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Irradiation softening and hardening of Ni3Al
Scripta METALLURGICA
Vol. 2, pp. 331-333, 1968 P r i n t e d i n the U n i t e d S t a t e s
Pergamon Press,
IRRADIATION SOFTENING AND HARDENING OF NisAI ~t
Kanji Ono and K.R.Nelson Department of E n g i n e e r i n g U n i v e r s i t y of C a l i f o r n i a Los Angeles, C a l i f o r n i a
( R e c e i v e d April 17, 1968)
An i n t e r m e t a l l i c compound, Ni3AI , has an ordered £ . c . c . s t r u c t u r e o£ type LI2, and shows p e c u l i a r dependence of the y i e l d s t r e s s upon t e s t t e m p e r a t u r e ; i . e . ,
the
y i e l d s t r e s s i n c r e a s e s by a f a c t o r of s i x upon r a i s i n g t e s t temperature from 77"K t o 90O'K ( 1 , 2 ) .
Several mechanisms have been proposed but t h i s b e h a v i o r i s s t i l l
f u l l y understood.
Since i t s c r i t i c a l
not
o r d e r i n g temperature i s a p p a r e n t l y c l o s e to the
m e l t i n g p o i n t , the e f f e c t of d i s o r d e r i n g on the y i e l d s t r e s s of Ni3AI i s not known. I r r a d i a t i o n of ordered s o l i d s o l u t i o n s produces d i s o r d e r i n g i n a d d i t i o n to p o i n t d e f e c t s and t h e i r c l u s t e r s (5).
However, l i t t l e
i s known of the e f f e c t s of i r r a d i a t i o n
on the y i e l d s t r e s s of ordered s o l i d s o l u t i o n s . In the p r e s e n t work, p o l y c r y s t a l l i n e sheet specimens o£ o f f - s t o i c h i o ~ e t r i c NisAI were i r r a d i a t e d with 6 MeV e l e c t r o n s a t room t e m p e r a t u r e .
The specimens were cut from
large c r y s t a l s ÷, r o l l e d to 30% r e d u c t i o n i n t h i c k n e s s , r e c r y s t a l l i z e d a t 1100"C f o r S hours i n vacuum £ollowed by £urnace c o o l i n g , and £ i n a l l y e l e c t r i c a l - d i s c h a r g e - m a c h i n e d to dimensions 45 by 5 by 0 . S m . average composition of 8?.55% Ni.
Grain s i z e was 0 . 0 6 ~ .
Chemical a n a l y s i s gave an
An I n s t r o n t e s t i n g machine was used f o r t e n s i l e
t e s t s . The t e n s i l e s t r a i n r a t e was 5.5 x 1o-Ssec -1. The y i e l d s t r e s s at 0.01~ o f f s e t of u n i r r a d i a t e d NisA1 was 15.6 kg/mm2 a t 500°K and 14.8 kg/mm2 at 77°K, r e s p e c t i v e l y .
The y i e l d s t r e s s of i r r a d i a t e d specimens i n -
creased with i n c r e a s i n g e l e c t r o n dose, when these were t e s t e d a t 77°K. ( I r r a d i a t i o n hardening).
On the o t h e r hand, the y i e l d s t r e s s became s m a l l e r upon i r r a d i a t i o n when
i r r a d i a t e d specimens were t e s t e d a t 500°K ( I r r a d i a t i o n s o f t e n i n g ) .
*
This r e s e a r c h was supported by NASA through UCLA Space Science Center. Now a t Aeronutronic D i v i s i o n , Philco-Ford C o r p o r a t i o n , Newport Beach, C a l i £ o r n i a .
÷
Supplied generously by Dr. B.H. Kear of P r a t t and Whitney A i r c r a f t , North Haven, Connecticut.
331
Inc
332
IRRADIATION SOFTENING AND HARDENING OF Ni/~l
Vol. 2, No. 6
+
TEST AT
E
ja ,o z
"/
Figure 1. Change in the y i e l d s t r e s s o f NisAI i r r a d i a t e d with 6 HeV e l e c t r o n s a t room temperature a g a i n s t e l e c t r o n dose.
5 o
I I I O.S 1.0 I.S e.~C'r,llON ~ {lO"rll/ cm z}
-IO
Z.O
Changes in the y i e l d s t r e s s are p l o t t e d a g a i n s t e l e c t r o n dose in Fig. i .
The
magnitude o f the i r r a d i a t i o n hardening a t 77"K i s q u i t e l a r g e ; the y i e l d s t r e s s i n c r e a s e d Co t h r e e t i n e s the u n i r r a d i a t e d v a l u e f o l l o w i n g i r r a d i a t i o n to 1.6 x 1017e/ca 2. The e x t e n t o f the i r r a d i a e i o n s o f t e n i n g i s not as g r e a t , but i s s t i l l d e c r e a s e in the y i e l d s t r e s s v i a i r r a d i a t i o n to 1.6 x 1017e/cm 2, an i n c r e a s e in s t r a i n r a t e by a f a c t o r o f 10 caused l i t t l e The change was always l e s s than 0.5% o f the flow s t r e s s .
significant;
30%
In a l l c i r c u m s l a n c e s ,
change in the flow s t r e s s . When t e n s i l e t e s t s were
i n t e r r u p t e d , s t r e s s r e l a x a t i o n was v e r y s m a l l . The nagnitude o f observed e f f e c t s are s u r p r i s i n g l y l a r g e in view o f e l e c t r o n doses employed.
When t h e displacement t h r e s h o l d energy i s assumed to be 20 eV, d i s -
placement cro s s s e c t i o n i s 150 x 10"24c~ 2, 60% o f which r e s u l t s in s i n g l e p o i n t d e f e c t s (4).
Thus, the c o n c e n t r a t i o n o f p o i n t d e f e c t s i s between 5 x 10 -6 and 2 x 10 -5 f o r the
e l e c t r o n doses used h e r e .
I f we f u r S h e r assume t h a t the replacement energy i s o f the
o r d e r of 1 eV, t h e number o f replacements i s s i x times t h a t o f the displacement (5). Considering t h a t ,
in an a v e r a g e , e i g h t bonds are d i s o r d e r e d per r e p l a c e m e n t , i r r a d i a t i o n
induced change in long range o r d e r parameter, S , can be expected to be o f the o r d e r 10 "3.
of
D i s o r d e r i n g i n c r e a s e s th e y i e l d s t r e s s o f some ordered a l l o y s a t low temperatures (6).
However, the magnitude o f $ o f annealed NiSA1 i s about 0.9 (7) and the small change
in $ as p r e d i c t e d f o r the p r e s e n t i r r a d i a t i o n cannot p o s s i b l y e x p l a i n s u b s t a n t i a l changes in the y i e l d s t r e s s o f i r r a d i a t e d NisA1.
Observed i r r a d i a t i o n hardening appears to be
due to the presence o f p o i n t d e f e c t s a n d / o r t h e i r c l u s t e r s .
However, t h e usual d i s p e r s e d
b a r r i e r mechanism cannot be invoked in the absence o f s i g u i f i c a n t s t r a i n r a t e dependence o f the y i e l d s t r e s s still
(8,9).
unknown manner.
understanding.
Point d e f e c t s may c o n t r i b u t e to l a t t i c e
f r i c t i o n s t r e s s in a
C l e a r l y , more e x t e n s i v e study o f t h i s e f f e c t must be made f o r f u l l
Vol. 2, No. 6
IRRADIATION
In the case of the irradiation clusters
are unlikely
very sensitive
SOFTENING
AA'I) H A K D E N L N G
softening
a t 500°K, p o i n t d e f e c t s
t o be a c a u s e o f t h e s o f t e n i n g .
t o t h e s m a l l change i n S, so t h a t
cannot explain the softening.
One p o s s i b l e
Again t h e y i e l d
slight
disordering
contribute alloy
and r e p l a c e m e n t c o l l i s i o n s .
to a dislocation
(11) r e d u c t i o n
drag just
in either
(I0),
NisAl
333
and t h e i r stress
is not
due t o i r r a d i a t i o n
mechanism o f t h e s o f t e n i n g
d o m a i n s " , which h a v e b e e n s u g g e s t e d by a c o m p u t e r e x p e r i m e n t process of displacement
OF
is that
"micro-
are destroyed
in the
Since the micro-domains should
as do G u i n i e r - P r e s t o n
zones i n an a g e - h a r d e n e d
t h e number o r t h e e f f e c t i v e n e s s
of the micro-domains will reduce the yield stress.
as a d i s l o c a t i o n
drag
This softening mechanism is valid
in other partially ordered alloys, so that a similar softening should be observed via further
investigation
using other alloy systems.
References i.
R. G. Davies and N.S. S t o l o f f , Trans. TMS-AI~ 235, 714 (1965).
2.
S. M. Copley and B.H. Kear, Trans. TMS-AI~
5.
A. C. Damask, Studies in Radiation Effects on Solids, Vol. 2, p. 1, Gordon and B r e a c h , New York ( 1 9 6 7 ) .
4.
G. H. Kinchin and R.S. Pease, J. Nucl. Energy I, 200 (1955).
5.
G. J. Dienes and G.H. Vineyard, Radiation Effects in Solids, p. 32 . Interscience, New York (1957).
6.
N. S. Stoloff and R. G. Davies, Progress in Materials Pergamon Press, New York (1966).
7.
C. L. Corey and D. I. Potter, J. Appl. Phys. 58, 5894 (1967).
8.
A. Seeger, Proc. 2nd Int. Conf. PUAE, 6, p.250, United Nations, New York (1958).
9.
K. Ono and M. Meshii, Trans. ASM 60, 426 (1967).
259, 977 (1967).
Sci., Vol. 15, p. 43,
I0. P.C. Gehlen and J. B. Cohen, Phys. Rev. 159, A844 (1965). II. R. W. Cahn, Local Atomic Arrangements Studied by X-ray Diffraction, p. 196. Gordon and Breach, New York (1966).
Vol. 2, pp. 331-333, 1968 P r i n t e d i n the U n i t e d S t a t e s
Pergamon Press,
IRRADIATION SOFTENING AND HARDENING OF NisAI ~t
Kanji Ono and K.R.Nelson Department of E n g i n e e r i n g U n i v e r s i t y of C a l i f o r n i a Los Angeles, C a l i f o r n i a
( R e c e i v e d April 17, 1968)
An i n t e r m e t a l l i c compound, Ni3AI , has an ordered £ . c . c . s t r u c t u r e o£ type LI2, and shows p e c u l i a r dependence of the y i e l d s t r e s s upon t e s t t e m p e r a t u r e ; i . e . ,
the
y i e l d s t r e s s i n c r e a s e s by a f a c t o r of s i x upon r a i s i n g t e s t temperature from 77"K t o 90O'K ( 1 , 2 ) .
Several mechanisms have been proposed but t h i s b e h a v i o r i s s t i l l
f u l l y understood.
Since i t s c r i t i c a l
not
o r d e r i n g temperature i s a p p a r e n t l y c l o s e to the
m e l t i n g p o i n t , the e f f e c t of d i s o r d e r i n g on the y i e l d s t r e s s of Ni3AI i s not known. I r r a d i a t i o n of ordered s o l i d s o l u t i o n s produces d i s o r d e r i n g i n a d d i t i o n to p o i n t d e f e c t s and t h e i r c l u s t e r s (5).
However, l i t t l e
i s known of the e f f e c t s of i r r a d i a t i o n
on the y i e l d s t r e s s of ordered s o l i d s o l u t i o n s . In the p r e s e n t work, p o l y c r y s t a l l i n e sheet specimens o£ o f f - s t o i c h i o ~ e t r i c NisAI were i r r a d i a t e d with 6 MeV e l e c t r o n s a t room t e m p e r a t u r e .
The specimens were cut from
large c r y s t a l s ÷, r o l l e d to 30% r e d u c t i o n i n t h i c k n e s s , r e c r y s t a l l i z e d a t 1100"C f o r S hours i n vacuum £ollowed by £urnace c o o l i n g , and £ i n a l l y e l e c t r i c a l - d i s c h a r g e - m a c h i n e d to dimensions 45 by 5 by 0 . S m . average composition of 8?.55% Ni.
Grain s i z e was 0 . 0 6 ~ .
Chemical a n a l y s i s gave an
An I n s t r o n t e s t i n g machine was used f o r t e n s i l e
t e s t s . The t e n s i l e s t r a i n r a t e was 5.5 x 1o-Ssec -1. The y i e l d s t r e s s at 0.01~ o f f s e t of u n i r r a d i a t e d NisA1 was 15.6 kg/mm2 a t 500°K and 14.8 kg/mm2 at 77°K, r e s p e c t i v e l y .
The y i e l d s t r e s s of i r r a d i a t e d specimens i n -
creased with i n c r e a s i n g e l e c t r o n dose, when these were t e s t e d a t 77°K. ( I r r a d i a t i o n hardening).
On the o t h e r hand, the y i e l d s t r e s s became s m a l l e r upon i r r a d i a t i o n when
i r r a d i a t e d specimens were t e s t e d a t 500°K ( I r r a d i a t i o n s o f t e n i n g ) .
*
This r e s e a r c h was supported by NASA through UCLA Space Science Center. Now a t Aeronutronic D i v i s i o n , Philco-Ford C o r p o r a t i o n , Newport Beach, C a l i £ o r n i a .
÷
Supplied generously by Dr. B.H. Kear of P r a t t and Whitney A i r c r a f t , North Haven, Connecticut.
331
Inc
332
IRRADIATION SOFTENING AND HARDENING OF Ni/~l
Vol. 2, No. 6
+
TEST AT
E
ja ,o z
"/
Figure 1. Change in the y i e l d s t r e s s o f NisAI i r r a d i a t e d with 6 HeV e l e c t r o n s a t room temperature a g a i n s t e l e c t r o n dose.
5 o
I I I O.S 1.0 I.S e.~C'r,llON ~ {lO"rll/ cm z}
-IO
Z.O
Changes in the y i e l d s t r e s s are p l o t t e d a g a i n s t e l e c t r o n dose in Fig. i .
The
magnitude o f the i r r a d i a t i o n hardening a t 77"K i s q u i t e l a r g e ; the y i e l d s t r e s s i n c r e a s e d Co t h r e e t i n e s the u n i r r a d i a t e d v a l u e f o l l o w i n g i r r a d i a t i o n to 1.6 x 1017e/ca 2. The e x t e n t o f the i r r a d i a e i o n s o f t e n i n g i s not as g r e a t , but i s s t i l l d e c r e a s e in the y i e l d s t r e s s v i a i r r a d i a t i o n to 1.6 x 1017e/cm 2, an i n c r e a s e in s t r a i n r a t e by a f a c t o r o f 10 caused l i t t l e The change was always l e s s than 0.5% o f the flow s t r e s s .
significant;
30%
In a l l c i r c u m s l a n c e s ,
change in the flow s t r e s s . When t e n s i l e t e s t s were
i n t e r r u p t e d , s t r e s s r e l a x a t i o n was v e r y s m a l l . The nagnitude o f observed e f f e c t s are s u r p r i s i n g l y l a r g e in view o f e l e c t r o n doses employed.
When t h e displacement t h r e s h o l d energy i s assumed to be 20 eV, d i s -
placement cro s s s e c t i o n i s 150 x 10"24c~ 2, 60% o f which r e s u l t s in s i n g l e p o i n t d e f e c t s (4).
Thus, the c o n c e n t r a t i o n o f p o i n t d e f e c t s i s between 5 x 10 -6 and 2 x 10 -5 f o r the
e l e c t r o n doses used h e r e .
I f we f u r S h e r assume t h a t the replacement energy i s o f the
o r d e r of 1 eV, t h e number o f replacements i s s i x times t h a t o f the displacement (5). Considering t h a t ,
in an a v e r a g e , e i g h t bonds are d i s o r d e r e d per r e p l a c e m e n t , i r r a d i a t i o n
induced change in long range o r d e r parameter, S , can be expected to be o f the o r d e r 10 "3.
of
D i s o r d e r i n g i n c r e a s e s th e y i e l d s t r e s s o f some ordered a l l o y s a t low temperatures (6).
However, the magnitude o f $ o f annealed NiSA1 i s about 0.9 (7) and the small change
in $ as p r e d i c t e d f o r the p r e s e n t i r r a d i a t i o n cannot p o s s i b l y e x p l a i n s u b s t a n t i a l changes in the y i e l d s t r e s s o f i r r a d i a t e d NisA1.
Observed i r r a d i a t i o n hardening appears to be
due to the presence o f p o i n t d e f e c t s a n d / o r t h e i r c l u s t e r s .
However, t h e usual d i s p e r s e d
b a r r i e r mechanism cannot be invoked in the absence o f s i g u i f i c a n t s t r a i n r a t e dependence o f the y i e l d s t r e s s still
(8,9).
unknown manner.
understanding.
Point d e f e c t s may c o n t r i b u t e to l a t t i c e
f r i c t i o n s t r e s s in a
C l e a r l y , more e x t e n s i v e study o f t h i s e f f e c t must be made f o r f u l l
Vol. 2, No. 6
IRRADIATION
In the case of the irradiation clusters
are unlikely
very sensitive
SOFTENING
AA'I) H A K D E N L N G
softening
a t 500°K, p o i n t d e f e c t s
t o be a c a u s e o f t h e s o f t e n i n g .
t o t h e s m a l l change i n S, so t h a t
cannot explain the softening.
One p o s s i b l e
Again t h e y i e l d
slight
disordering
contribute alloy
and r e p l a c e m e n t c o l l i s i o n s .
to a dislocation
(11) r e d u c t i o n
drag just
in either
(I0),
NisAl
333
and t h e i r stress
is not
due t o i r r a d i a t i o n
mechanism o f t h e s o f t e n i n g
d o m a i n s " , which h a v e b e e n s u g g e s t e d by a c o m p u t e r e x p e r i m e n t process of displacement
OF
is that
"micro-
are destroyed
in the
Since the micro-domains should
as do G u i n i e r - P r e s t o n
zones i n an a g e - h a r d e n e d
t h e number o r t h e e f f e c t i v e n e s s
of the micro-domains will reduce the yield stress.
as a d i s l o c a t i o n
drag
This softening mechanism is valid
in other partially ordered alloys, so that a similar softening should be observed via further
investigation
using other alloy systems.
References i.
R. G. Davies and N.S. S t o l o f f , Trans. TMS-AI~ 235, 714 (1965).
2.
S. M. Copley and B.H. Kear, Trans. TMS-AI~
5.
A. C. Damask, Studies in Radiation Effects on Solids, Vol. 2, p. 1, Gordon and B r e a c h , New York ( 1 9 6 7 ) .
4.
G. H. Kinchin and R.S. Pease, J. Nucl. Energy I, 200 (1955).
5.
G. J. Dienes and G.H. Vineyard, Radiation Effects in Solids, p. 32 . Interscience, New York (1957).
6.
N. S. Stoloff and R. G. Davies, Progress in Materials Pergamon Press, New York (1966).
7.
C. L. Corey and D. I. Potter, J. Appl. Phys. 58, 5894 (1967).
8.
A. Seeger, Proc. 2nd Int. Conf. PUAE, 6, p.250, United Nations, New York (1958).
9.
K. Ono and M. Meshii, Trans. ASM 60, 426 (1967).
259, 977 (1967).
Sci., Vol. 15, p. 43,
I0. P.C. Gehlen and J. B. Cohen, Phys. Rev. 159, A844 (1965). II. R. W. Cahn, Local Atomic Arrangements Studied by X-ray Diffraction, p. 196. Gordon and Breach, New York (1966).