:
:,50
70
80
20
H :
W R I G H T , et al - - 1891
.~t lweP
Ztnc
(a)
SEITH, HELMHOLD
to
:'~.
.
- - 1951
ao
.
.
p~
~.
z~
(ll)
Fig. 2 2 - I s o t h e r m a l section o f the Pb-Ag-Sn s y s t e m (a) at 8 0 0 ~ b y
Wright et al 1H ( 1 8 9 1 ) and (b) at 7 5 0 ~ b y Seith and H e l m h o l d H2
(1951).
METALLURGICAL TRANSACTIONS A
90
10
/~rot
I00 T~
0 p ~ c~,~
Fig. 21 F r e e z i n g p o i n t s and various physical p r o p e r t i e s of coppertin alloys as a f u n c t i o n of comp o s i t i o n as p l o t t e d by Stansfield. 110 The freezing p o i n t data
are his own, the e m f curve was
t a k e n from the w o r k o f Laurie,
the electrical c o n d u c t i v i t y curve
from t h a t o f Lodge, the i n d u c t i o n
balance curve from t h a t of
R o b e r t s - A u s t e n and the t h e r m a l
conductlvxty from t h a t o f Calvert
and J o h n s o n (see Stansfield for
references). F r o m these results
and others, Stansfield d e d u c e d the
existence o f four or five different
copper-tin c o m p o u n d s .
Coneluchvl~l'--
the t e r n a r y s y s t e m , P b - A g - Z n , * shown in F i g . 22(a).
In this i n s t a n c e he is p l o t t i n g f o r an i s o t h e r m the t i e l i n e s in the t w o - l i q u i d r e g i o n b e t w e e n the l e a d - r i c h
p h a s e and the s i l v e r / z i n c - r i c h p h a s e a l o n g the o p p o s i t e
edge of the s y s t e m . ~ $ T h e d e t a i l e d s h a p e of the c u r v e
l e d W r i g h t to d e d u c e the p r e s e n c e of two i n t e r m e t a l l i c
p h a s e s , now known a s the ~ and E p h a s e s in the A g - Z n
s y s t e m . F i g u r e 22(b), t a k e n f r o m m o d e r n w o r k zz2 on
the s a m e s y s t e m a l m o s t 60 y e a r s l a t e r , s h o w s the
e s s e n t i a l c o r r e c t n e s s of W r i g h t et al's r e s u l t .
F r o m the t u r n of the c e n t u r y on, p h a s e d i a g r a m s b e gan to a c c u m u l a t e r a p i d l y in the l i t e r a t u r e with the
r e s u l t shown in F i g . 23 of the c u m u l a t i v e t o t a l n u m b e r of b i n a r y s y s t e m s f o r which at l e a s t a p a r t i a l d i a g r a m had b e e n p u b l i s h e d . (We s h a l l r e t u r n below to a
d i s c u s s i o n of the s i g n i f i c a n c e of this c u r v e . ) It i s notew o r t h y that no one s c h o o l c o n t r i b u t e d m o r e to the d e t e r m i n a t i o n of p h a s e d i a g r a m s on m e t a l l i c s y s t e m s
than t h a t at GSttingen h e a d e d b y G u s t a v T a m m a n n
whose p o r t r a i t is shown in F i g . 24. It is r e m a r k a b l e
too that t h i s was no r u d d e r l e s s d a t a - g a t h e r i n g f o r a y
into m e t a l l u r g i c a l t h e r m o c h e m i s t r y but was a w e l l d e s i g n e d s e r i e s of i n v e s t i g a t i o n s s p e c i f i c a l l y u n d e r t a k e n to p r o v i d e the b a s i s for an u n d e r s t a n d i n g of the
laws g o v e r n i n g the f o r m a t i o n of i n t e r m e t a l l i c s a s is
*The reason for the early interest in th~s system was, of course, the Parkes
process39 for recovery of Ag values during lead refining.
t It is interesting to note that this is apparently the first recorded instance of
the now standard method of representing the composition of ternary alloys on a
tnangular coordinate system. It was suggested to Wright by Stokes (in a note
accompanying Ref. 111) who m turn derived the idea from Maxwell's representation of the composztion of colors. Stokes' note is of particular significance in that
it defines such now well known terms as critical curee, tie-line and conjugate
alloys.
:~Cyril Smith (prwate communication) points out that, unknown to Stokes,
R. F. Thurston had previously utilized the same construction for representing the
compositional dependence of the strength properties of Cu-Zn-Sn alloys (Trans.
Amer. Soc CivilEng., 1881, vol. 10, p. 1 andProc. AAAS, 1881, vol. 26, p. 114)
The pronounced peaking of strength properties near the 3 brass composition was
very evident in Thurston's results, although he had no knowledge of the constitution of his alloys. Actually J. H. Gzbbs [Trans. Conn. Acad., vol. 3, p. 105, 187576] had even earher suggested this means of representation in his classm paper but
neither Stokes nor Thurston were aware of It.
V O L U M E 8A, S E P T E M B E R 1 9 7 7 - 1 3 4 1
10,000
of 82 Metals
. . . . . . . Max.
. . . . . No.
. . . .of
. . Binary
. . . . . . .Combmations
....
HansenSequelae ~ f
NO. of 1,000
Hansen~
f,
Systems
Bornemann_~l
Studied
lLaves
I 'Geometrical
I
Fac;~'s'- -"
Roozeboom-~ [ Hume-Rotherymee
100
Rudberg
Kupffer
Gibbs
1
' ~
'
1800
1825
1850
/
~,I
~ATammann >100 Diagrams
/ " tl st Intermetalhc
I Shown,
1875 1900
Year
1925
L
1950
1975
Fig. 23-Chronological growth in the number of binary metallic phase
diagrams studied. The points on the curve are derived from analysis of
the Houghton/Prince bibliography~is and from counts reported by
Prince116from the compilations of Hansen and its sequelae. Notations
above the curve refer to significant events in the history of phase diagrams, those below cite similarly important milestones in the history
of intermetalllc compounds.
n i n e t e e n t h c e n t u r y as knowledge of the c o n s t i t u t i o n of
a l l o y s was building, i n s t a n c e s w e r e found of i n t e r m e t a l l i c compounds with c o n g r u e n t m e l t i n g points
g r e a t e r than those of e i t h e r component m e t a l , compounds f o r m e d by p e r i t e c t i c r e a c t i o n s , o t h e r s that
d e c o m p o s e d eutectoidally, and solid s o l u t i o n s that
somehow d e c o m p o s e d to f o r m compounds. M o r e o v e r ,
a p a r t f r o m e l u c i d a t i o n of the conditions of f o r m a t i o n
of compounds, this body of s y s t e m a t i c work c o n f i r m e d
the d i s t r e s s i n g r e s u l t s of e a r l i e r s c a t t e r e d work on
i n t e r m e t a l l i c s - n a m e l y that they often extended over
a r a n g e of c o m p o s i t i o n s , that this r a n g e s o m e t i m e s
failed to include a s i m p l e s t o i c h i o m e t r i c r a t i o , and
that even when s i m p l e r a t i o s did obtain they were
s e l d o m those to be a s s o c i a t e d with n o r m a l v a l e n c i e s
and a given p a i r of m e t a l s could often exhibit d i f f e r e n t
a p p a r e n t v a l e n c i e s in the s a m e s y s t e m .
We now t u r n to e x a m i n a t i o n of some of the f a c t o r s
which s t a b i l i z e i n t e r m e t a l l i c c o m p o u n d s . Two groups
of these, e l e c t r o n i c f a c t o r s and g e o m e t r i c f a c t o r s ,
each s u b s u m e s e v e r a l d i s t i n c t i d e a s . Hence, our
focus m u s t again n e c e s s a r i l y n a r r o w to a c o n s i d e r a tion of two of the m o s t i m p o r t a n t ideas, one in each
group, e l e c t r o n c o n c e n t r a t i o n and r a d i u s r a t i o of the
atomic c o m p o n e n t s , s
Electron Concentration
Fig. 24 Portrait of Gustav Tammann (1861-1938). (Z Metallk
made c l e a r in a v e r y e a r l y p a p e r by T a m m a n n ) ~3
G a r n e r ~4 has provided us with a c o m p r e h e n s i v e app r e c i a t i o n of T a m m a n n ' s work and an e n t e r t a i n i n g
b i o g r a p h i c a l sketch.
E x p e r i m e n t a l l y , the study of alloy c o n s t i t u t i o n was
aided by the addition of e x a m i n a t i o n of the c o m p o s i t i o n - d e p e n d e n c e of p h y s i c a l p r o p e r t i e s by Matt h i e s s e n ~7'1z~ and of m e t a l l o g r a p h i c e x a m i n a t i o n by
S o r b y ) ~9 On the t h e o r e t i c a l side, the a p p l i c a t i o n of
G i b b s ' p r i n c i p l e s of phase e q u i l i b r i a to m e t a l l i c s y s t e m s was s u g g e s t e d by J u p t n e r ~2~ and by Le C h a t e l i e r ~2~
and effectively d e m o n s t r a t e d by Roozeboom 122 in a
famous p a p e r in 1900. In these l a s t d e c a d e s of the
1342 VOLUME 8A, SEPTEMBER 1977
H u m e - R o t h e r y ' s f a m o u s 1926 paper ze5 p r o p o s i n g
e l e c t r o n s t a b i l i z a t i o n of p h a s e s is the f o r m a l p u b l i c a tion of the a u t h o r ' s d o c t o r a l t h e s i s , the work for which
was c a r r i e d out i n the y e a r s 1922-25. The p a p e r cons i s t s of five p a r t s : I) a d i s c u s s i o n of the a p p l i c a t i o n
of the p h a s e r u l e to m e t a l l i c s y s t e m s c o n t a i n i n g i n t e r m e t a l l i c compounds; II) and III) d i s c u s s i o n s of the
n a t u r e of i n t e r m e t a l l i c compounds and of m e t a l l i c
p h a s e s of v a r i a b l e composition; and IV) and V) e x p e r i m e n t a l s t u d i e s of e q u i l i b r i a in the C a - S n and Mg-Sn
s y s t e m s , together with a note on the s y n t h e s i s of
Na2Sn. The s e m i n a l i d e a - t h a t the s t a b i l i t y of c e r t a i n
i n t e r m e d i a t e p h a s e s i s d e t e r m i n e d by the e l e c t r o n to
atom r a t i o - a p p e a r s in P a r t III. It is noteworthy that
this concept is not deduced by e l a b o r a t e m a t h e m a t i c a l
a r g u m e n t o r even f r o m his own e x p e r i m e n t s but r a t h e r
is an o r i g i n a l i n s i g h t d r a w n f r o m data in the work of
o t h e r s . It should also be o b s e r v e d that the concept was
f i r s t applied only to the/3 p h a s e s with e / a = 3/2: ext e n s i o n to the y p h a s e s with r a t i o s of 21/13 and c
p h a s e s with 7 / 4 came l a t e r ; (see F i g . 25). H u m e R o t h e r y was not the f i r s t to draw a t t e n t i o n to the
s i m i l a r i t y of the phase d i a g r a m s of the a l l o y s of Cu,
Ag, and Au with Zn, Cd, A1 and Sn. O t h e r s , most
notably C a r p e n t e r , 126 had done this a decade e a r l i e r .
Nor was the X - r a y evidence yet at hand p r o v i n g the
s t r u c t u r a l i s o m o r p h i s m of the b e t a p h a s e s . A n d r e w s x27
and Owen and P r e s t o n ~28 had shown CuZn to have the
bcc s t r u c t u r e ; and H u m e - R o t h e r y i n f e r r e d that the/3
Cu-A1 phase, Cu3A1, was also bcc f r o m the s i x - f o l d
W i d m a n s t ~ t t e n p a t t e r n exhibited by the ot p r e c i p i t a t i o n .
With this s l i m s t r u c t u r a l b a s e , and knowing f u r t h e r
only that the f i r s t i n t e r m e d i a t e p h a s e s in the c o p p e r b a s e s y s t e m s a p p e a r e d n e a r the CuZn, Cu3A1 and
CusSn c o m p o s i t i o n s , H u m e - R o t h e r y took a giant m e n t a l
leap and p r o p o s e d that these p h a s e s a p p e a r e d b e c a u s e
*For an extendedtreatmentof the basesfor stab]hzauonof mtermetalhc
structuressee the texts by Barrett and Massalsk1123and by Pearson.T M
METALLURGICALTRANSACTIONSA
a
//re
Cu-Zn
Ag-Zn
.9 9
Au-Zn ~ _
BBI_I
Cu-Be
9
I__
Cu-AI
Ag-Cd
Ag-A,
l
I
Cu-Sn
I
Ag -S n
II
I
9
Ni-Sn
1.36 1-5 1-615 1-75
Electron Concentration
Fig. 2 5 - T a b l e o f t h e o c c u r r e n c e o f e l e c t r o n c o m p o u n d s as n o t e d m
early research.
of a favorable valence e l e c t r o n to atom r a t i o of 3/2
and p r e d i c t e d that these and s i m i l a r Ag and Au compounds would be i s o m o r p h o u s . A f t e r his p a p e r had
been submitted, but before publication, t h r e e independent confirmations a p p e a r e d ! X - r a y studies by W e s t gren and P h r a g m e n 129 proved the isomorphous nature
of the t h r e e Zn/3 phases, Murphy ~3~ found a Ag-Sn/3
at Ag~Sn and Stockdale T M d e t e r m i n e d that t e r n a r y ~3's
in the Cu-A1-Sn s y s t e m were fixed at e/a r a t i o s of
3/2. What g r e a t e r r e w a r d could a young m e t a l l u r g i s t
hope for f r o m his f i r s t m a j o r publication!*
Space does not p e r m i t a full recounting of subsequent
developments of the e l e c t r o n concentration c o n c e p t the r e a l i z a t i o n that alloy s t r u c t u r e s due solely to its
o p e r a t i o n a r e a r a t h e r s m a l l c l a s s , the c o r r e l a t i o n
of the e/a r a t i o idea with the energy band s t r u c t u r e of
m e t a l s (once s t r a i g h t - f o r w a r d , but now a d m i t t e d l y
complex), and the understanding that in the c r y s t a l
c h e m i s t r y of alloys we usually o b s e r v e an i n t e r p l a y
of s e v e r a l different p r i n c i p l e s of which e l e c t r o n conc e n t r a t i o n is but one. Suffice it to say that the basic
idea of e l e c t r o n concentration has now been extended
to many different a r e a s : 134'135 solubility l i m i t s of t e r minal solid solutions, phase constitution of m u l t i c o m ponent alloys, the " P h a c o m p " method of f o r e c a s t i n g
the p r o p e n s i t y for s i g m a phase p r e c i p i t a t i o n in s u p e r a l l o y s and o t h e r s , including the p a r t i c u l a r p r a c t i c a l
applications of i n t e r m e t a l l i c compounds high-lighted
in the p r e s e n t p a p e r .
What w e r e the fundamental p i e c e s of understanding
or information that made p o s s i b l e H u m e - R o t h e r y ' s
g r e a t advance ? Although the i m p r o v e d p r e c i s i o n and
v a r i e t y of a v a i l a b l e e x p e r i m e n t a l techniques and the
i n c r e a s i n g l y s o p h i s t i c a t e d understanding of the m e t a l l i c state c e r t a i n l y contributed, it is r e a d i l y apparent
that the sine qua non's of this r e s e a r c h were a knowledge of the phase d i a g r a m s of the cited b i n a r y s y s t e m s and of the n o r m a l v a l e n c i e s of the m e t a l l i c e l e ments.
G e o m e t r i c a l A s p e c t s of
I n t e r m e t a l l i c Phase Stability~
The G r e e k p h i l o s o p h e r s of the a t o m i s t i c s c h o o l Leucippus, D e m o c r i t u s and E p i c u r u s - viewed m a t t e r
in t e r m s of t h r e e b a s i c postulates which could be
d e m o n s t r a t e d to be l o g i c a l l y sound and c o n s i s t e n t
with o b s e r v a b l e facts. These were:
~,Jgr
a) Atoms a r e the ultimate constituents of matter;
t h e i r size, form, configuration and combination v a r y
to constitute the d i v e r s i t y of substances in the world.
b) Atoms a r e capable of motion.
c) A void e x i s t s between a t o m s of a substance thus
p e r m i t t i n g atomic d i s p l a c e m e n t s and motions.
J,
[ll~[llk ~'
\
Fig. 2 6 - P o r t r a i t o f William t l u m e - R o t h e r y ( 1 8 9 9 - 1 9 6 8 ) . (Pros
A STM. )
METALLURGICAL TRANSACTIONS A
The G r e e k p h i l o s o p h e r s stopped short of showing
just how a t o m i c a r r a n g e m e n t s led to m a c r o s c o p i e a l l y
o b s e r v a b l e s t r u c t u r e s and p r o p e r t i e s in p a r t i c u l a r
c a s e s . The lack of both the t e m p e r a m e n t a l inclination
and the tools with which to e x p e r i m e n t l i m i t e d t h e i r
contribution to a b r i l l i a n t guess which could not be exploited. It is i m p o r t a n t h e r e to e m p h a s i z e that
" a t o m " has meant different concepts to different
people at different t i m e s . The G r e e k and C a r t e s i a n
atoms or c o r p u s c l e s were not the m o d e r n (nineteenth
century chemical) atom, but r a t h e r s m a l l p a r t i c l e s
*Hume-Rothery, whose portrait is shown in Fig. 26, was not to lose his interest
in mtermetalhc compounds and the soentlfiC basis of the constitution of alloys
throughout the next forty or so years of an exceedingly productive professional
career (178 publications and seven books). Raynor has gwen us both a biographical sketch and bibhography of Hume-Rothery's pubhcatlons ~a2 and a detailed
analysis of his contnbutions to the scmnce of alloy forrnatlon.133
t T h e introductory paragraphs of this section are based on the books by Berry s~
and Smith. 136
V O L U M E 8A, S E P T E M B E R 1 9 7 7 - 1 3 4 3
i n f e r r e d from the a p p e a r a n c e of f r a c t u r e d or cut s u r faces and extended by thought to a g e n e r a l explanation.
L a t e r the philosophical idea of absolute i n d i v i s i b i l i t y
b e c a m e paramount; yet D e s c a r t e s and now we moderns
deny this view.
After a p e r i o d of hundreds of y e a r s in which atomi s t i c concepts were out of vogue, in the seventeenth
century many w o r k e r s , including D e s c a r t e s , r e v i v e d
the d i s c u s s i o n of the s t r u c t u r e of m a t t e r and c o n t r i buted the c o r p u s c u l a r conception that t h e r e exist v a r i ous s t a t e s of aggregation of m a t t e r , c e r t a i n types of
p r o p e r t i e s being affected most s t r o n g l y by c e r t a i n
l e v e l s of aggregation. Meanwhile, Kepler, Hooke,
Huygens and o t h e r s speculated on the p o s s i b i l i t y of
r e g u l a r packings of s p h e r e s being the ultimate s o u r c e
for the o b s e r v e d m a c r o s h a p e s of n a t u r a l c r y s t a l s . Still
l a t e r (1775)Grignon 137 d e s c r i b e d a c r y s t a l l o g r a p h i c
model viewed by Smith ~36 as the f i r s t model of a
solid solution but which could equally well be taken as
a model of a b i n a r y i n t e r m e t a l l i c compound.
" I am p e r s u a d e d that having acquired an exact knowledge of the shape of the c r y s t a l s , or r a t h e r of the
m o l e c u l e s of each metal, one would be able to d i s cover (from the f o r m which would be taken by the
c r y s t a l s of s e v e r a l m e t a l s capable of union when
joined together) the kind of m e t a l which would make
an alloy, and the p r o p o r t i o n s of the mixture, by computing the opening and the number of the angles, and
the g r e a t e r or l e s s extension of the faces of the
h a l f - b r e e d c r y s t a l s (cristaux metis) of the alloyed
metals; b e c a u s e two bodies when united take together
a main configurational form which depends on t h e i r
proportions."
Throughout the nineteenth century, l i t t l e p r o g r e s s
was made with r e g a r d to i n t e r m e t a l l i c c r y s t a l s t r u c u r e s , both for lack of techniques and b e c a u s e suitable
c r y s t a l s were r a r e l y a v a i l a b l e . M i n e r a l o g i s t s were
building l a r g e compendia of data and finding many isomorphs and other b a s e s of s y s t e m a t i z a t i o n but only a
few i n t e r m e t a l l i c s occur as n a t u r a l m i n e r a l s . C r y s t a l s r e c o v e r e d f r o m melts were only r a r e l y sufficiently
r e g u l a r for t h e i r c r y s t a l l i n e c h a r a c t e r to be r e c o g nized and e x p e r i m e n t a l m e a s u r e m e n t s made. M i l l e r 92
(of c r y s t a l l o g r a p h i c indices fame) makes mention of
c r y s t a l s of CuSn in S t r a s s b o u r g ' s m i n e r a l o g i c a l collection in 1835 and c r y s t a l s of FeZn7 had been r e covered many t i m e s f r o m dipping baths, ~38 but these
were exceptions. In any event, t h e r e was enough s c a t t e r e d evidence to convince most that m e t a l s were
c r y s t a l l i n e but knowledge of s u b c r y s t a l l i n e s t r u c t u r e
was lacking. Speculative e m p h a s i s was placed on the
a r r a n g e m e n t of atoms in the molecule and not upon
the s p a t i a l r e l a t i o n s h i p s of the m o l e c u l e s t h e m s e l v e s .
C e r t a i n l y the modern view of the whole c r y s t a l as the
compound molecule was no p a r t of nineteenth century
thinking.
Despite the speculations of the G r e e k p h i l o s o p h e r s
m i l l e n i a e a r l i e r , in the nineteenth century techniques
w e r e s i m p l y not a v a i l a b l e for the d e t e r m i n a t i o n of
absolute values of the s i z e and r e l a t i v e d i s p o s i t i o n of
atoms and such questions had l i t t l e appeal. E x p e r i ments by p h y s i c i s t s on c a p i l l a r i t y , s u r f a c e films, and
the kinetic behavior of gases led to the not too s a t i s f a c t o r y conclusion that atomic and m o l e c u l a r d i m e n 1344
V O L U M E 8A. S E P T E M B E R 1977
sions lay in the range f r o m 0~ to 10 or 20A but the
a t o m i c s c a l e s t r u c t u r a l p i c t u r e could p r o c e e d no
f u r t h e r . Following L a n e ' s suggestion to F r i e d r i c h
in 1912 that X - r a y s should be d i f f r a c t e d by c r y s t a l s , 139
a powerful tool for quantitative attack was at hand. At
once, three different i s s u e s in m e t a l l o c h e m i s t r y were
r e s o l v e d : a l l o r d i n a r y m e t a l s were c r y s t a l l i n e * even
though t h e i r m a c r o form gave no obvious clue to t h e i r
i n t e r n a l o r d e r ; c r y s t a l s t r u c t u r e was a key d i s t i n g u i s h ing c h a r a c t e r i s t i c in c o m p a r i s o n of m e t a l l u r g i c a l
phases: and knowledge of the c r y s t a l s t r u c t u r e and c e l l
d i m e n s i o n s of e l e m e n t a l m e t a l s and i n t e r m e t a l l i c
compounds containing common or r e l a t e d e l e m e n t s
p e r m i t t e d compilation of a set of m e t a l l i c r a d i i , A
m o r e difficult p r o b l e m , that of deducing f r o m the intensity of the X - r a y r e f l e c t i o n s the identity and p o s i tion of individual atoms within the unit cell, was also
u l t i m a t e l y solved. The pioneering publications using
the X - r a y technique in i n t e r m e t a l l i c s t u d i e s a r e those
of Andrews ~27 (1921) on the Cu-Zn s y s t e m and on
H e u s l e r ' s alloy, the f i r s t c r y s t a l s t r u c t u r e d e t e r m i n a tion by P a u l i n ~ 3s on Mg2Sn (1923), t3ain's ~4~ demons t r a t i o n of long range o r d e r in Cu~Au (1923), and Golds c h m i d t ' s T M deduction and compilation of atomic r a d i i
(1928).
Studies of the c r y s t a l s t r u c t u r e of i n t e r m e t a l l i c
p h a s e s r e v e a l e d some s t r u c t u r e s i d e n t i c a l to those of
c l a s s i c a l ionic c r y s t a l s , o t h e r s a p p a r e n t l y i s o m o r phous with the common e l e m e n t a l m e t a l s , and many
many m o r e - novel types, some e x t r e m e l y complex.~
During the 1920's the number of confirmed i n t e r m e t a l l i c s for which s t r u c t u r a l data were a v a i l a b l e was
s t i l l too few to p e r m i t much intelligent speculation or
a n a l y s i s of underlying s t r u c t u r a l p r i n c i p l e s . The
build-up was r e m a r k a b l y fast, however: by 1932 T a m mann published a l i s t of 400 s p e c i e s for most of which
c r y s t a l s t r u c t u r e data were at hand. 14~
P e r h a p s the f i r s t to attempt a b r o a d g e n e r a l i z a t i o n
of g e o m e t r i c a l p r i n c i p l e s for i n t e r m e t a l l i c compound
f o r m a t i o n was Prof. F. Laves, (Fig. 27) o r i g i n a l l y
of GSttingen U n i v e r s i t y and l a t e r of the Swiss F e d e r a l
Institute of Technology in Zurich. He had had a g e n e r a l
i n t e r e s t in the g e o m e t r i c a s p e c t s of c r y s t a l s t r u c t u r e s
and published a long a r t i c l e in 1930 setting forth a
d e s c r i p t i v e taxonomy of s t r u c t u r a l elements.~4s In the
next decade both his own r e s e a r c h e s and those of
o t h e r s built up c o n s i d e r a b l e knowledge of the s t r u c t u r e s found in s i m p l e b i n a r y i n t e r m e t a l l i c compounds,
p a r t i c u l a r l y those of the ABe type. A l a r g e number of
these had the MgCu2, MgZn2 or MgNi2 s t r u c t u r e s , the
f i r s t two of which had been d i s c o v e r e d by F r i a u f 146'147
and the l a t t e r by Laves and Lohberg. ~48 Since the
close r e l a t i o n s h i p s between the t h r e e s t r u c t u r e s were
f i r s t pointed out by Laves, these have since become
known as L a v e s p h a s e s . In 1942 when some sixty-five
e x a m p l e s were known, Laves and Wallbaum x49 p r o posed that this group of s t r u c t u r e s r e p r e s e n t e d the
e x e r c i s e of another p r i n c i p l e for the f o r m a t i o n of int e r m e t a l l i c p h a s e s to supplement H u m e - R o t h e r y ' s
*A good revmw of pre-X-ray diffraction evidence for the crystallimty of metals
is gwen by Smith m Chapters 10 and 11 of h~s Hzstory o f Metallography. 136
t Samson ~42points out that it Is interesting that Pauling's pioneering paper ~4~
on the crystal structure determination of an intermetallic also presented some
prehmmary results on NaCd2, a structure that has still not been completely solved
but is known to contmn >1100 atoms/unit cell.
METALLURGICAL TRANSACTIONSA
u n d e r s t a n d i n g that this too is an over s i m p l i f i c a t i o n .
A t o m s in such s t r u c t u r e s a r e not t r u l y s p h e r i c a l n o r
do they exhibit a fixed size.* F u r t h e r m o r e , in m o s t
c a s e s of s t a b i l i z a t i o n of i n t e r m e t a l l i c s t r u c t u r e s , we
see an interplay between geometrical factors, electron
c o n c e n t r a t i o n f a c t o r s and e l e c t r o c h e m i c a l f a c t o r s as
shown s c h e m a t i c a l l y in Fig. 29.
If we t r y to a n a l y z e the conditions that made p o s s i ble L a v e s ' g r e a t c o n t r i b u t i o n , we a g a i n see that, as
i n H u m e - R o t h e r y ' s case, it was not a new technique,
a unique e x p e r i m e n t a l o b s e r v a t i o n , or a n a b s t r u s e
:
M :
It
:
~- ~y,
I
I
:
~
:
I
"" ~,
:
I
:
I
,z~r
i:
H :I
:I
V
V
V
V
V
V
V
V
V
9
A
A
Jk
~k
A
9
9
9
Fig. 28--Two-dimensional analogue of Laves' concept of space filling
represented by dxscs of two different sizes, above; compared to close
packed array of single size discs, below.
Fig. 27-Portrait of Fritz Laves (1906-
). (From A mer. Mineral. )
e l e c t r o n c o n c e n t r a t i o n r u l e , n a m e l y the g e o m e t r i c a l
i d e a s of space filling, s y m m e t r y and c o n n e c t i v i t y .
T h e s e i d e a s w e r e m o r e fully e x p r e s s e d in a r e v i e w
p a p e r ~5~ in the famous 1955 ASM s e m i n a r . In the light
of this conception, the p a r t i c u l a r r a t i o s of the e l e m e n t a l m e t a l s c o m p r i s i n g the compound, whether they
be s i m p l e o r complex, a r e to be u n d e r s t o o d i n t e r m s
of the g e o m e t r i c a l l y f a v o r e d p a c k i n g s afforded with
c e r t a i n c o m b i n a t i o n s of atom s i z e and c o m p r e s s i b i l i t y
and have not to do p r i m a r i l y with v a l e n c e c o n s i d e r a t i o n s . T h i s p a c k i n g concept is not r e a d i l y g r a s p e d
f r o m s k e t c h e s of r e a l 3-d s t r u c t u r e s , the g e n e r a l idea
can be a p p r e c i a t e d however f r o m a 2-d analogue as
shown i n Fig. 28.
The r o l e of g e o m e t r i c a l f a c t o r s i n i n t e r m e t a l l i c
compound f o r m a t i o n is now a p p r e c i a t e d to extend v e r y
widely indeed. Even the b a s i c motif of the L a v e s
p h a s e s t h e m s e l v e s , a d e n s e p a c k i n g of two d i f f e r e n t
s i z e s of a t o m s with only t e t r a h e d r a l i n t e r s t i c e s , has
s i n c e b e e n found by S a m s o n ~s~ to be c o m m o n to as
m a n y a s eighteen d i f f e r e n t i n t e r m e t a l l i c s t r u c t u r e s ,
s o m e of them exceedingly complex. I n t e r e s t i n g l y ,
these include the s t r u c t u r e s of the Nb3Sn and
Mo(Co, Si)2 compounds f o r m i n g the b a s i s of two of
the m o d e r n p r a c t i c a l d e v e l o p m e n t s d e s c r i b e d e a r l i e r ;
that of the third, SmCos is a r e l a t e d s t r u c t u r e . S i m u l t a n e o u s with the r e a l i z a t i o n of the extent of the app l i c a b i l i t y of the g e o m e t r i c a l p r i n c i p l e s to the s t a b i l i z a t i o n of c e r t a i n i n t e r m e t a U i c p h a s e s has come the
METALLURGICAL TRANSACTIONS A
Fig. 29-Influence of the interaction of different stabilization factors
to create various crystal families of alloy phases (after Barrett and
Massalski 123).
*Pearson (Ref. 124, pp. 59, 74, and 137) has made an extremely interesting
suggestion that inverts, but in no way demeans Laves' concept. He adduces evidence to show that chemical bond, coordination or other geometrical factors
themselves influence structural dimensions and therefore the relative distances
between hgands in alloys, rather than that the formal sizes of the atoms themselves
mfluence structure type. Thus coordmatton requirements are met by mteratomm
distance adjustment (relative compressrun of component species) over a very
wide range of radius ratios of component species forming Laves structures.
VOLUME 8A, SEPTEMBER 1977-1345
theory which f o r m e d the take-off point. R a t h e r it was
that the a m a s s i n g of a c r i t i c a l volume of e x p e r i m e n t a l
data in the l i t e r a t u r e p e r m i t t e d an individual with
great insight to p e r c e i v e an underlying p a t t e r n not
p r e v i o u s l y apparent. In L a v e s ' case, his conception
would hardly have been p o s s i b l e , and confirmation out
of the question, had it not been for the p r i o r build-up
of phase d i a g r a m information (See Fig. 21) and c r y s t a l s t r u c t u r e data. Relevant too was a conscious or
unconscious limitation of attention to a s m a l l family
of compounds where the effect in question was likely
to be l e a s t p e r t u r b e d by the operation of other f a c t o r s .
Point Defects
The existence of compounds with extended c o m p o s i tional r a n g e s of s t a b i l i t y did not at f i r s t s e e m to pose
a p r o b l e m although the p r e v a l e n c e and i m p o r t a n c e of
this c l a s s was r e c o g n i z e d quite e a r l y by Guldberg 152
(1870) and Nasini a53 (1907). T h e r e was no way of investigating s t r u c t u r e at the level of a t o m i c - s c a l e and
a l l e a s e s of compounds of indefinite composition were
considered as solid solutions f o r m e d by the c o m pound. F u r t h e r m o r e , a g r a p h i c a l r e p r e s e n t a t i o n of
Gibbs' conception of the compositional dependence of
the free e n e r g i e s of neighboring p h a s e s in a s y s t e m as
in Fig. 30 showed c l e a r l y the t h e r m o d y n a m i c p o s s i b i l i t y for extended compositional r a n g e s of s t a b i l i t y of
a given phase, Beginning about 1900, t h e r m a l a n a l y s i s
and a n a l y s i s of r e s i d u e s following isolation of a s u s pected i n t e r m e t a l l i c began to be r e g u l a r l y supplemented by studies of the compositional dependence
of p h y s i c a l p r o p e r t i e s . This approach of " p h y s i c o c h e m i c a l a n a l y s i s " was p a r t i c u l a r l y championed by
N. S. Kurnakov,* whose p o r t r a i t is shown in Fig. 31.
and his students. One of the ma~or contributions of
this school was the d i s c o v e r y that in most c a s e s of
an extended compositional range, s i n g u l a r i t i e s were
r e v e a l e d on c o m p o s i t i o n - p r o p e r t y c u r v e s at points
usually c o r r e s p o n d i n g to simple a t o m i c p r o p o r t i o n s .
This finding led K u r n a k o v ~57 to take these s o - c a l l e d
Daltonian points as evidence of the existence of a
c h e m i c a l individual. The r e m a i n i n g e a s e s which
showed no such s i n g u l a r i t y he called B e r t h o t l i d e s .
true i n d e t e r m i n a t e compounds. (Such t e r m s a r e no
longer in use.)
As e a r l y as 1919, Tammann 159 had suggested that in
i n t e r m e t a l l i c compounds of s t o i c h i o m e t r i c p r o p o r t i o n s
the component a t o m i c s p e c i e s might be a r r a n g e d in an
o r d e r e d s t r u c t u r e . This s u r m i s e was l a t e r shown by
Bain ~4~ to be c o r r e c t in an e a r l y X - r a y diffraction
study of Cu~Au and confirmed by B e c k e r and E b e r t ~6~
in other compounds. It gradually b e c a m e c l e a r that
Kurnakov's s e p a r a t i o n of Daltonide and Berthollide
compounds was a r t i f i c i a l and that the absence of
s i n g u l a r i t i e s in p r o p e r t y - c o m p o s i t i o n curves should
be m o r e p r o p e r l y a t t r i b u t e d to the absence of o r d e r ,
e.g. Ag3A1, or to the o c c u r r e n c e of the s t o t c h i o m e t r i c
*Kurnakov's contribuhons to science were legion and ]n a great diversity of
fields halurgy, analytical chemistry, phase equd]bna, mineralogy and phys;cal
metallurgy His interest m intermetallic compounds began with his 1899 paper, ~
continued throughout hJs life.time, and is still reflected m the works of h~s
students N. V. Ageev, I. I Komilov and E. M. Savltsku, present day leaders m
that field. A multitude of btograph,cal sketches and appreciations appear m the
Russian language. More accessible material of this sort are the papers of Kaufrnan
and Beck lss and Lepeshkov ls~ (m English) and Dlougatch Is7 (in French)
1 3 4 6 - V O L U M E 8A, SEPTEMBER 1977
Temperatu~
AB
Composition
Fig. 3 0 - S c h e m a t i c drawing showing the derivat]on of the phase diagram from the free energy curves for a h y p o t h e t i c a l b i n a r y s y s t e m
specifically illustrating the possibility of a broad c o m p o s i t i o n a l range
of s t a b l h t y for an i n t e r m e d m t e phase, AB.
,A
r
.11
'"
~
L ~
!
F]g. 31 - P o r t r a i t ot Nlkolat S. K u r n a k o v (1860-1941 ). ( F r o m Usp
Khirn )
METALLURGICAL TRANSACTIONS A
c o m p o s i t i o n b e y o n d the s t a b i l i t y l i m i t of the c o m pound, e.g. /3CuZn.
F o r a t i m e , an u n e x p l a i n e d a n o m a l y e x i s t e d in that
a given p r o p e r t y , s a y h a r d n e s s , would show a m a x i m u m at the s t o i c h i o m e t r i c c o m p o s i t i o n f o r s o m e c o m pounds and a m i n i m u m f o r o t h e r c o m p o u n d s . K o r n i l o v ' s s u g g e s t i o n 16~ that this might r e s u l t f r o m the
p a r t i c u l a r t e m p e r a t u r e at which the m e a s u r e m e n t s
w e r e m a d e was s u b s e q u e n t l y c o n f i r m e d by W e s t b r o o k . 162 Some t y p i c a l r e s u l t s a r e shown in F i g . 32;
o t h e r i n s t a n c e s have b e e n s u m m a r i z e d in a l i t e r a t u r e
r e v i e w . 163 T h e s e b e h a v i o r s a r e i n t e r p r e t e d in t e r m s
of the m i s o r d e r i n g i n e v i t a b l y i n t r o d u c e d with d e v i a t i o n
f r o m s t o i c h i o m e t r y , the m o s t highly o r d e r e d c o m p o s i tion. At low f r a c t i o n s of the m e l t i n g point, w h e r e the
d e f o r m a t i o n p r o c e s s p r o c e e d s p r i m a r i l y by s l i p , any
p e r t u r b a t i o n of the r e g u l a r c r y s t a l l a t t i c e a s a f f o r d e d
by the point d e f e c t s i n t r o d u c e d by d e v i a t i o n f r o m
s t o i c h i o m e t r y c o n s t i t u t e s an i m p e d i m e n t to s l i p , and
the m a t e r i a l i s s t r e n g t h e n e d . At high h o m o l o g o u s
t e m p e r a t u r e s , d e f o r m a t i o n i s d i f f u s i o n c o n t r o l l e d and
the p r e s e n c e of d e f e c t s t e n d s to enhance diffusion
r a t e s and hence i n c r e a s e the a m o u n t of d e f o r m a t i o n
o b t a i n a b l e for a given load and t i m e .
I n t e r e s t in a t o m i c point d e f e c t s (as c o n t r a s t e d to
e l e c t r o n i c d e f e c t s ) b e g a n in the m i d - 1 9 2 0 ' s when
F r e n k e l T M showed that, in p r i n c i p l e , e v e r y compound
at t e m p e r a t u r e s above a b s o l u t e z e r o should have a
c e r t a i n c o n c e n t r a t i o n of d e f e c t s . The f i r s t type of d e fect to be t r e a t e d in d e t a i l was t h a t c a u s e d by a c o m ponent a t o m m o v i n g f r o m its n o r m a l l a t t i c e s i t e to
occupy an i n t e r s t i t i a l p o s i t i o n . B e c a u s e of the n e a r
e q u i v a l e n c e in s i z e of m o s t m e t a l a t o m s , t h i s t y p e is
not u s u a l l y e n c o u n t e r e d in i n t e r m e t a l l i c s . The r e m a i n i n g t y p e s of s i m p l e d e f e c t s a r e i m p o r t a n t to int e r m e t a l l i c s and include v a c a n c i e s * (atoms o m i t t e d
1000
Homolgous temperature
~
,
100
Hardness
Kglmm 2
10
1
35
~
i
i
40
45
0.8
0.9
i
I
I
50 55
A/o Mg
i
60
65
Fig. 32-1nfluence of defect concentration (devlahon from stolchiometry) and homologous temperature on the hot hardness of CsC1
structure AgMg alloys. After Westbrook.~a2
*In ionic crystals, considerations of charge balance reqmre equal numbers of
vacancms to be developed on each sublattice. This type of disorder ]s referred to
as Schottky-Wagner disorder.
METALLURGICAL TRANSACTIONS A
7.0
\
~\?gJnterstitials
6.5
Density,
gm cm "3
6.0
~
\
AO "~
I
. P',.g** ~
~
Substitutions " ~ k
0 Grav,metric- wire
AWaterdisplacement-wire
v Waterdisp|acement-bugk
Mg Vacancies....---"~
.....
"~ i ' ~ g
Ag V a c a n c i e s ~
5.5
40
'
45
Substitutions
"~
~
\
50
Atomic % Mg
'
55
60
Fig. 33-Density of AgMg as a function of composition. Solid lines are
calculated densities from X-ray data using a substltional defect model.
Broken lines are for similar calculations using vacancy and interstitial
models. After Hagel and Westbrook.]6s
f r o m n o r m a l s i t e s ) and a n t i s t r u c t u r e d e f e c t s ( a t o m s of
one kind s u b s t i t u t e d on s i t e s of the o t h e r s p e c i e s ) .
T h e s e d e f e c t s m a y a r i s e f r o m an i n c r e a s e in t e m p e r a ture, deviation from stoichiometry, radiation treatment, a change in the p a r t i a l v a p o r p r e s s u r e of one
of the c o m p o n e n t s in the a m b i e n t gas, a t e n d e n c y to
m a i n t a i n a c e r t a i n e/a r a t i o o r f r o m the p r e s e n c e of
a f o r e i g n s p e c i e s . F u r t h e r , m o r e than one type of d e f e c t m a y b e p r e s e n t s i m u l t a n e o u s l y , and d e f e c t s do
not n e c e s s a r i l y e x i s t a s r a n d o m i s o l a t e d d e f e c t s but
m a y be p a i r e d with o t h e r d e f e c t s , a r r a n g e d in c l u s t e r s , chains o r p l a n a r a r r a y s , o r c o n s t i t u t e a s u b l a t t i c e of t h e i r own. T h i s r i c h c o m p l e x i t y of a t o m i c s c a l e s t r u c t u r e has given r i s e to an e n t i r e s u b d i s c i p l i n e in s o l i d s t a t e c h e m i s t r y .
A f i r s t r e q u i r e m e n t to u n d e r s t a n d i n g the p o s s i b l e
e f f e c t s of d e f e c t s t r u c t u r e s i s to d e t e r m i n e the t y p e
of d e f e c t p r e s e n t . F o r i n t e r m e t a l l i c c o m p o u n d s , d e v i a t i o n s from stoichiometry (i.e. d e f e c t c o n c e n t r a tions) a r e u s u a l l y s u f f i c i e n t l y l a r g e that the d e f e c t
t y p e can b e d e d u c e d f r o m c o m p a r i s o n of X - r a y and
bulk d e n s i t i e s . An e x a m p l e f r o m the a u t h o r ' s w o r k 165
is shown in F i g . 33. F o r low d e f e c t c o n c e n t r a t i o n s ,
when m o r e than one d e f e c t t y p e i s p r e s e n t o r w h e r e
defect complexes exist, property measurements ref l e c t i n g a t o m m o t i o n (such a s diffusion o r i n t e r n a l
f r i c t i o n ) , e l e c t r o n m o t i o n (such a s r e s i s t i v i t y o r t h e r m o e l e c t r i c power) o r r e s o n a n c e e f f e c t s (such a s NMR
o r ESR) m u s t be c a l l e d into p l a y .
Although the a d v a n c e s in our u n d e r s t a n d i n g of c o m pounds having e x t e n d e d r a n g e s of c o m p o s i t i o n a l s t a b i l i t y have b e e n r e m a r k a b l e in the c e n t u r y s i n c e G u l d b e r g , t h i s has not come about by any b r e a k - t h r o u g h
by a s i n g l e i n v e s t i g a t o r . R a t h e r , it has r e s u l t e d f r o m
the s t e a d y a c c r e t i o n of knowledge in s m a l l s t e p s b y
m a n y d i f f e r e n t c o n t r i b u t o r s - b o t h t h e o r e t i c i a n s and
experimentalists.
Grain Boundaries
D e v e l o p m e n t of m o d e r n day c o n c e p t i o n s of the
s t r u c t u r e of s o l i d m e t a l s at the l e v e l of light m i c r o s copy was a v e r y long t i m e in c o m i n g . W h i l e on the
one hand t h e r e w e r e s o m e v e r y e a r l y o b s e r v a t i o n s of
VOLUME 8A, SEPTEMBER 1977- 1347
Fig. 34 Separated grains of an AgMgsample disintegrated by action of
nitrogen at 700~ After Westbrook and Wood.IS~
the a p p a r e n t c r y s t a l l i n i t y of m e t a l s , f a i l u r e to make
the p r o p e r d i s t i n c t i o n (now so c l e a r ) b e t w e e n cast
d e n d r i t e s , the g r a i n s of an a n n e a l e d m i c r o s t r u c t u r e
and i d i o m o r p h i c i n t e r m e d i a t e p h a s e s in alloys c o n t r i buted much to the delay. Even the i n t r o d u c t i o n of opt i c a l m e t a l l o g r a p h i c t e c h n i q u e s by Sorby ~66 in 1864 did
not i m m e d i a t e l y set m a t t e r s aright,* for c r y s t a l l i n i t y
was not only difficult to p r o v e u n d e r m a n y c i r c u m s t a n c e s but t h e r e was a l s o i n d i s p u t a b l e e v i d e n c e such
a s the m a r k e d d e f o r m a b i l i t y of m e t a l s , even by ext r u s i o n , that then a r g u e d s t r o n g l y for a highly v i s c o u s
but a m o r p h o u s c h a r a c t e r . As late as 1912 G u e r t l e r ~72
s t i l l found it n e c e s s a r y to e m p h a s i z e his b e l i e f in the
i n h e r e n t c r y s t a l l i n i t y of m e t a l s , and the notion of a
l o c a l l y l i m i t e d e x i s t e n c e of a m o r p h o u s m e t a l ( B e i l b y ' s
p o l i s h i n g l a y e r ~73 and R o s e n h a i n ' s i n t e r g r a n u l a r a m o r phous c e m e n t s x74) p e r s i s t e d for a n o t h e r decade or so.
Even g r a n t i n g s o m e f u z z i n e s s in the s t r u c t u r a l conceptions of solid m e t a l s into which the o b s e r v a t i o n s
had to be placed, two notable c h a r a c t e r i s t i c s of g r a i n
b o u n d a r i e s in i n t e r m e t a l l i c p h a s e s w e r e r e m a r k e d
v e r y e a r l y on. F i r s t was the m a r k e d i n t e r g r a n u l a r
e m b r i t t l e m e n t that s e e m e d to be m a x i m i z e d at i n t e r metallic compositions under certain circumstances.
G e o f f r o y ' s eighteenth c e n t u r y i n v e s t i g a t i o n of the alloys
of copper and zinc ~Ts included o b s e r v a t i o n s on f r a c t u r e
b e h a v i o r s which d i s t i n g u i s h e d (as we now see) b e t w e e n
the alpha, b e t a and g a m m a p h a s e s . C o m m e r c i a l use
was e v e n made of this fact in that b r a z i e r ' s s o l d e r e s s e n t i a l l y a p u r e b e t a b r a s s - w a s at one t i m e o r d i n a r i l y p r e p a r e d by pounding the solid alloy while
w a r m to s e p a r a t e it into the i n d i v i d u a l grains.~76 While
undoubtedly i n s o m e i n s t a n c e s such b e h a v i o r was occ a s i o n e d by the p r e s e n c e of second p h a s e s along g r a i n
b o u n d a r i e s , the s a m e r e s u l t obtains in m o s t c a s e s
even in a p h a s e - p u r e s p e c i m e n .
The second o u t s t a n d i n g c h a r a c t e r i s t i c of i n t e r m e t a l l i c g r a i n b o u n d a r i e s r e l a t e s to t h e i r c h e m i c a l
*DespiteSorby'searlypublicatmnof his findings,descnptmnof his techniques
and exhibitionof his photomicrographs,opttcat metallographydid not take
hold as a majormvestmgatwetechniqueuntd after Sorby'spapersof 1886/7.167-68
For a further descriptmnand analysissee Smith~69and the contrlbutmnsof
HighamZ7~and HumphriesIT1to the SorbyCentenmalSymposium.
1348-VOLUME 8A, SEPTEMBER 1977
k i n e t i c b e h a v i o r . E x p o s u r e of beta b r a s s to m e r c u r y
r e s u l t s in a n e x t r a o r d i n a r i l y r a p i d s e p a r a t i o n into
i n d i v i d u a l g r a i n s , x77 P l a t i n u m - l e a d alloys ( p r e s u m a b l y
c o n t a i n i n g the compound P t P b and p e r h a p s o t h e r s )
w e r e o b s e r v e d to d e c o m p o s e in a i r v e r y r a p i d l y while
p l a t i n u m was i n e r t and lead oxidized only v e r y slowly
u n d e r the s a m e c o n d i t i o n s . 178 C e r t a i n n i c k e l - a l u m i n i d e s w e r e found by S p e r r y 179 in 1899 to s i m i l a r l y
d i s i n t e g r a t e quickly in a i r even though the c o m p o s i tion itself is v e r y oxidation r e s i s t a n t , and we have
p r e v i o u s l y noted Hogg's o b s e r v a t i o n of the d i s i n t e g r a tion of MnA1. 45 Such b e h a v i o r has s i n c e b e e n found to
be g e n e r a l for s e v e r a l d i f f e r e n t c l a s s e s of i n t e r m e t a l l i c compounds.* An i l l u s t r a t i o n of the p h e n o m e n o n
is shown i n Fig. 34.
Unlike the c a s e of many other f a c t o r s reviewed, we
cannot point to a single p a p e r or group of p a p e r s that
can be said to c o n s t i t u t e a b r e a k t h r o u g h on this i m p o r t a n t p r o b l e m of the a n o m a l o u s c h a r a c t e r i s t i c s of
g r a i n b o u n d a r i e s in i n t e r m e t a l l i c compounds. Our
i n c r e a s i n g l y s o p h i s t i c a t e d u n d e r s t a n d i n g of g r a i n
b o u n d a r i e s in g e n e r a l ls2 and r e c e n t e l e c t r o c h e m i c a l 18~
and m i c r o h a r d n e s s 184 s t u d i e s c o n f i r m i n g the u n u s u a l
n a t u r e of g r a i n b o u n d a r i e s in p h a s e - p u r e i n t e r m e t a l l i c s
e m p h a s i z e the i m p o r t a n c e of t h e i r c o n t r o l in any
p r a c t i c a l a p p l i c a t i o n of i n t e r m e t a l l i c compounds. An
e x a m p l e f r o m the a u t h o r ' s work is shown in Fig. 35.
G r a i n b o u n d a r y h a r d e n i n g in M g - r i c h AgMg, a p p a r ently a s s o c i a t e d with m i n o r a m o u n t s of oxygen ancb/or
n i t r o g e n , can be c o r r e l a t e d with e m b r i t t l e m e n t c o r r e s p o n d i n g to a 400~ shift in d u c t i l e / b r i t t l e t r a n s i tion t e m p e r a t u r e . O t h e r work has shown that this effect is quite g e n e r a l for i n t e r m e t a l l i c s c o n t a i n i n g a n
o x y g e n - a v i d e l e m e n t . ~so,18~ However, the r e a s o n for
the m a r k e d change in b e h a v i o r with so slight a d e v i a tion f r o m s t o i c h i o m e t r y is not c l e a r . P a n i n and
F a d i n ~86 b e l i e v e that the d i s o r d e r e d n a t u r e of the g r a i n
b o u n d a r y r e g i o n in i n t e r m e t a l l i c compounds m u s t both
i n c r e a s e the effective s o l u b i l i t y of these r e g i o n s f o r
i n t e r s t i t i a l s p e c i e s (e.g. 0 or N) and s i m u l t a n e o u s l y
affect the g r a i n b o u n d a r y diffusivity of t h e s e e l e m e n t s ,
although they do not develop an explicit model by which
such effects could induce the o b s e r v e d local h a r d e n i n g
and e m b r i t t l e m e n t . Den B r o e d e r and Z i j l s t r a ~s7 note
200
100
Transition
Temperature
oC
Ag Mg
] ~
15
Annealed @ 300~
Relative ~ = 10
10
0
AH
5
AH
(Boundary)
%
-1 O0
-200,
i
i
i
44
46
,
?
i
J
48
50
L
I
52
AIo Magnesium
Fig. 35 Effect of stoichiometry on the ductile-b•tle transition temperature and grain boundary hardening in oxygen-segregatedAgMg
alloys. After Westbrook and Wood.18s
*The anomalousintergranulardisintegrationof intermetalhccompoundshas
becomeknownas the "pest" effect. For a rewew,somenew data and interpretation see Westbrookand Wood~~and Seyboltand Westbrook?8~
METALLURGICALTRANSACTIONSA
the s i m i l a r r e s p o n s e to t h e r m a l t r e a t m e n t of the coe r c i v e force in SmCo5 and grain boundary hardening
in CsC1 s t r u c t u r e compounds and suggest that both
may a r i s e f r o m grain boundary s e g r e g a t i o n of oxygen.
In the case of pure m e t a l s and solid solution alloys,
advances in our knowledge of grain boundaries have
come not so much f r o m m e a s u r e m e n t s of the effects of
grain s i z e on v a r i o u s m a c r o p r o p e r t i e s but r a t h e r f r o m
e x p e r i m e n t s d i r e c t e d at the p r o p e r t i e s of the bounda r y i t s e l f (or a v e r y local region n e a r the boundary)
e.g. e n e r g i e s , melting behavior, boundary composition,
mechanical p r o p e r t i e s , diffusivity, and so forth. F o r
i n t e r m e t a l l i c s , the only c o m p a r a b l e studies a r e the
e l e c t r o c h e m i c a l potential m e a s u r e m e n t s of Bakish
and Robertson 183 and the s e v e r a l m i c r o h a r d n e s s i n v e s tigations by W e s t b r o o k and a s s o c i a t e s ~s~
and
by Shaskov et al.188-19~ This p r o b l e m of the anomalous
behavior of i n t e r m e t a l l i c b o u n d a r i e s r e m a i n s one of
the g r e a t e s t i m p o r t a n c e both for s c i e n t i f i c u n d e r s t a n d ing and for p r a c t i c a l application.
ADDITIONAL COMPOUNDS WITH PRESENT OR
POTENTIAL APPLICATIONS
Although space will not p e r m i t a detailed review of
t h e i r h i s t o r i c a l development, s e v e r a l additional ins t a n c e s of the p r e s e n t or p r o j e c t e d applications of int e r m e t a l l i c compounds will be cited to i l l u s t r a t e the
r i c h d i v e r s i t y of pertinent p r o p e r t i e s . The r e f e r e n c e s
provide f u r t h e r d e t a i l s for the i n t e r e s t e d r e a d e r .
MnBi (Magnetooptical R e c o r d i n g Medium)
Magnetooptical r e c o r d i n g is a p a r t i c u l a r l y a t t r a c t i v e
option for computer s t o r a g e of information since it
combines the high bit d e n s i t y and redundancy potential
of optical methods with the e a s y e r a s a b i l i t y and t e m p o r a l s t a b i l i t y of magnetic methods. In c e r t a i n m a t e r i a l s , MnBi being the p r e e m i n e n t example, TM the ens e m b l e of p r o p e r t i e s is such that both b i t - b y - b i t and
holographic s t o r a g e can be envisioned. The d e s i r a b l e
p r o p e r t i e s a r e a l a r g e m a g n e t o c r y s t a l l i n e anisotropy,
l a r g e F a r a d a y rotation, low t h e r m a l conductivity, a
Curie t e m p e r a t u r e (T c) n e a r room t e m p e r a t u r e and a
high optical absorption. Writing is achieved by switching the magnetization of a thin film of the compound as
a r e s u l t of heating above T c caused by local light a b s o r p t i o n of an impinging l a s e r beam. Readout is obtained by the F a r a d a y rotation of the p o l a r i z a t i o n of
light t r a n s m i t t e d through or r e f l e c t e d from the film.
L a s e r beam excitation is r e q u i r e d b e c a u s e high r e s o l u tion writing r e q u i r e s that the n e c e s s a r y t h e r m a l pulse
be d e l i v e r e d in t i m e s s h o r t r e l a t i v e to the t h e r m a l
time constant of the film (~100 ns). Information is
e r a s e d by uniformly r e m a g n e t i z i n g the film in an ex-
Table II. Zr~l-Based Cladding
TensilePropertmsat 300~
UTS,MN/m2
Elongation,
Pct
Zr3A/Based
Zirc~doy-2(cw)
Zr-3.2Sn-l.lMo-1.1Nb
t 140
364
910
METALLURGICALTRANSACTIONSA
27
3
2
RA,Pct
27
55
56
t e r n a l magnetic field. L i m i t a t i o n s that must s t i l l be
o v e r c o m e to fully utilize the technique include the
low diffraction efficiency of h o l o g r a m s , humidity induced d e t e r i o r a t i o n in MnBi, and higher power l a s e r s .
C e r t a i n t e r n a r y i n t e r m e t a l l i c s such as MnA1Ge a r e
a l s o magnetooptically active and r e q u i r e lower power.
It is not yet c l e a r what m a t e r i a l offers the b e s t t r a d e off in p r o p e r t i e s .
LiA1 and LisSi (Battery E l e c t r o d e s )
Novel high e n e r g y - d e n s i t y b a t t e r y s y s t e m s have
been proposed for load leveling and vehicle a p p l i c a tions which r e q u i r e a l i t h i u m - b e a r i n g anode. The r e q u i r e m e n t s a r e : m.p, above that of the s a l t eutectic
e l e c t r o l y t e (~400~
high lithium content, low voltage
l o s s r e l a t i v e to lithium metal, and retention of capacity upon continued cycling. LiAI (Ref. 192) and Li~Si
(Refs. 193. 194) a p p e a r to have c o n s i d e r a b l e p r o m i s e
in this r e s p e c t . Not only do the3~ have a high lithium
content and adequate melting point but e l e c t r o d e
l o s s e s of l e s s than 0.3 V v i s - a - v i s lithium and capac i t i e s of over 2 A . h / g m have been m e a s u r e d .
Zr3A1 (Nuclear R e a c t o r S t r u c t u r a l M a t e r i a l )
M a t e r i a l s f o r fuel sheaths or p r e s s u r e tubes in this
application must be s t r o n g at p r o j e c t e d operating t e m p e r a t u r e s , c o r r o s i o n r e s i s t a n t to water or steam, and
have a low t h e r m a l neutron capture c r o s s - s e c t i o n . In
the past these r e q u i r e m e n t s have been met by alloys
b a s e d on an a - Z r solid solution m a t r i x . Recent work
by Schulson 195 and a s s o c i a t e s on Z r ~ A l - b a s e d c o m p o s i tions a p p e a r s to offer a new m a t e r i a l of g r e a t p r o m i s e .
The specific neutron capture c r o s s - s e c t i o n is low
(0.0096 cmZ/cm3). The c o r r o s i o n r e s i s t a n c e is comp a r a b l e to Z i r c a l o y 2, the p r e s e n t c o m m e r c i a l alloy
for this application and, as shown in Table II, Zr3AI
b a s e d compositions show a c o n s i d e r a b l e strength advantage over a Z r a l l o y s of e i t h e r p r e s e n t c o m m e r c i a l
or advanced development compositions while maintaining c o m p a r a b l e ductility. In addition the o r d e r e d
s t r u c t u r e should lead to low diffusion r a t e s and t h e r e fore to i m p r o v e m e n t s in c r e e p behavior and other diffusion p r o m o t e d p r o c e s s e s . Composition must be held
within n a r r o w l i m i t s ; above 9 pct A1 the DBTT r i s e s
to ~250~ and below 7 pet AI c o r r o s i o n r e s i s t a n c e can
be s e v e r e l y i m p a i r e d by the p r e s e n c e of an i n t e r c o n nected network of o~-Zr. Remaining p r o b l e m s a r e
that the m a t e r i a l shows notch s e n s i t i v i t y and some
growth and swelling upon i r r a d i a t i o n . ~96 However,
s u c c e s s has been achieved in p r e l i m i n a r y efforts to
f o r m p r e s s u r e tubes by extrusion, t97
NiTi (Shape M e m o r y Effect Alloy)
An e x t r a o r d i n a r y c l a s s of a l l o y s e x i s t s (mostly
b a s e d on i n t e r m e t a l l i c s ) that p o s s e s s the unusual
ability of r e m e m b e r i n g t h e i r past. 198 The nature of
this shape m e m o r y effect (SME) is shown s c h e m a t i cally in Fig. 36. Annealing a d e f o r m e d p a r t at high
t e m p e r a t u r e " f i x e s " the shape. The m a t e r i a l may be
differently d e f o r m e d at low t e m p e r a t u r e but upon
r e a n n e a l i n g at i n t e r m e d i a t e t e m p e r a t u r e the p a r t r e turns to its o r i g i n a l shape. Although the effect is exVOLUME 8A, SEPTEMBER 1977-1349
Anneal at
a high
temperature
NiTi
l e v e l s (see for e x a m p l e Fig. 38) c o m b i n e d with high
h y d r o g e n capacity. A f u r t h e r point of i n t e r e s t is that
the h y d r i d e s d e r i v e d f r o m LaCo5 a r e f e r r o m a g n e t i c
and exhibit a " m a g n e t o b a r i c " effect. 2~ That is the
e q u i l i b r i u m h y d r o g e n p r e s s u r e can be c o n t r o l l e d by
the applied m a g n e t i c field as shown in Fig. 39; i n -
Cool
Temperature
Phase
\
Shape
recovered
\\
Shape ~
partially
recovered
change \ \
tonew ~ \
structure \ 9
250O
/
4
/
Warm
/
--
/
/
2000
[ Phase
[ change
/ back to
Conductivity o,
(ohm.cm).1 1500
structure
1000
Deform by straightening
Time
Fig. 36-Schematic diagram of the shape memory effect (SME). Annealing at a high temperature "'fixes" the permanent shape. After being
deformed at a low temperature to some other shape, the alloy will
evert to its permanent shape upon being warmed. After Robinson.198
hibited by m a n y d i f f e r e n t b a s e a l l o y s , the c o m p o s i t i o n s
of g r e a t e s t c o m m e r c i a l i n t e r e s t a r e b a s e d on the compound N i T i . 199 This compound was f i r s t e x t e n s i v e l y inv e s t i g a t e d by B u e h l e r z~176
at the N a v a l O r d n a n c e L a b o r a t o r y who dubbed it " N i t i n o l " .
It has the C s C l - s t r u c t u r e at high t e m p e r a t u r e s but t r a n s f o r m s to a n o t h e r
s t r u c t u r e at low t e m p e r a t u r e ; it is this t r a n s f o r m a tion which is r e s p o n s i b l e for the SME. A m o n g the div e r s e a p p l i c a t i o n s u n d e r study o r a l r e a d y made of
this compound a r e w e l d l e s s c o n n e c t o r s for h y d r a u l i c
tubing, s e l f - d e p l o y a b l e space s t r u c t u r e s , pen d r i v e s
for s t r i p c h a r t r e c o r d e r s , f r e i g h t c a r " h o t b o x " d e t e c t o r s and b r a k e a c t u a t o r s , i m p l a n t a b l e blood clot
f i l t e r s , orthopedic and orthodontic d e v i c e s , and heat
e n g i n e s for u s i n g l o w - g r a d e heat s o u r c e s such as
s o l a r , g e o t h e r m a l , or p r o c e s s waste heat. Evidence
of the high l e v e l of i n t e r e s t in this c l a s s of compounds
is that they w e r e r e c e n t l y the s u b j e c t of an e n t i r e s y m posium.291
5O0
I
54
56
i
9
L
58
60
Atomic Percent Mg
62
Fig. 37-Electrical conductivity of hquid Bi-Mgalloys near the stoichiometric composition MgsB]2demonstrating the existence of a liqmd
semiconductor. Open circles, data of Ilschner and Wagner:closed circle
data of Colhngset al After Colllngset al 202
50
40
30
20
LaNi5 I I I,'1
81~
66~
PH 2
(atm)
10
f
52~
5
21~
2 ,r
lr
7
0
I
I
I
I
I
I
1
2
3
4
5
6
Hydrogen Concentration (at. Hlmol LaNis)
Fig. 38-Hydrogen desorption isotherms of LaNis at various temperatures. After van Vucht et al. 2o3
LaCosHx
Mg3Bi2 (Liquid S e m i c o n d u c t o r )
A v e r y few s u b s t a n c e s exhibit the u n u s u a l p h e n o m e non of s e m i c o n d u c t i n g b e h a v i o r in the liquid state as
shown for MgsBiz in Fig. 37.
0
T = 22oC
H;ppl
=
1 lkOe
p = 2.4 atm
LaNi5 (Hydrogen A b s o r b e r )
I n v e s t i g a t o r s at the P h i l i p s R e s e a r c h L a b o r a t o r i e s 2~
in the N e t h e r l a n d s d i s c o v e r e d about 1970 that the
a b s o r p t i v e capacity of LaNis(CaCu5 s t r u c t u r e ) r e a c h e d
the p h e n o m e n a l l e v e l of about 6 a t o m s of hydrogen
p e r f o r m u l a unit of the i n t e r m e t a l l i c , i . e . about 6.2
• 1022 a t o m s / c c or about twice the hydrogen d e n s i t y
of liquid hydrogen! (Several other i n t e r m e t a l l i c s i n cluding FeTi,~~
z~ and ErCo3 (Ref. 206) show s i m i l a r but l e s s m a r k e d a b s o r p t i v i t y ) . C e r t a i n e l e m e n t a l
m e t a l s , e . g . U andHo, p o s s e s s c o m p a r a b l e or g r e a t e r
hydrogen capacity but they lack the f e a t u r e that r e n d e r s
the i n t e r m e t a l l i c compounds of i n t e r e s t , n a m e l y v e r y
f a s t uptake and r e l e a s e r a t e s at m o d e s t p r e s s u r e
1350-VOLUME 8A, SEPTEMBER 1977
Z~p --- 0.02 atm
)
I
I
I
80
40
0
=
t (see)
Fig 39-Demonstration in LaCosHx of the magnetobaric effect, i e,
alteration of the equfllbrmm hydrogen pressure by application of a
magnetic field. Here is shown the pressure change resulting from
switching on and off a magnetic field of 11 tesla (1 1 KOe). After
Kuijpers 2o7
METALLURGICALTRANSACTIONSA
c r e a s i n g the a p p l i e d f i e l d i n c r e a s e s the m a g n i t u d e of
the effect.
T h e s e unusual p r o p e r t i e s have s u g g e s t e d a n u m b e r
of p o t e n t i a l a p p l i c a t i o n s .208 F o r e x a m p l e they might
be u s e d a s a c o m p a c t s t o r a g e s o u r c e f o r h y d r o g e n
which could o p e r a t e at a constant, m o d e r a t e p r e s s u r e
i n s t e a d of a high p r e s s u r e (but d e c r e a s i n g with t i m e )
a s with c o n v e n t i o n a l s t e e l t a n k s t o r a g e of g a s e o u s
h y d r o g e n . T h e r m a l a b s o r p t i o n c o m p r e s s o r s have a l s o
been e n v i s i o n e d 2~ which would be c h a r g e d with h y d r o gen a t r o o m t e m p e r a t u r e and would s u p p l y c o m p r e s s e d
gas when h e a t e d to a h i g h e r t e m p e r a t u r e . If the c o m p r e s s o r w e r e coupled to a t u r b i n e o p e r a t i n g at an even
h i g h e r t e m p e r a t u r e , e x p a n s i o n of the gas in a c l o s e d
B r a y t o n c y c l e could c o n v e r t about 90 p c t of the high
t e m p e r a t u r e h e a t input to e l e c t r i c i t y while u s i n g about
3 kw of low t e m p e r a t u r e heat ( c o m p r e s s o r d e s o r p t i o n )
p e r kw of e l e c t r i c i t y . T h e s e i n t e r m e t a l l i c h y d r i d e s
have a l s o b e e n c o n s i d e r e d a s a c r y o s t a t w h e r e t h e i r
a b s o r p t i o n of e v a p o r a t i n g h y d r o g e n f r o m a liquid hyd r o g e n bath could be u t i l i z e d to m a i n t a i n a c o n s t a n t
temperature.
Pbl-xSnxTe (Air Pollution Monitor)
L e a d tin t e l l u r i d e i s a s e m i c o n d u c t i n g compound
which can be c a u s e d to e m i t i n f r a r e d l a s e r r a d i a t i o n .
A d j u s t m e n t of the c o m p o s i t i o n " t u n e s " the l a s e r to
e m i t at w a v e l e n g t h s f r o m 6.5 to 32 pan, thus m a t c h i n g
the s t r o n g i n f r a r e d a b s o r p t i o n l i n e s of the m o s t c o m mon a i r p o l l u t a n t g a s e s . O p e r a t i n g at 77 K, s u c h d e t e c t o r s p e r m i t m e a s u r e m e n t of c o n c e n t r a t i o n s in the
ppb r a n g e with v e r y high s p e c i f i c i t y f o r the pollutant
species.21~ An SEM p h o t o g r a p h of w h i s k e r s o b t a i n e d
d u r i n g s o m e c r y s t a l growth s t u d i e s T M on this c o m pound i s shown in F i g . 40.
R E F e 2 (Giant M a g n e t o s t r i c t o r s )
L a v e s p h a s e compounds of i r o n with the r a r e e a r t h
e l e m e n t s c o m b i n e a huge m a g n e t o s t r i c t i o n with a l a r g e
m a g n e t i c a n i s o t r o p y and a high m a g n e t i c s a t u r a t i o n .
Not only can the m a g n e t o s t r i c t i o n c o e f f i c i e n t s , Xs
= 2/3 (Xll - X• b e e x t r e m e l y l a r g e (>1700 • 10-6 f o r
TbFe2 v s <100 • 10-6 f o r the e l e m e n t a l f e r r o m a g n e t s )
but they a r e r e a l i z e d at r o o m t e m p e r a t u r e . T h e s e
p r o p e r t i e s m a k e the compounds c i t e d a t t r a c t i v e f o r
high p o w e r t r a n s d u c e r s , p e r m a n e n t m a g n e t s , a c o u s t i c
d e l a y l i n e s and v a r i o u s t y p e s of m i c r o p o s i t i o n i n g d e v i c e s . C l a r k 212 and T a y l o r 2~3 have r e c e n t l y p u b l i s h e d
reviews.
Thus f a r we have s p o k e n of the p r a c t i c a l i m p o r t of
i n t e r m e t a l l i c s only in the p o s i t i v e s e n s e , i . e . w h e r e
f u n d a m e n t a l knowledge of t h e i r s y n t h e s i s , p r o p e r t i e s
and p r o c e s s c o n t r o l has l e d to a c t u a l o r p r o j e c t e d a p p l i c a t i o n s of the compounds t h e m s e l v e s . In f a c t t h e r e
i s a n o t h e r s i d e to the s t o r y - c a s e s w h e r e the s c i e n t i f i c
u n d e r s t a n d i n g of the o c c u r r e n c e and f o r m a t i o n k i n e t i c s
of i n t e r m e t a l l i c compounds has f a c i l i t a t e d m a t e r i a l s
s e l e c t i o n and p r o c e s s c o n t r o l by e n g i n e e r s s o a s to
prevent or minimize intermetallic formation where
t h i s would be d e l e t e r i o u s to the p e r f o r m a n c e of the
a l l o y . A few e x a m p l e s of t h i s c l a s s w i l l be given.
AuA12 ( F o r m e d in Thin F i l m I n t e g r a t e d
Circuit Conductors)
Both gold and a l u m i n u m a r e u s e d a s c o n d u c t o r s in
IC d e v i c e s b e c a u s e of t h e i r e x c e l l e n t conductivity,
s t a b i l i t y and e a s e of d e p o s i t i o n . S o m e t i m e s both a r e
u s e d in c o n t a c t i n g p a r t s in the s a m e d e v i c e and the
e l e c t r o n i c s i n d u s t r y then found i t s e l f c o n f r o n t e d with
the " p u r p l e p l a g u e " , a c a t a s t r o p h i c e m b r i t t l e m e n t a t
the c o n t a c t i n t e r f a c e b e t w e e n the two m e t a l s . (See
F i g . 41) AuA12, whose s t r i k i n g p u r p l e c o l o r had b e e n
noted by R o b e r t s - A u s t e n 214 a s e a r l y a s 1891, had
f o r m e d at the r e l a t i v e l y low t e m p e r a t u r e s g e n e r a t e d
by J o u l e h e a t i n g of the junction. The K i r k e n d a l l v o i d s
f o r m e d by the diffusion p r o c e s s t o g e t h e r with the high
thermal expansion stress induced between adjacent
i n t e r m e t a l l i c p h a s e s l e d to a b r i t t l e joint. With p r o p e r
d e s i g n of the c o n t a c t s and c a r e in the diffusion bonding p r o c e s s t h e s e d i f f i c u l t i e s have been m i n i m i z e d . 215
S i g m a P h a s e ( E m b r i t t l e r of High
Temperature Alloys)
In m a n y a l l o y s t e e l s and high t e m p e r a t u r e a l l o y s ,
the a p p e a r a n c e of a c o m p l e x o r d e r e d p h a s e known a s
s i g m a * h a s b e e n c o r r e l a t e d with d r a s t i c r e d u c t i o n s
in s t r e s s - r u p t u r e life and r u p t u r e d u c t i l i t y . S i g m a
f o r m s v e r y s l u g g i s h l y with long t i m e high t e m p e r a t u r e e x p o s u r e . It i s h a r d and b r i t t l e i t s e l f , and i t s
e f f e c t s a r e e x a c e r b a t e d by i t s m i c r o s t r u c t u r a l c h a r a c t e r i s t i c s : thin, s h a r p p l a t e l e t s l o c a t e d p r e f e r e n t i a l l y
Fig. 40-SEM of single crystals of PbxSn 1 xTe grown for studies of
their ir laser action. Courtesy of Cambridge Instruments.
METALLURGICAL TRANSACTIONS A
*The prototypecompoundis FeCrm the Fe-Crbinarysystem,but the composmon of o vanes wdely and it need not cont~n either Fe or Cr.
VOLUME 8A, SEPTEMBER 1977-1351
10000
8000
Initial
6000
Permeability,
Fi
4000
Ni3Fe~ 1
Quenched-.~,~
2000
0
20
40
60
80
100
Percent Nickel
Fig. 42-Initial permeabdity as a function of composltmn m the Fe-Ni
system for heat treatments presumed to yield the disordered structure
(quenched) and the ordered structure (tempered). After Elmen.
at g r a i n b o u n d a r i e s ~ Sigma can be e l i m i n a t e d by
c o m p o s i t i o n a l control, but in alloys of s e v e n or m o r e
c o m p o n e n t s this was tedious and h a p h a z a r d at best.
Boesch and Slaney 216 i n t r o d u c e d a c o m p u t a t i o n a l t e c h nique, l a t e r i m p r o v e d by Woodyatt e t al. z17 B a r r o w s
and Newkirk, 2'8 and W a l l a c e 219 that d e r i v e s an a v e r a g e
e l e c t r o n v a c a n c y n u m b e r f r o m an e s t i m a t e of the
r e s i d u a l m a t r i x c o m p o s i t i o n of the alloy after allowing for the i n i t i a l p r e c i p i t a t i o n of d e s i r e d p h a s e s .
S i g m a - p r o n e alloys a r e those which exceed a c e r t a i n
c r i t i c a l e l e c t r o n v a c a n c y n u m b e r . A q u a n t i t a t i v e guide
to the a p p r o p r i a t e c o m p o s i t i o n a l m o d i f i c a t i o n of even
quite complex, m u l t i c o m p o n e n t alloys is thus at hand.
P e r m a l l o y Ni3Fe (High Magnetic
P e r m e a b i l i t y Alloy)
High p e r m e a b i l i t y in this b i n a r y a l l o y is o b t a i n e d
w h e r e m a g n e t o s t r i c t i o n and m a g n e t o c r y s t a l l i n e a n i s o t ropy a r e m i n i m i z e d at the Ni3Fe c o m p o s i t i o n , Howe v e r , this useful condition is only a c h i e v e d when the
alloy is in the d i s o r d e r e d condition obtained by q u e n c h ing f r o m high t e m p e r a t u r e s . Slow cooling o r r e h e a t t r e a t i n g at lower t e m p e r a t u r e s begins to f o r m the
o r d e r e d p h a s e with a s h a r p r e d u c t i o n in p e r m e a b i l i t y
as shown i n F i g . 42 and such t r e a t m e n t s m u s t t h e r e f o r e be avoided.
p a r a m e t e r s of the c o n s t i t u e n t a t o m s .
b) S u c c e s s f u l a p p l i c a t i o n s of i n t e r m e t a l l i c s do not
r e s u l t f r o m the m e r e knowledge of t h e i r c o m p o s i t i o n ,
c r y s t a l s t r u c t u r e , and i n t r i n s i c p r o p e r t i e s but r e q u i r e
as well a s k i l l f u l and u n d e r s t a n d i n g c o n t r o l of t h e i r
processing.
c) T h e r e is d e s i r a b l y and n e c e s s a r i l y a s t r o n g i n t e r p l a y b e t w e e n s c i e n c e and technology in the developm e n t of the i n t e r m e t a l l i c field. The t e c h n o l o g i c a l
opportunity f o r e c a s t by s o m e unique p r o p e r t y m e a s urements stimulates further related scientific investigation. C o n v e r s e l y s c i e n t i f i c a d v a n c e s , both those
s p e c i f i c to i n t e r m e t a l l i c s and those p e r t i n e n t to m e t a l l u r g y m o r e g e n e r a l l y , f a c i l i t a t e the r a t e of r e d u c tion to p r a c t i c e of e m p i r i c a l d i s c o v e r i e s .
What now of the f u t u r e - c a n any t r e n d s be d i s c e r n e d ?
T h e f i r s t that I s e e is a g r e a t e r a p p r e c i a t i o n and cont r o l of s u b g r a i n s t r u c t u r e : o r d e r d o m a i n s , p r e c i p i t a tion s t r u c t u r e , c o m p o s i t i o n a l modulation by spinodal
d e c o m p o s i t i o n , d i s l o c a t i o n a r r a y s and point defect
s t r u c t u r e s , e x a m p l e s of which a r e i l l u s t r a t e d in F i g s .
43 to 47. We have come to r e a l i z e that m o s t p r o p e r ties of i n t e r e s t depend upon quite e x q u i s i t e d e t a i l s of
s t r u c t u r e , no one of which is d e t e r m i n a t i v e by itself,
but r a t h e r the whole e n s e m b l e with its d e l i c a t e b a l a n c e s of bonding f o r c e s and t h e i r a l t e r a b i l i t y by t e m p e r a t u r e , m i n o r v a r i a t i o n s in c h e m i s t r y or m e c h a n i cal, e l e c t r i c a l or m a g n e t i c s t r e s s . It is, of c o u r s e ,
one thing to r e a l i z e a c o r r e c t p r i n c i p l e and quite
a n o t h e r to be able to s u b j e c t m a t e r i a l s to the r e q u i s i t e
d e g r e e of c o n t r o l . F o r example, s e v e r a l d i f f i c u l t i e s
a r e p e r c e i v e d in a c h i e v i n g the type of s t r u c t u r e cont r o l j u s t cited: ppm q u a n t i t i e s of i m p u r i t y can w r e a k
l a r g e effects in m a n y bulk p r o p e r t i e s ; s u b m i c r o s c o p i c
defects i n t r o d u c e d by p r i o r p r o c e s s i n g h i s t o r y can be
s i m i l a r l y potent; and, of a l l defects p r e s e n t and detectable, only s o m e unknown f r a c t i o n a c t i v e l y affect
the p h e n o m e n o n in question, the o t h e r s having b e e n
i n a c t i v a t e d by i n t e r a c t i o n with i m p u r i t i e s o r o t h e r d e fects.
R E T R O S P E C T I V E ANALYSIS AND
SPECULATIONS FOR THE F U T U R E
In r e v i e w i n g this s u b j e c t , I have t r i e d to s e r v e two
b r o a d goals: f i r s t to call a t t e n t i o n to i n t e r m e t a l l i c
compounds as a b r o a d c l a s s of m a t e r i a l s of g r e a t
p r a c t i c a l i m p o r t and as a f a s c i n a t i n g topic of s c i e n tific inquiry; s e c o n d l y by e x p l o r i n g s o m e of the r e l e vant m e t a l l u r g i c a l h i s t o r y to r e v e a l s o m e t h i n g of the
p r o c e s s by which both ideas and p r a c t i c a l d e v e l o p m e n t s evolve and to e m p h a s i z e how v e r y far b a c k in
t i m e s o m e of the t h r e a d s m a y be t r a c e d .
When we c o n t r a s t o u r p r e s e n t view of the s u b j e c t
with that of our p r e d e c e s s o r s of a c e n t u r y or m o r e
ago, one is s t r u c k a g a i n by the v e r i t y of the F r e n c h
saying, " p l u s ca change, plus c ' e s t la m e m e c h o s e " .
In this s e n s e , t h r e e g e n e r a l i z a t i o n s s e e m s t i l l to hold:
a) The i n t r i n s i c p r o p e r t i e s of i n t e r m e t a l l i c c o m pounds a r e t r u l y unique and at p r e s e n t l e v e l s of u n d e r s t a n d i n g a r e not p r e d i c t a b l e f r o m the f u n d a m e n t a l
1352-VOLUME 8A, SEPTEMBER 1977
Fig. 43-Magnetic domains m C u l 7 S m ~ revealed by the Kerr magnetooptm effect. Rosette structures in certain of the grains result from
magnetostat]c energy reduction of domain walls in the surface region
for those grams with the easy-axzs normal to the surface, magnification
348 times. After Becker.2z2
METALLURGICALTRANSACTIONS A
, I
V
(
i~ "Jli
a]
Fig. 44 Ordered domains in CuAu with c-axes of the tetratragonal
structures variously oriented in the three (001) directmns. W~thin these
domains other domains can exist with layers that are out-of-step with
their neighbors. Domain structure revealed by electron microscopy of
chromium shadowed carbon replica of chemically etched surface.
After Syutkina and Yakovleva.TM
Fig. 45-Replication micrograph of Nia(Ti,A1) precipitates in an experimental high temperature alloy. Large cubes developed during isothermal
anneal, fine cubes curing cooling from the annealing temperature.
Cubic morphology and quasiregular array arise from the close crystallographic and dimensional relatmnships of precxpitate and host,
magmfication 10,000 times. From unpublished research by Westbrook.
METALLURGICAL TRANSACTIONS A
Fig. 46-(111) dark field transmission electron micrograph of the
quenched alloy Cu2.sMno.sA1 aged at 300~ for 30 s. During aging a
spinodal decomposition of the CsC1single phase structure takes place
to produce a compositionally modulated structure of CuaAl-rich and
Cu2MnAl-rich regions. This is the tweed-hke background structure.
Under the particular diffraction conditions the smoothly curved antiphase domain boundaries of the as-quenched alloy are imaged as well
as the compositional modulations. Magnification 80,000 times. After
Bouchard and Thomas. 224
A n o t h e r p r o s p e c t b e f o r e us is e n h a n c e d a t t e n t i o n to
be paid to compounds of m e t a s t a b l e s t r u c t u r e which
a r e not r e a l i z a b l e by o r d i n a r y m e t h o d s of m e l t i n g and
c a s t i n g but n e e d be p r e p a r e d by s p e c i a l m e t h o d s . R e f e r e n c e is m a d e h e r e to high p r e s s u r e s y n t h e s i s , 22z 228
e l e c t r o d e p o s i t i o n , e29'2s~ v a p o r p h a s e d e p o s i t i o n T M and
u l t r a r a p i d quenching. 23~-~34. By such m e a n s , t h e r e may
be f o r m e d : n o n e q u i l i b r i u m p h a s e s of n o r m a l c r y s t a l
s t r u c t u r e s (at both n o r m a l and a b n o r m a l c o m p o s i tions), n o v e l s t r u c t u r e s , and a m o r p h o u s m a t e r i a l s .
Not only is t h e r e the p o t e n t i a l for finding m a t e r i a l s
with new c o m b i n a t i o n s of p r o p e r t i e s , but the a c q u i s i tion of data on m e t a s t a b l e p h a s e s w i l l undoubtedly
c o n t r i b u t e to our u n d e r s t a n d i n g of the c r y s t a l c h e m i s t r y of i n t e r m e t a l l i c s g e n e r a l l y .
Next, the p o s s i b i l i t i e s i m p l i c i t in d e a l i n g with c o m pounds whose g r o s s c h e m i s t r y is m u c h m o r e c o m p l e x
than those in use today can be f o r e s e e n . M o s t of the
e x p l o i t e d compounds have been b i n a r y in c h a r a c t e r ;
only in a few i n s t a n c e s , as with d e n t a l a m a l g a m o r the
t e r n a r y s i l i c i d e T r i b a l o y s , have h i g h e r o r d e r c o m p l e x e s b e e n applied. Many t e r n a r y i n t e r m e t a l l i c s a r e
known 23s whose p r o p e r t i e s have b e e n l i t t l e studied, but
the p o s s i b i l i t i e s a r e e v e n m o r e manifold. On the one
hand we have the p o s s i b i l i t y of s u b s t a n t i a l solid s o l u tion f o r m a t i o n within the s t r u c t u r a l m o t i f of a given
b i n a r y b a s e compound. As an e x t r e m e e x a m p l e of this
s o r t , P a r t h ~ 236 r e c e n t l y a c h i e v e d s y n t h e s i s of a s e v e n e l e m e n t compound, (Cux~.sZn23GaT.sGes)(As~6Se3oBr4), by
f o l l o w i n g v a l e n c e e l e c t r o n c o n c e n t r a t i o n r u l e s f o r the
t e t r a h e d r a l zinc blende s t r u c t u r e . S i m i l a r l y a q u a t e r n a r y L a v e s p h a s e MgsCu2Ni2Zn2 is known with the
MgCu2 s t r u c t u r e . 232 On the o t h e r hand, q u a t e r n a r y and
h i g h e r o r d e r compounds a r e known which e i t h e r p o s s e s s unique s t r u c t u r e s or a r e s u p e r s t r u c t u r e s d e r i v e d
f r o m known b i n u r y o r t e r n a r y s t r u c t u r e s . As e x a m *The referencescited are only exemplaryof the work that has been done
along these lines. The literature is sufficmntlyextensivethat separate rewew
articles could be written on each of these topics
VOLUME 8A, SEPTEMBER 1977-1353
Fig. 47-Bright field transmission
electron mlcrograph of paired
superlattice d~slocationsin Fe3Si
after 2,2 pct strata at 298 K
showing both screw (b) and edge
(a) dislocation locks, as well as
annihilation of screw segments
(c) Normal to the foil IS(1 I0).
From Lakso and
Marcinkowski.Z2s
ples t h e r e m a y be cited A18FeMgeSiG d e r i v e d f r o m the
Fe2P s t r u c t u r e 23s and Ag2In~SnSb3Te3 d e r i v e d f r o m the
zinc blende s t r u c t u r e , z39 It s e e m s c e r t a i n that the lead
toward the d i s c o v e r y of new i n s t a n c e s of such c o m p o s i t i o n a l l y c o m p l e x s t r u c t u r e s will n e c e s s a r i l y be
t a k e n by t h e o r e t i c a l r a t h e r than e x p e r i m e n t a l app r o a c h e s . The m o t i v a t i o n for such s e a r c h e s will, of
c o u r s e , d e r i v e f r o m the knowledge that d e s i r e d p h y s i cal p r o p e r t i e s of a c r y s t a l s t r u c t u r e a r e a s s o c i a t e d
with c e r t a i n c o o r d i n a t i o n s of a t o m s and t h e i r s e p a r a tions f r o m each other and that complex compounds a r e
l e s s s u s c e p t i b l e than s i m p l e b i n a r i e s to diffusion controlled degradation processes.
I n c r e a s i n g a t t e n t i o n will d o u b t l e s s be paid to the
exploitation of i n t e r m e t a l l i c compounds in composite
s t r u c t u r e s , whether f o r m e d n a t u r a l l y as by e u t e c t i c or
eutectoid t r a n s f o r m a t i o n o r a r t i f i c i a l l y by m e c h a n i c a l
m e a n s . Although the o u t s t a n d i n g m e c h a n i c a l p r o p e r t i e s of i n t e r m e t a l l i c s c o m m e n d them for i n c l u s i o n in
c o m p o s i t e s d i r e c t e d at m e c h a n i c a l a p p l i c a t i o n s , they
a r e also a t t r a c t i v e for other types of a p p l i c a t i o n . 24~
As e x a m p l e s t h e r e m a y be cited: the u n i d i r e c t i o n a l l y
s o l i d i f i e d e u t e c t i c of A1-A13Ni with v i r t u a l l y the s a m e
conductivity as p u r e a l u m i n u m but with five t i m e s the
u l t i m a t e t e n s i l e strength; ~41 the a l i g n e d InSb-NiSb eutectic whose a n i s o t r o p i c m a g n e t o r e s i s t a n c e (InSb is a
s e m i c o n d u c t o r , NiSb is a m e t a l l i c conductor) is
u t i l i z e d as a field plate in an e l e c t r i c locomotive
b r a k e control; 242 and compounds s u c h as PdsU (Ref.
243) and (La, Ce)A12 (Ref. 244) exhibiting giant t h e r m o e l e c t r i c power and, hence, of i n t e r e s t as t e m p e r a t u r e s e n s o r s and e n e r g y c o n v e r t e r s .
F i n a l l y a s we have s e e n with p h a s e d i a g r a m s and
c r y s t a l s t r u c t u r e s , it has b e e n n e c e s s a r y in the past
to collect and s y s t e m a t i c a l l y c o m p i l e e m p i r i c a l data
to a c e r t a i n point in o r d e r to p e r m i t s o m e i m a g i n a t i v e
i n d i v i d u a l to p e r c e i v e a p a t t e r n which then p e r m i t s a
m o r e f u n d a m e n t a l g e n e r a l i z a t i o n . We may, t h e r e f o r e ,
s p e c u l a t e w h e t h e r the c u r r e n t l y b u i l d i n g data on
NMR 245 and e l e c t r o n i c d e n s i t y of s t a t e s 246,z47 will play
a s i m i l a r r o l e in the f u t u r e m e t a l l u r g y of i n t e r m e t a l lics.
1354 VOLUME8A, SEPTEMBER 1977
i,i
\-
?
V
m~
~Ow
_
~
9
v
Fig. 48-Field ion micrograph of CoPt ordered for 71 h at 800~ The
(001) superlattice plane is shown and contrast corresponding to both
single misplaced Pt atoms (additional image points between rings) and
"bound wrong pairs" (vacant site contrast in the Pt rings) can be seen.
After Southworth. 226
In c l o s i n g this r e v i e w , I can think of no m o r e fitting
way to s u m m a r i z e nay own f e e l i n g s toward the s u b j e c t
than to quote the f i n a l r e m a r k s f r o m H a t c h e t t ' s p a p e r 87
of 1803 :
"Much, however, r e m a i n s to be done, and much m a y
be expected, f r o m a r e g u l a r and s y s t e m a t i c a l s e r i e s
of e x p e r i m e n t s on the p r o p e r t i e s of compound m e t a l s . F o r , e x c l u s i v e l y of the i m m e d i a t e a p p l i c a t i o n
of m a n y of the alloys to e c o n o m i c a l p u r p o s e s , it
cannot be doubted that s c i e n c e will d e r i v e other
c o n s i d e r a b l e advantages; o u r ideas c o n c e r n i n g the
p r o p e r t i e s of the m e t a l s , w h e t h e r s i m p l e o r mixed,
will be much e n l a r g e d , and clouds of e r r o r s , with
the t r a d i t i o n a r y p r e j u d i c e s which as yet shade this
b r a n c h of h u m a n knowledge, will be d i s p e r s e d . "
METALLURGICALTRANSACTIONSA
APPENDIX
WEIGH,
t
s.
Ag-Hg-Sn. ~
PER C E N T T I N
Cu Sn
~" '~
"
"
.50/ ,," i l~.~o ~176
.00108,~
7.,"
/
ltY''~
GO0
Xi +~l+ L
19t (30 6)
5)
l
43 1158.61
i
Ag "
~/
8 +Llq.
~
~
"
v
--
.
PER CENT MERCURY
.
.
.
~
Bi
~" Ng
)" +Liq"
~oo
400
/
I
4~* 5 (59 Ol
~=~
~ - , 86"r (82 4)
Cobalt
\
1600
1500
30O
200
17(I 3)
,oo
189o
10
20
30
Cu
448(Go31/l
186o
Y
40
50
60
ATOMIC PER CENT TIE
70
1400
1300
1200
1987(993
80
10
90
100
Sn
Temperature,
1100
~
1000
900
800
700
Content,
o,
wt. % ,
, o.o .o,
, o.o ,
,
.oo,
.
Z40
,~,./
sgS
600
500
4O0
20
I
45C
WEIGHT PER CENT TIN
30
40
50
I
a
1
60
I
70
i
80
I
10
20
E
E
40
50
60
70
Cobalt Content, at. %
80
90
100
90
I
Hg-Sn
40C
30
E
Nb-Sn
}5C
300
~ooo
Z50
~*ZO0
Nb3Sn + L I Q U I D
==
t.
I$o0
150
tOO
90~
IOoo--
9 3 0 =* 8~
~gs;
0
.oo_
1
P
,
'
-389r
-50
,i
-IOO
Hg
,;
io
3'o
;o
so
GO
ATOMIC PER CENT TIN
METALLURGICAL TRANSACTIONS A
,o
;o
I
90
,o0
Sn
IOO~o Nb i0
20
,,,.3s0. N~,Sns I
~0
40
~'QU~D
84s-* 7~
....... f ....
.oo
NbSn2+$n231
9~
Nb6Sn5* NbSn2
NbSn2* LIQUIO
SO
60
Q/~ TI N
--
70
80
90
iOO~
Sn
V O L U M E 8A, S E P T E M B E R 1 9 7 7 - 1 3 5 5
Co-Mn-Ri
A
,o
:o .o
,o
i
,,oo,
110041063~
Cu 1 Sb
'
'
//,
\\
/i
l!i\
~
too
~ossi ~
Co
no
so Moco3
ao Mosco~ ~,o
600
~
46(621
500
~"t-~488
~ L
400 j
\, Cv:_3~_5_o_j
[[
zo
63(7651
~I
300!/
I
g
lO0i
oi
o
C.
,~
zo
3o
,~o
;o
~o
ATOMIC PER CENT ANTIMONY
;o
;o
;o
,oo
Sb
ACKNOWLEDGMENTS
WEIGHT
I0I
1100
'1000
900
800
PER
20
I
CENT
30
I
aRSENIC
40
1
So great a number of friends and c o l l e a g u e s have
contributed to this paper that it is not f e a s i b l e to cite
each individually. My debt to those unmentioned is
none the l e s s and m y gratitude is great. T h o s e who
have provided i l l u s t r a t i o n s and data have been cited in
the text. Thanks a r e due D r s . Cyril Smith, M. Fine,
W. L e s l i e , J. Burke, and J. W e r n i c k who c r i t i c a l l y r e v i e w e d an e a r l y draft of the m a n u s c r i p t and offered
many insightful c o m m e n t s . R e f e r e n c e librarians, Ms.
V. Chase and Ms. W. Crain, displayed much ingenuity
and good humor in t r a c k i n g down many an o b s c u r e
r e f e r e n c e . Finally, Ms. L. Phan produced n u m e r o u s
typed drafts with great s k i l l and incredible patience.
~_50
As-Cu
0,30
8309o~m I
,S
700
6.85(80118.4
6~ ~
(21)
600
REFERENCES
~5\2 (39)
Cu)
500
400
6.7
(7.81
-380 ~
4
I
I
300
200
.5.9 (6 91
Cu
1356
505*
1
1o
20
ATOMIC
PER CENT
30
VOLUME 8A, SEPTEMBER 1977
,/o
ARSENIC
50
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