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Effect of magnetic transformation on creep behavior of a nickel-cobalt alloy
Scripta
METALLURGICA
Vol. 5~ pp. 8 2 5 - 8 2 8 , 1971 P r i n t e d in the U n i t e d S t a t e s
Pergamon
Press,
Inc
EFFECT OF MAGNETIC TRANSFORMATION ON CREEP BEHAVIOR OF A NICKEL-COBALT ALLOY
H. 0ikawa, K. Oguchi and S. Karashima Department of Materials Science Tohoku University Sendai, Japan
(Received
June
28,
1971)
Influence of magnetic transformation on diffusion has been observed in bcc iron and iron-base solid solutions and in fcc nickel-cobalt alloys(l).
Similar influence of
magnetic transformation on creep behavior was suggested by Garofalo(2) and was found by Karashima et al.(3) on the steady-state creep rates in alpha-iron.
Many investigators
have reported the same effect on iron(4,5) and iron-base solid solutions such as Fe-Si(6~8)~ Fe-Cr(9), Fe-Co(7), and Fe-Mo(7,10) systems.
Direct comparison of the magnetic effect
between diffusion and creep has been done only on pure iron(4,5,11,12)
and Fe-Cr alloys(9,13).
In fcc metals and alloys, similar magnetic effect on creep has been suggested in a few investigations on nickel(14,15) and Ni-Fe alloys(16).
No diffusion data, however, on
these fcc metal and alloys are available in the ferromagnetic temperature region. In this paper creep behavior of a fcc alloy, in which diffusion data have been reported, near the magnetic Curie temperature is reported.
The material used was a nickel-cobalt alloy containing 50 at.% cobalt made by vacuummelting of pure nickel(99.95+ %) and pure cobalt(99.8+ %).
Specimens, the gage length and
the width of which were 50 mm and 5 mm respectively, were machined from a sheet of 1 mm in thickness. greep tests were carried out in argon atmosphere under constant tensile stress in the temperature range 730 ° to I030°C.
Testing apparatus and test procedure were reported in
detail elsewhere(7).
Temperature dependence of the steady-state is clearly
seen that
the alloy,
that
creep,
~ , i s shown i n F i g . 1. It s the slope of curves changes in the vicinity of the Curie temperature of
is about 850°C(17).
T h i s phenomenon, t h e s o - c a l l e d
can be compared w i t h t h e s e l f - d i f f u s i o n
cobalt alloy(18).
creep rate,
data of nickel
Both c u r v e s c h a n g e t h e i r
magnetic effect
and c o b a l t
in nickei-49
s l o p e s a t a b o u t t h e same t e m p e r a t u r e .
825
on at.%
826
MAGNETIC
TRANSFORMATION
The ratio, A~f/~ p s s = (~p - ~f)/
AND CREEP OF Ni-Co A L L O Y
Vol.
5, No.
I0
~p' where ~fs is the observed value at a temperature in
the ferromagnetic region and ~P the value at that temperature estimated by the extrapolation s of the observed values in the parama~netic region, is 0.25 for o = 2.5 kg/mm 2 and 0.35 for o = 4 kg/mm 2.
1000 10~'1 ' i
],
I":',. 10"~
Temp. ('C) 900 800 700 ~ i ' , ' 10"10 \ ~ Ni-50Co o.~_ a g~ 0.27ram \'~o. • as 045mm \%~0" N.~\?~g.s.O.4Omm 10" .
,~
The r a t i o
is only a half
of the corresponding ratios for selff p f p d i f f u s i o n , ~DNi/DNi and ADco/Dco , which are about 0.55.
On t h e o t h e r hand, i t
was found t h a t t h e s e r a t i o s
were a l m o s t
t h e same w i t h each o t h e r i n a l p h a - i r o n ( 7 ) . The t e m p e r a t u r e a t which t h e changes in the slope of curves f o r creep occur is close to that for diffusion, though t h e f o r m e r t e n d s t o s h i f t
slightly
t o lower t e m p e r a t u r e as t h e a p p l i e d s t r e s s increases.
In a l p h a - i r o n t h e c r i t i c a l
E
U
t e m p e r a t u r e f o r c r e e p a p p a r e n t l y lower
o
than that for diffusion(7). Whether t h e d i s c r e p a n c y i n t h e
T¢ l
16
I 8
magnetic effects
\
t h e p r e s e n t a l l o y comes from t h e n a t u r e o f
%•
i
I ,"'h 9 lIT (10"4K °l )
b e t w e e n a l p h a - i r o n and
the crystal
I 10
s y s t e m s o r from t h e i r
characteristics
own
i s one o f t h e most
i m p o r t a n t p r o b l e m s t o be s o l v e d .
To
discuss the discrepancy in detail,
FIG. 1 T e m p e r a t u r e Dependence o f t h e S t e a d y - S t a t e Creep R a t e , ~ , o f Ni-50Co A l l o y . Diffusion S Data a r e t a k e n from Those g i v e n by Hirano et a1.(18).
it
n e c e s s a r y t o make c l e a r many f a c t o r s , as t h e e l a s t i c fault
is such
modulus and t h e s t a c k i n g
energy of this
alloy at high
temperature.
The a c t i v a t i o n
e n e r g y f o r c r e e p c o m p e n s a t e d f o r e l a s t i c - m o d u l u s c h a n g e , Q~, was
e s t i m a t e d by t h e e q u a t i o n ( 1 9 ) , n ~s
(+T)
exp(-
where o i s t h e a p p l i e d s t r e s s direct
Q' c and ET t h e Youngs modulus a t t e s t i n g
temperature.
S i n c e no
measurement has b e e n done on ET a t h i g h t e m p e r a t u r e , a v e r a g e v a l u e o f t h o s e f o r p u r e
n i c k e l and p u r e c o b a l t a t each t e m p e r a t u r e ( 2 0 ) was u s e d as ET f o r t h i s magnetic effect
on ET f o r t h i s a l l o y i s t a k e n i n t o a c c o u n t ( 2 1 ) .
was S.5 i n b o t h t e m p e r a t u r e r e g i o n s . with the activation
The v a l u e s o f Q~ a r e l i s t e d
energies for self-diffusion
of nickel,
1:1 a l l o y .
The s t r e s s
No
e x p o n e n t , ~,
i n T a b l e 1, t o g e t h o r
q N i ' and c o b a l t ,
QEo' o b t a i n e d on
Vol.
5, No.
I0
MAGNETIC
TRANSFORMATION
a nickel-49 at.% cobalt alloy(18).
AND
CREEP
OF N i - C o
Alloy
827
As seen in the table, the values of Qc are almost the
same in both temperature regions and are in good agreement with QNi and Qco"
TABLE 1 Modulus-Compensated Activation Energy for Creep and Activation Energies(18) for Self-Diffusion of the Constituent Elements Creep of Ni-50Co alloy o/E T
0.94x10 -4
1.61xlO -4
2.51xi0-4
Self-diffusion in Ni-49Co alloy(18)
Temperature
Q~
Temperature
QNi
Qco
(°c)
(kcal/mol)
(°C)
(kcal/mol)
(kcal/mol)
870~i030
62.9±6.4*
730 ~850
53.6±3.6
701 ~819
63.7±8.3*
61.6±5.5"
870 ~930
57.4±4.4
730 ~800
58.8±8.2
899~I192
61.3±5.5
60.0±0.7
830 ~870
59.8±3.0
* The limit refers to 95% confidence limit.
From the results mentioned above it is concluded that the magnetic effect on creep, which originates from the magnetic effect on diffusion, is a general feature in both fcc and bcc metals and alloys.
References (i)
R.J.
Borg; "Diffusion in Body-Centered Cubic Metals", p. 225. A. S. M., 0hio(1965).
(2)
F. Garofalo; "Fundamentals of Creep and Creep Rupture in Metals", p. 99. MacMillan, New York (1965).
(3)
S. Karashima, H. Oikawa and T. Watanabe; Acta Met., 14, 791(1966).
(4)
Y. Ishida, C. Y. Cheng and J. E. Dorn; Trans. Met. Soc. AIME, 236, 964(1966).
(S)
J. Cadek, M. Pahutov~, K. Ciha and T. Hostinsky; Acta Met., 17, 803(1969).
(6)
C . Y . Cheng, A. Karim, T. G. Langdon and J. E. Dorn; Trans. Met. Soc. AIME, 242, 890(1968).
(7)
S. Karashima, H. Oikawa and T. Watanabe; T r a n s . Met. Soe. AIME, 242, 1 7 0 3 ( 1 9 6 8 ) .
(8)
A. Karim; Canad. d. P h y s . , 4 6 , 2 4 2 5 ( 1 9 6 8 ) .
(9)
Y. Imai and T. M u r a t a ; d. J a p a n I n s t .
(10)
A. Fuchs and B. I l s c h n e r ;
(11)
F. S. B u f f i n g t o n ,
(12)
D. W. dames and G. M. Leak; P h i l .
M e t a l s , 29, 1 0 5 3 ( 1 9 6 5 ) .
A c t a M e t . , 17, 7 0 1 ( 1 9 6 9 ) .
K. H i r a n o and M. Cohen; Acta M e t . , 9 , 4 3 4 ( 1 9 6 1 ) . Mag., 1 4 , 7 0 1 ( 1 9 6 6 ) .
828
MAGNETIC
TRANSFORMATION
AND
CREEP
OF N i - C o A L L O Y
Vol.
5, No.
(13)
S. P. Ray and B. D. Sharma; Acta Met., 16, 981(1968).
(14)
P. R. Landon, J. L. Lytton, L. A. Shepard and J. E. Dorn; Trans. ASM, 51, 900(1959).
(15)
E. C. Norman and S. A. Duran; Acta Met., 18, 723(1970).
(16)
S. Karashima, T. Motomiya and H. Oikawa; Tech. Repts., Tohoku Univ., 33, 193(1968).
(17)
M. Hansen and K. Anderko; "Constitution of Binary Alloys", p. 485. McGraw-Hill, New York(1958).
(18)
K. Hirano, R. P. Agarwala, B. L. Averbach and M. Cohen; J. Appl. Phys., 33, 3049(1962).
(19)
O. D. Sherby; Acta Met., iO, 135(1962).
(20)
W. KOster; Z. Metallk., 89, I(1948).
(21)
K. T. Kamber; Dissertation, Stanford Univ. (1963).
i0
METALLURGICA
Vol. 5~ pp. 8 2 5 - 8 2 8 , 1971 P r i n t e d in the U n i t e d S t a t e s
Pergamon
Press,
Inc
EFFECT OF MAGNETIC TRANSFORMATION ON CREEP BEHAVIOR OF A NICKEL-COBALT ALLOY
H. 0ikawa, K. Oguchi and S. Karashima Department of Materials Science Tohoku University Sendai, Japan
(Received
June
28,
1971)
Influence of magnetic transformation on diffusion has been observed in bcc iron and iron-base solid solutions and in fcc nickel-cobalt alloys(l).
Similar influence of
magnetic transformation on creep behavior was suggested by Garofalo(2) and was found by Karashima et al.(3) on the steady-state creep rates in alpha-iron.
Many investigators
have reported the same effect on iron(4,5) and iron-base solid solutions such as Fe-Si(6~8)~ Fe-Cr(9), Fe-Co(7), and Fe-Mo(7,10) systems.
Direct comparison of the magnetic effect
between diffusion and creep has been done only on pure iron(4,5,11,12)
and Fe-Cr alloys(9,13).
In fcc metals and alloys, similar magnetic effect on creep has been suggested in a few investigations on nickel(14,15) and Ni-Fe alloys(16).
No diffusion data, however, on
these fcc metal and alloys are available in the ferromagnetic temperature region. In this paper creep behavior of a fcc alloy, in which diffusion data have been reported, near the magnetic Curie temperature is reported.
The material used was a nickel-cobalt alloy containing 50 at.% cobalt made by vacuummelting of pure nickel(99.95+ %) and pure cobalt(99.8+ %).
Specimens, the gage length and
the width of which were 50 mm and 5 mm respectively, were machined from a sheet of 1 mm in thickness. greep tests were carried out in argon atmosphere under constant tensile stress in the temperature range 730 ° to I030°C.
Testing apparatus and test procedure were reported in
detail elsewhere(7).
Temperature dependence of the steady-state is clearly
seen that
the alloy,
that
creep,
~ , i s shown i n F i g . 1. It s the slope of curves changes in the vicinity of the Curie temperature of
is about 850°C(17).
T h i s phenomenon, t h e s o - c a l l e d
can be compared w i t h t h e s e l f - d i f f u s i o n
cobalt alloy(18).
creep rate,
data of nickel
Both c u r v e s c h a n g e t h e i r
magnetic effect
and c o b a l t
in nickei-49
s l o p e s a t a b o u t t h e same t e m p e r a t u r e .
825
on at.%
826
MAGNETIC
TRANSFORMATION
The ratio, A~f/~ p s s = (~p - ~f)/
AND CREEP OF Ni-Co A L L O Y
Vol.
5, No.
I0
~p' where ~fs is the observed value at a temperature in
the ferromagnetic region and ~P the value at that temperature estimated by the extrapolation s of the observed values in the parama~netic region, is 0.25 for o = 2.5 kg/mm 2 and 0.35 for o = 4 kg/mm 2.
1000 10~'1 ' i
],
I":',. 10"~
Temp. ('C) 900 800 700 ~ i ' , ' 10"10 \ ~ Ni-50Co o.~_ a g~ 0.27ram \'~o. • as 045mm \%~0" N.~\?~g.s.O.4Omm 10" .
,~
The r a t i o
is only a half
of the corresponding ratios for selff p f p d i f f u s i o n , ~DNi/DNi and ADco/Dco , which are about 0.55.
On t h e o t h e r hand, i t
was found t h a t t h e s e r a t i o s
were a l m o s t
t h e same w i t h each o t h e r i n a l p h a - i r o n ( 7 ) . The t e m p e r a t u r e a t which t h e changes in the slope of curves f o r creep occur is close to that for diffusion, though t h e f o r m e r t e n d s t o s h i f t
slightly
t o lower t e m p e r a t u r e as t h e a p p l i e d s t r e s s increases.
In a l p h a - i r o n t h e c r i t i c a l
E
U
t e m p e r a t u r e f o r c r e e p a p p a r e n t l y lower
o
than that for diffusion(7). Whether t h e d i s c r e p a n c y i n t h e
T¢ l
16
I 8
magnetic effects
\
t h e p r e s e n t a l l o y comes from t h e n a t u r e o f
%•
i
I ,"'h 9 lIT (10"4K °l )
b e t w e e n a l p h a - i r o n and
the crystal
I 10
s y s t e m s o r from t h e i r
characteristics
own
i s one o f t h e most
i m p o r t a n t p r o b l e m s t o be s o l v e d .
To
discuss the discrepancy in detail,
FIG. 1 T e m p e r a t u r e Dependence o f t h e S t e a d y - S t a t e Creep R a t e , ~ , o f Ni-50Co A l l o y . Diffusion S Data a r e t a k e n from Those g i v e n by Hirano et a1.(18).
it
n e c e s s a r y t o make c l e a r many f a c t o r s , as t h e e l a s t i c fault
is such
modulus and t h e s t a c k i n g
energy of this
alloy at high
temperature.
The a c t i v a t i o n
e n e r g y f o r c r e e p c o m p e n s a t e d f o r e l a s t i c - m o d u l u s c h a n g e , Q~, was
e s t i m a t e d by t h e e q u a t i o n ( 1 9 ) , n ~s
(+T)
exp(-
where o i s t h e a p p l i e d s t r e s s direct
Q' c and ET t h e Youngs modulus a t t e s t i n g
temperature.
S i n c e no
measurement has b e e n done on ET a t h i g h t e m p e r a t u r e , a v e r a g e v a l u e o f t h o s e f o r p u r e
n i c k e l and p u r e c o b a l t a t each t e m p e r a t u r e ( 2 0 ) was u s e d as ET f o r t h i s magnetic effect
on ET f o r t h i s a l l o y i s t a k e n i n t o a c c o u n t ( 2 1 ) .
was S.5 i n b o t h t e m p e r a t u r e r e g i o n s . with the activation
The v a l u e s o f Q~ a r e l i s t e d
energies for self-diffusion
of nickel,
1:1 a l l o y .
The s t r e s s
No
e x p o n e n t , ~,
i n T a b l e 1, t o g e t h o r
q N i ' and c o b a l t ,
QEo' o b t a i n e d on
Vol.
5, No.
I0
MAGNETIC
TRANSFORMATION
a nickel-49 at.% cobalt alloy(18).
AND
CREEP
OF N i - C o
Alloy
827
As seen in the table, the values of Qc are almost the
same in both temperature regions and are in good agreement with QNi and Qco"
TABLE 1 Modulus-Compensated Activation Energy for Creep and Activation Energies(18) for Self-Diffusion of the Constituent Elements Creep of Ni-50Co alloy o/E T
0.94x10 -4
1.61xlO -4
2.51xi0-4
Self-diffusion in Ni-49Co alloy(18)
Temperature
Q~
Temperature
QNi
Qco
(°c)
(kcal/mol)
(°C)
(kcal/mol)
(kcal/mol)
870~i030
62.9±6.4*
730 ~850
53.6±3.6
701 ~819
63.7±8.3*
61.6±5.5"
870 ~930
57.4±4.4
730 ~800
58.8±8.2
899~I192
61.3±5.5
60.0±0.7
830 ~870
59.8±3.0
* The limit refers to 95% confidence limit.
From the results mentioned above it is concluded that the magnetic effect on creep, which originates from the magnetic effect on diffusion, is a general feature in both fcc and bcc metals and alloys.
References (i)
R.J.
Borg; "Diffusion in Body-Centered Cubic Metals", p. 225. A. S. M., 0hio(1965).
(2)
F. Garofalo; "Fundamentals of Creep and Creep Rupture in Metals", p. 99. MacMillan, New York (1965).
(3)
S. Karashima, H. Oikawa and T. Watanabe; Acta Met., 14, 791(1966).
(4)
Y. Ishida, C. Y. Cheng and J. E. Dorn; Trans. Met. Soc. AIME, 236, 964(1966).
(S)
J. Cadek, M. Pahutov~, K. Ciha and T. Hostinsky; Acta Met., 17, 803(1969).
(6)
C . Y . Cheng, A. Karim, T. G. Langdon and J. E. Dorn; Trans. Met. Soc. AIME, 242, 890(1968).
(7)
S. Karashima, H. Oikawa and T. Watanabe; T r a n s . Met. Soe. AIME, 242, 1 7 0 3 ( 1 9 6 8 ) .
(8)
A. Karim; Canad. d. P h y s . , 4 6 , 2 4 2 5 ( 1 9 6 8 ) .
(9)
Y. Imai and T. M u r a t a ; d. J a p a n I n s t .
(10)
A. Fuchs and B. I l s c h n e r ;
(11)
F. S. B u f f i n g t o n ,
(12)
D. W. dames and G. M. Leak; P h i l .
M e t a l s , 29, 1 0 5 3 ( 1 9 6 5 ) .
A c t a M e t . , 17, 7 0 1 ( 1 9 6 9 ) .
K. H i r a n o and M. Cohen; Acta M e t . , 9 , 4 3 4 ( 1 9 6 1 ) . Mag., 1 4 , 7 0 1 ( 1 9 6 6 ) .
828
MAGNETIC
TRANSFORMATION
AND
CREEP
OF N i - C o A L L O Y
Vol.
5, No.
(13)
S. P. Ray and B. D. Sharma; Acta Met., 16, 981(1968).
(14)
P. R. Landon, J. L. Lytton, L. A. Shepard and J. E. Dorn; Trans. ASM, 51, 900(1959).
(15)
E. C. Norman and S. A. Duran; Acta Met., 18, 723(1970).
(16)
S. Karashima, T. Motomiya and H. Oikawa; Tech. Repts., Tohoku Univ., 33, 193(1968).
(17)
M. Hansen and K. Anderko; "Constitution of Binary Alloys", p. 485. McGraw-Hill, New York(1958).
(18)
K. Hirano, R. P. Agarwala, B. L. Averbach and M. Cohen; J. Appl. Phys., 33, 3049(1962).
(19)
O. D. Sherby; Acta Met., iO, 135(1962).
(20)
W. KOster; Z. Metallk., 89, I(1948).
(21)
K. T. Kamber; Dissertation, Stanford Univ. (1963).
i0