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Diffusion of Cu in AuCu alloy
Scripta
METALLURGICA
Vol. 4, pp. 605-610, 1970 Printed in the U n i t e d States
Pergamon
Press,
Inc.
DIFFUSION O F Cu in AuCu A L L O Y M. Khobaih ~ and K . P . G u p t a D e p a r t m e n t of M e t a l l u r g i c a l E n g i n e e r i n g Indian i n s t i t u t e of T e c h n o l o g y , K a n p u r , India ___..-_
(Received
June
19,
1970)
W h e n a powder compact containing two metalpowders
is heated at a given temperature for
sufficiently long time it is expected to produce a h o m o g e n e o u s alloyof appropriate composition. While this appears to be true for isomorphous
binary systems (I) the s a m e does not s e e m to
occur for binary systems involving inter~nediate phases (2, 3) or order disorder transformation (4).
Jordan and D u w e z (4) observed a pseudoequilibrium
phase in sintered powder
compacts
containing 7 5 % C u
between
C u and A u C u ordered
and Z 5 % Au, whereas the s a m e powder
compacts readily produced homogeneous A u C u 3 alloy at temperatures above 450°C.
The pseu-
doequilibrium in C u - A u compacts has beenattrtbuted tothe relative stability of the intermediate ordered phase.
One would then expect to find appreciable difference in the diffusivity of C u i n
the ordered and the disordered A u C u
phases.
In the present
investigation diffusion of C u in
A u C u alloy has been studied. A u C u alloy was prepared by melting 99.999% pure A u and C u in an argon gas atmosphere induction melting unit.
The alloy was remelted
prepare a I/2" dia. rod specimen,
in an evacuated and sealed quartz capsule to
slowly cooled down to 800°C and homogenized at this tem-
perature for 5 hours and finally quenched in cold tap water to retain the disordered structure. This treatment was necessary before cold swaging it into thinner rod. T w o diameter x 5 c m long were prepared
specimens of 5 m m
by turning the swaged alloy on a precision lathe and the
specimens were annealed in evacuated and sealed quartz capsules,
one at 800°C for two days
and the other at 330°C for 7 days, and finally quenched incold tapwater so as to produce the dis-
P r e s e n t a d d r e s s : D e p a r t m e n t of M e t a l l u r g y , U n i v e r s i t y of C o n n e c t i c u t , S t o r r s , Connecticut, U . S . A . 605
ordered and the ordered structures in a bath containing
175 gm/lit
Both specimens
respectively.
CuSO4.5
at bath operating conditions of 4 volts,
H20,
100 gm/lit
15 amp/sq.ft
rature and slow stirring with a magnetic stirrer. coherent,
adherent
and uniform all over.
each
of the
specimens
300°,
325O,
350°,
550°,
625’
and 9 days at 625’
sufficiently wide diffusion
were electroplated
H2SO4 and 20 to 30 gm/lit
current density,
25’ to 30°C
with Cu
Agar and
bath tempe-
The deposited copper was very fine grained,
Three
specimens of 13 mm length were cut from
and 7OO’C.
60 days at 300°C,
and 700°C, zones.
The temperature
especially
The annealed
at the lower temperatures specimens
turned from the specimen for chemical analysis. of Cu by calorimetric
lable for each depth of cut,
control was better than+
45 days at 325’ and 350°C,
were
depth of 1 mm for the ordered state and 2 mm for the disordered
with the analysis
4, No.8
and diffusion annealed in evacuated and sealed quarts capsules
Long diffusion times were allowed, 550°C
Vol.
DIFFUSION OF Cu IN AuCu ALLOY
606
1°C.
20 days at
as to produce
faced off from one end toa
state before
Since the presence
methodand onlya few milligrams
the calorimetric
so
at
thin layers were
of Au does not interfere of turnings were avai-
analysis was found most suitable and accurate for
the present investigation.
All chemical analysis of Cu were done by a Bausch 81 Lomb Spectro-
nit 20 spectrocolorimeter
using a 2% aqueous solution of ethylene diamine as the coloring agent
which has been claimed three times
more
sensitive
FIG.
than the usually used reagent
1
Concentration Profile of Cu in a Cu/AuCu Diffusion Couple at Annealing Temperature 350°C and Annealing Time 1080 hours.
NH4OH. (5).
Vol.
4, No.
8
DIFFUSION
OF Cu IN A u C u ALLOY
607
A typical copper concentration profile obtained in t~e present investigation is shown in Fig.
I.
The diffusion coefficient calculations
were done by the standard B o l t z m a n n - M a t a n o
method and the diffusion data for the six specimens plotted as logl0D against I/T,
Fig. 2, gave the values of D o and Q for the two states of A u C u TABLE
Diffusion Data for C u / A u C u State of AuCu alloy
Disordered
Ordered
are shown in Table I. The results w h e n
Temperature i n OK
1
Couple at Various Temperatures
Diffusivity, D in cmZ/sec
973
1.94 x 10 -9
898
1.01 x I0 "9
823
5.35
623
1 . 2 0 x 10 -11
598
8.75 x 10 -12
573
5.83 x I0 "12
x
DO in cmZ/sec
Activation Energy, Q in K. C a l / g m . a t o m
Z.36 x 10 -6
13.63
7.94 x 10 -8
10.72
10 - 1 0
iI FIG. 2 LoglOD a s a F u n c t i o n of I / T f o r the O r d e r e d and D i s o r d e r e d States of A u C u . alloy.
I t a p p e a r s f r o m the
results
a c t i v a t i o n e n e r g y for d i f f u s i o n of C u .
t h a t the
two s t a t e s of A u C u a l l o y h a v e a l m o s t the s a m e
T h i s p r o b a b l y i s n o t s u r p r i s i n g b e c a u s e the c h a n g e of
s t a t e of A uCu a l l o y b r i n g s a b o u t o n l y a v e r y s m a l l c h a n g e , l e s s t h a n I . 4 ~ , i n the v o l t a g e / a t o m ( 6 )
608
DIFFUSION OF Cu IN AuCu ALLOY
in the two s t r u c t u r e s .
Vol. 4, No. 8
The d i f f u s i v i t y of Cu in the d i s o r d e r e d AuCu a l l o y was found to be about
4 t i m e s that in the o r d e r e d s t a t e and t h i s m a y be the r e a s o n for the e x i s t e n c e of p s e u d o e q u l I i b r l u m b e t w e e n Cu and o r d e r e d AuCu at t e m p e r a t u r e s l o w e r than the c r i t i c a l t e m p e r a t u r e 380°C. H o w e v e r , the w o r k of J o r d a n and Duwez i n d i c a t e that e v e n when s i n t e r i n g t e m p e r a t u r e s w e r e b e t w e e n 410°C and 450°C, c l e a r l y in the d i s o r d e r e d r a n g e , the p s e u d o e q u i U b r i u m p e r s i s ted b e t w e e n C u a n d A u C u .
The p r e s e n t date i n d i c a t e [ D ] 4 5 0 o C ~ 1 . 8 [ D ] 4 1 0 o c ; the
change
is p r o b a b l y too s m a l l to a c c o u n t for the d i s a p p e a r a n c e of the p s e u d o e q u i l i b r i u m j u s t above 450°C. It i s t r u e that the AuCu a l l o y l o s e s i t s long r a n g e o r d e r c o m p l e t e l y at 408°C but upto a r e a s o n a b l y high t e m p e r a t u r e ,
upto about 5Z5°C,
s h o r t r a n g e o r d e r p e r s l s t s ( 7 ) i n It.
Sykes
and
Jones (8, 9) studied the k i n e t i c s of o r d e r in Cu~Au a l l o y and o b s e r v e d that the r a t e of o r d e r i n g was v e r y slow.
It was s u g g e s t e d that the slow r a t e of a t o m i c m i g r a t i o n in Cu3Au was r e l a t e d to
the p r e s e n c e of s h o r t r a n g e o r d e r , a n t i p h a s e d o m a i n s , in the a l l o y . Since the s h o r t r a n g e o r d e r in AuCu i s quite p r o m i n e n t j u s t above the c r i t i c a l t e m p e r a t u r e (7) it is p o s s i b l e that the d i f f u s i v i t y of Gu in d i s o r d e r e d AuCu in the t e m p e r a t u r e r a n g e of 408°C to 450°C is c o m p a r a t i v e l y l o w e r than t h a t obtained by e x t r a p o l a t i o n of the high t e m p e r a t u r e d i f f u s i o n data and hence the p e r s i s t e n c e of the p s e u d o e q u i l i b r i u m upto 450°C.
On the o t h e r h~nd d l f f u s i o n o f C u i n A u i s
e x p e c t e d to p r o d u c e A u r i c h s o l u t i o n at the i n t e r f a c e and with p r o g r e s s of d i f f u s i o n the i n t e r f a c e is e x p e c t e d to p a s s ,
some t i m e or o t h e r , through the Cu3A u c o m p o s i t i o n .
The e x i s t i n g l i t e r a -
t u r e data (I0~ shows that the d i f f u s i v i t y o f C u i n Au3Cu a l l o y a t 4 4 6 ° G i s about 2 . 6 x l 0 " I Z c m Z / s e c , which at the s a m e t e m p e r a t u r e is about two o r d e r s of m a g n i t u d e s m a l l e r than the d l f f u s i v i t y of Gu in d i s o r d e r e d A u C u a l l o y .
It i s r a t h e r s u r p r i s i n g that i n s p i r e of the low d l f f u s i v l t y of Cu in
Au3Cu d i f f u s i o n of Cu i n A u p r o g r e s s e s
to p r o d u c e AuCu a l l o y w h e r e a s with r e l a t i v e l y l a r g e
d i H u s i v l t y of Cu in the d i s o r d e r e d A u G u d i f f u s i o n of Gu in Au stops as AuCu c o m p o s i t i o n i s attained.
T h u s i t a p p e a r s that the o r i g i n of the p s e u d o e q u i l l b r i u m i n A u - C u c o m p a c t is m o r e
c o m p l e x than could be e x p l a i n e d on the b a s i s of the phase s t a b i l i t y a l o n e .
Vol.
4, No.
8
DIFFUSION
OF Cu IN A u C u ALLOY
609
REFERENCES
lo
P . D u w e z & G . B . Jordan, T r a n s . A S M , ~41, 194, 1949.
Z.
P . D u w e z , P o w d e r M e t a l l u r g y Bulletin, 4, 144, 1949.
3.
P.Duwez, P o w d e r M e t a l l u r g y Bulletin, 4, 168, 1949.
4.
P . Duwez & C . B . Jordan, l i t h e P h y s i c s of P o w d e r M e t a l l u r g ~ l, McGraw Hill Book Co. New York, 1951.
51
T. B. C r u m p l e r , Anal. C h e m . 19, 3Z5, 1947.
6.
W.B. P e a r s o n , "A Handbook of Lattice Spacings and S t r u c t u r e s of Metals and A11oys", P e r g a m o n P r e s s , New York, 1958.
7.
B . W . R o b e r t s , Acta Met, Z, 597, 1954.
8.
G. Sykes & F . W . Jones, P r o c . Roy. Soc. A157, Z13, 1936.
9.
C. Sykes & F . W . Jones, P r o c . Roy. Soc. A166, 376, 1938.
10.
W. Jost, "Diffusion In Sollds, Liquids, G a s e s " , A c a d e m l c P r e s s , New York, 1952.
METALLURGICA
Vol. 4, pp. 605-610, 1970 Printed in the U n i t e d States
Pergamon
Press,
Inc.
DIFFUSION O F Cu in AuCu A L L O Y M. Khobaih ~ and K . P . G u p t a D e p a r t m e n t of M e t a l l u r g i c a l E n g i n e e r i n g Indian i n s t i t u t e of T e c h n o l o g y , K a n p u r , India ___..-_
(Received
June
19,
1970)
W h e n a powder compact containing two metalpowders
is heated at a given temperature for
sufficiently long time it is expected to produce a h o m o g e n e o u s alloyof appropriate composition. While this appears to be true for isomorphous
binary systems (I) the s a m e does not s e e m to
occur for binary systems involving inter~nediate phases (2, 3) or order disorder transformation (4).
Jordan and D u w e z (4) observed a pseudoequilibrium
phase in sintered powder
compacts
containing 7 5 % C u
between
C u and A u C u ordered
and Z 5 % Au, whereas the s a m e powder
compacts readily produced homogeneous A u C u 3 alloy at temperatures above 450°C.
The pseu-
doequilibrium in C u - A u compacts has beenattrtbuted tothe relative stability of the intermediate ordered phase.
One would then expect to find appreciable difference in the diffusivity of C u i n
the ordered and the disordered A u C u
phases.
In the present
investigation diffusion of C u in
A u C u alloy has been studied. A u C u alloy was prepared by melting 99.999% pure A u and C u in an argon gas atmosphere induction melting unit.
The alloy was remelted
prepare a I/2" dia. rod specimen,
in an evacuated and sealed quartz capsule to
slowly cooled down to 800°C and homogenized at this tem-
perature for 5 hours and finally quenched in cold tap water to retain the disordered structure. This treatment was necessary before cold swaging it into thinner rod. T w o diameter x 5 c m long were prepared
specimens of 5 m m
by turning the swaged alloy on a precision lathe and the
specimens were annealed in evacuated and sealed quartz capsules,
one at 800°C for two days
and the other at 330°C for 7 days, and finally quenched incold tapwater so as to produce the dis-
P r e s e n t a d d r e s s : D e p a r t m e n t of M e t a l l u r g y , U n i v e r s i t y of C o n n e c t i c u t , S t o r r s , Connecticut, U . S . A . 605
ordered and the ordered structures in a bath containing
175 gm/lit
Both specimens
respectively.
CuSO4.5
at bath operating conditions of 4 volts,
H20,
100 gm/lit
15 amp/sq.ft
rature and slow stirring with a magnetic stirrer. coherent,
adherent
and uniform all over.
each
of the
specimens
300°,
325O,
350°,
550°,
625’
and 9 days at 625’
sufficiently wide diffusion
were electroplated
H2SO4 and 20 to 30 gm/lit
current density,
25’ to 30°C
with Cu
Agar and
bath tempe-
The deposited copper was very fine grained,
Three
specimens of 13 mm length were cut from
and 7OO’C.
60 days at 300°C,
and 700°C, zones.
The temperature
especially
The annealed
at the lower temperatures specimens
turned from the specimen for chemical analysis. of Cu by calorimetric
lable for each depth of cut,
control was better than+
45 days at 325’ and 350°C,
were
depth of 1 mm for the ordered state and 2 mm for the disordered
with the analysis
4, No.8
and diffusion annealed in evacuated and sealed quarts capsules
Long diffusion times were allowed, 550°C
Vol.
DIFFUSION OF Cu IN AuCu ALLOY
606
1°C.
20 days at
as to produce
faced off from one end toa
state before
Since the presence
methodand onlya few milligrams
the calorimetric
so
at
thin layers were
of Au does not interfere of turnings were avai-
analysis was found most suitable and accurate for
the present investigation.
All chemical analysis of Cu were done by a Bausch 81 Lomb Spectro-
nit 20 spectrocolorimeter
using a 2% aqueous solution of ethylene diamine as the coloring agent
which has been claimed three times
more
sensitive
FIG.
than the usually used reagent
1
Concentration Profile of Cu in a Cu/AuCu Diffusion Couple at Annealing Temperature 350°C and Annealing Time 1080 hours.
NH4OH. (5).
Vol.
4, No.
8
DIFFUSION
OF Cu IN A u C u ALLOY
607
A typical copper concentration profile obtained in t~e present investigation is shown in Fig.
I.
The diffusion coefficient calculations
were done by the standard B o l t z m a n n - M a t a n o
method and the diffusion data for the six specimens plotted as logl0D against I/T,
Fig. 2, gave the values of D o and Q for the two states of A u C u TABLE
Diffusion Data for C u / A u C u State of AuCu alloy
Disordered
Ordered
are shown in Table I. The results w h e n
Temperature i n OK
1
Couple at Various Temperatures
Diffusivity, D in cmZ/sec
973
1.94 x 10 -9
898
1.01 x I0 "9
823
5.35
623
1 . 2 0 x 10 -11
598
8.75 x 10 -12
573
5.83 x I0 "12
x
DO in cmZ/sec
Activation Energy, Q in K. C a l / g m . a t o m
Z.36 x 10 -6
13.63
7.94 x 10 -8
10.72
10 - 1 0
iI FIG. 2 LoglOD a s a F u n c t i o n of I / T f o r the O r d e r e d and D i s o r d e r e d States of A u C u . alloy.
I t a p p e a r s f r o m the
results
a c t i v a t i o n e n e r g y for d i f f u s i o n of C u .
t h a t the
two s t a t e s of A u C u a l l o y h a v e a l m o s t the s a m e
T h i s p r o b a b l y i s n o t s u r p r i s i n g b e c a u s e the c h a n g e of
s t a t e of A uCu a l l o y b r i n g s a b o u t o n l y a v e r y s m a l l c h a n g e , l e s s t h a n I . 4 ~ , i n the v o l t a g e / a t o m ( 6 )
608
DIFFUSION OF Cu IN AuCu ALLOY
in the two s t r u c t u r e s .
Vol. 4, No. 8
The d i f f u s i v i t y of Cu in the d i s o r d e r e d AuCu a l l o y was found to be about
4 t i m e s that in the o r d e r e d s t a t e and t h i s m a y be the r e a s o n for the e x i s t e n c e of p s e u d o e q u l I i b r l u m b e t w e e n Cu and o r d e r e d AuCu at t e m p e r a t u r e s l o w e r than the c r i t i c a l t e m p e r a t u r e 380°C. H o w e v e r , the w o r k of J o r d a n and Duwez i n d i c a t e that e v e n when s i n t e r i n g t e m p e r a t u r e s w e r e b e t w e e n 410°C and 450°C, c l e a r l y in the d i s o r d e r e d r a n g e , the p s e u d o e q u i U b r i u m p e r s i s ted b e t w e e n C u a n d A u C u .
The p r e s e n t date i n d i c a t e [ D ] 4 5 0 o C ~ 1 . 8 [ D ] 4 1 0 o c ; the
change
is p r o b a b l y too s m a l l to a c c o u n t for the d i s a p p e a r a n c e of the p s e u d o e q u i l i b r i u m j u s t above 450°C. It i s t r u e that the AuCu a l l o y l o s e s i t s long r a n g e o r d e r c o m p l e t e l y at 408°C but upto a r e a s o n a b l y high t e m p e r a t u r e ,
upto about 5Z5°C,
s h o r t r a n g e o r d e r p e r s l s t s ( 7 ) i n It.
Sykes
and
Jones (8, 9) studied the k i n e t i c s of o r d e r in Cu~Au a l l o y and o b s e r v e d that the r a t e of o r d e r i n g was v e r y slow.
It was s u g g e s t e d that the slow r a t e of a t o m i c m i g r a t i o n in Cu3Au was r e l a t e d to
the p r e s e n c e of s h o r t r a n g e o r d e r , a n t i p h a s e d o m a i n s , in the a l l o y . Since the s h o r t r a n g e o r d e r in AuCu i s quite p r o m i n e n t j u s t above the c r i t i c a l t e m p e r a t u r e (7) it is p o s s i b l e that the d i f f u s i v i t y of Gu in d i s o r d e r e d AuCu in the t e m p e r a t u r e r a n g e of 408°C to 450°C is c o m p a r a t i v e l y l o w e r than t h a t obtained by e x t r a p o l a t i o n of the high t e m p e r a t u r e d i f f u s i o n data and hence the p e r s i s t e n c e of the p s e u d o e q u i l i b r i u m upto 450°C.
On the o t h e r h~nd d l f f u s i o n o f C u i n A u i s
e x p e c t e d to p r o d u c e A u r i c h s o l u t i o n at the i n t e r f a c e and with p r o g r e s s of d i f f u s i o n the i n t e r f a c e is e x p e c t e d to p a s s ,
some t i m e or o t h e r , through the Cu3A u c o m p o s i t i o n .
The e x i s t i n g l i t e r a -
t u r e data (I0~ shows that the d i f f u s i v i t y o f C u i n Au3Cu a l l o y a t 4 4 6 ° G i s about 2 . 6 x l 0 " I Z c m Z / s e c , which at the s a m e t e m p e r a t u r e is about two o r d e r s of m a g n i t u d e s m a l l e r than the d l f f u s i v i t y of Gu in d i s o r d e r e d A u C u a l l o y .
It i s r a t h e r s u r p r i s i n g that i n s p i r e of the low d l f f u s i v l t y of Cu in
Au3Cu d i f f u s i o n of Cu i n A u p r o g r e s s e s
to p r o d u c e AuCu a l l o y w h e r e a s with r e l a t i v e l y l a r g e
d i H u s i v l t y of Cu in the d i s o r d e r e d A u G u d i f f u s i o n of Gu in Au stops as AuCu c o m p o s i t i o n i s attained.
T h u s i t a p p e a r s that the o r i g i n of the p s e u d o e q u i l l b r i u m i n A u - C u c o m p a c t is m o r e
c o m p l e x than could be e x p l a i n e d on the b a s i s of the phase s t a b i l i t y a l o n e .
Vol.
4, No.
8
DIFFUSION
OF Cu IN A u C u ALLOY
609
REFERENCES
lo
P . D u w e z & G . B . Jordan, T r a n s . A S M , ~41, 194, 1949.
Z.
P . D u w e z , P o w d e r M e t a l l u r g y Bulletin, 4, 144, 1949.
3.
P.Duwez, P o w d e r M e t a l l u r g y Bulletin, 4, 168, 1949.
4.
P . Duwez & C . B . Jordan, l i t h e P h y s i c s of P o w d e r M e t a l l u r g ~ l, McGraw Hill Book Co. New York, 1951.
51
T. B. C r u m p l e r , Anal. C h e m . 19, 3Z5, 1947.
6.
W.B. P e a r s o n , "A Handbook of Lattice Spacings and S t r u c t u r e s of Metals and A11oys", P e r g a m o n P r e s s , New York, 1958.
7.
B . W . R o b e r t s , Acta Met, Z, 597, 1954.
8.
G. Sykes & F . W . Jones, P r o c . Roy. Soc. A157, Z13, 1936.
9.
C. Sykes & F . W . Jones, P r o c . Roy. Soc. A166, 376, 1938.
10.
W. Jost, "Diffusion In Sollds, Liquids, G a s e s " , A c a d e m l c P r e s s , New York, 1952.