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CORRELATION BETWEEN THE MICROSCOPIC DISTRIBUTION OF RADIATION-INDUCED FREE VOLUME AND THE DUCTILITY OF AMORPHOUS
ALLOYS
R. Gerling, F. Schimansky, R. Wagner
To cite this version:
R. Gerling, F. Schimansky, R. Wagner. CORRELATION BETWEEN THE MICROSCOPIC DISTRIBUTION OF RADIATION-INDUCED FREE VOLUME AND THE DUCTILITY OF AMORPHOUS ALLOYS. Journal de Physique Colloques, 1985, 46 (C8), pp.C8-539-C8-543.
�10.1051/jphyscol:1985885�. �jpa-00225238�
JOURNAL DE PHYSIQUE
Colloque C8, supplément au n°12, Tome 46, décembre 1985 page C8-539
CORRELATION BETWEEN THE MICROSCOPIC DISTRIBUTION OF RADIATION-INDUCED FREE VOLUME AND THE DUCTILITY OF AMORPHOUS ALLOYS
R. G e r l i n g , F . P . Schimansky and R. Wagner
GKSS-Forschungszentrum, P.O. Box 1160, D-2054 Geesthacht, F.R.G.
Résumé - L'irradiation aux neutrons d'alliages amorphes fragilisés thermiquement produit une augmentation macroscopique du volume et une réapparition de la duc- tilité. Ces effets ont été étudiés en fonction du type d'irradiation : neutrons rapides et particules a et Li produites par les neutrons thermiques. Le gonfle- ment total ne dépend pas du type d'irradiation mais seulement de la dose. Ce- pendant, le niveau d'irradiation nécessaire à la réapparition complète de la ductilité dépend du type de particules. Ceci est attribué au fait que le vo- lume libre résultant des irradiations est distribué de manières très diffé- rentes dans le matériau.
A b s t r a c t - N e u t r o n - i r r a d i a t i o n of t h e r m a l l y e m b r i t t l e d F e4 0N i4 0P2 0 and F e4 0N i4 0B2 0 amorphous a l l o y s l e a d s t o a m a c r o s c o p i c s w e l l i n g which e f f e c t s a c o m p l e t e r e c o v e r y of t h e d u c t i l i t y . Both t h e i r r a d i a t i o n - i n d u c e d s w e l l i n g and t h e a s s o c i a t e d improvement of t h e d u c t i l i t y have been s t u d i e d a s a f u n c t i o n of two t y p e s of damaging p r o j e c t i l e s : f a s t n e u t r o n s , and a - and L i - p a r t i c l e s g e n e r a t e d by t h e r m a l n e u t r o n s . The t o t a l amount of s w e l l i n g i s i n d e p e n d e n t of t h e t y p e of damaging s p e c i e s and o n l y depends on t h e damage l e v e l . However, t h e damage l e v e l r e q u i r e d f o r c o m p l e t e r e s t o r a t i o n of t h e d u c t i l i t y depends s t r o n g l y on t h e t y p e of damaging p r o j e c t i l e s . This i s a consequence of l a r g e d i f f e r e n c e s i n t h e d i s t r i b u t i o n of i r r a d i a t i o n - i n d u c e d f r e e volume w i t h r e - s p e c t t o t h e two d i f f e r e n t damaging modes.
I - INTRODUCTION
Some r e c e n t e x p e r i m e n t s y i e l d e d an improved d u c t i l i t y of amorphous a l l o y s a f t e r n e u - t r o n - i r r a d i a t i o n . Kayano e t a l . /1 / r e p o r t e d an i n c r e a s e d d u c t i l i t y a f t e r n - i r r a d i a - t i o n of a s - q u e n c h e d P dB 0S i2 0. Kramer e t a l . /2/ found t h e { H o0,6R u0. Je 2B i e a l l o y t o be c o m p l e t e l y d u c t i l e a f t e r n - i r r a d i a t i o n , w h i l e t h e a s - q u e n c h e d a l l o y had been b r i t t l e . I n p r e v i o u s p a p e r s / 3 , 1 / we r e p o r t e d t h a t even t h e r m a l l y e m b r i t t l e d amor- phous Fem,Nim,B2 0 became d u c t i l e a f t e r l o w - d o s e n - i r r a d i a t i o n . S i m i l a r r e s u l t s have l a t e r been r e p o r t e d on t h e r m a l l y e m b r i t t l e d F eH 0N i ^0P , ^ Bs / 5 / .
I t h a s been e s t a b l i s h e d t h a t t h e e m b r i t t l e m e n t of F e ^ N i ^ B j , a t a n n e a l i n g t e m p e r a - t u r e s f a r below t h e c r y s t a l l i z a t i o n t e m p e r a t u r e i s a s s o c i a t e d w i t h a s l i g h t i n c r e a s e of t h e d e n s i t y by - 0 . 1 %, w h i l e t h e c o m p l e t e r e s t o r a t i o n of t h e d u c t i l i t y d u r i n g n - i r r a d i a t i o n i s c o r r e l a t e d w i t h a d e c r e a s e of t h e d e n s i t y / * ) / . Thus, we c o n c l u d e d t h a t t h e f r e e volume i s e s s e n t i a l for d u c t i l e b e h a v i o u r and i t i s t h e i r r a d i a t i o n - induced s w e l l i n g which r e n d e r s t h e s p e c i m e n s d u c t i l e a g a i n / I , 6 / .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985885
C8-540 J O U R N A L
DE
PHYSIQUEI t r e m a i n s open, however, a s t o whether i t is o n l y t h e t o t a l amount o f i r r a d i a t i o n - induced m i c r o s c o p i c free volume o r r a t h e r its s p e c i f i c d i s t r i b u t i o n which promotes d u c t i l e b e h a v i o u r . To s t u d y a c o n c e i v a b l e i n f l u e n c e o f t h e m i c r o s c o p i c d i s t r i b u t i o n o f f r e e volume o n t h e d u c t i l i t y , amorphous Fe,,Ni,,B2, a n d Fe,,Ni,,P2, a l l o y s a r e exposed t o two d i f f e r e n t t y p e s o f r a d i a t i o n damage.
I1
-
EXPERIMENTALT h r e e d i f f e r e n t r i b b o n s of amorphous a l l o y s have been p r e p a r e d by t h e Vacuum Schmelze Hanau, FRG: Fe,,Ni,,P2, ( 2 5 um t h i c k , 10 mm w i d e ) ; Fe,,Ni,,'oB2, ( l 0 B en- r i c h m e n t 86 % ; 40
u m
t h i c k , 3 mm w i d e ) ; Fe,,Ni,,11B2, ("B e n r i c h m e n t 99.2 %; 40 urn t h i c k , 3 mm w i d e ) .The r e l a t i v e s t r a i n a t f r a c t u r e , c f , a s d e t e r m i n e d from b e n d i n g t e s t s /7/ is t a k e n a s a m e a s u r e o f t h e d u c t i l i t y o f t h e r e s p e c t i v e s p e c i m e n . The d e n s i t y was e v a l u a t e d by w e i g h i n g t h e s p e c i m e n s b o t h i n a i r and t e t r a b r o m o e t h a n e . N e u t r o n - i r r a d a t i o n was performed i n an i n - c o r e r e a c t o r p o s i t i o n .
I n o r d e r t o a l l o w u s t o s t u d y a n improvement o f t h e d u c t i l i t y d u r i n g n - i r r a d i a t i o n . t h e s p e c i m e n s w e r e t h e r m a l l y e m b r i t t l e d p r i o r t o t h e i r r a d i a t i o n . F i g . 1 shows c f . a f t e r i s o c h r o n a l a n n e a l i n g ( 4 3 h under h i g h vacuum) o f t h e t h r e e d i f f e r e n t r i b b o n s . The e m b r i t t l e m e n t c u r v e s a r e each c h a r a c t e r i z e d by a s t e p - l i k e b e h a v i o u r : F u l l y d u c t i l e s p e c i m e n s ( E ~ = 1 ) e x p e r i e n c e a d r a s t i c l o s s o f d u c t i l i t y ( c f
<
1 ) a t l o w e r t e m p e r a t u r e s f o l l o w e d by a m o r e o r l e s s pronounced p l a t e a u ( E ~-
2 a n d as e c o n d d e c r e a s e o f c f a t t h e end o f which t h e s p e c i m e n s were found t o have c r y s t a l - l i z e d . The f i r s t l o s s o f d u c t i l i t y i s always a s s o c i a t e d w i t h a s l i g h t i n c r e a s e ( - 0 . 1 % ) o f t h e d e n s i t y /4/. Thus, t h e a n n e a l i n g t e m p e r a t u r e (TA) f o r each r i b b o n was chosen s u c h t h a t t h e e m b r i t t l e m e n t o f e a c h r i b b o n was o n l y due t o t h e l o s s o f f r e e volume: TA(Fe,,Ni,,P,,) = 250 O C , TA(Fe,,Ni,,10B2,) = 280 OC, TA(Fe,,Ni,,"B,,)
= 304 OC. I t was c o n f i r m e d by DSC and TEM t h a t t h e s p e c i m e n s remained c o m p l e t e l y amorphous a f t e r t h e p a r t i c u l a r h e a t t r e a t m e n t a t TA.
k l l l l l l l l l l .
as 200 2L0 280 320 360
q U Temperature I°C
F i g . 1
-
T h e t e m p e r a t u r e d e - pendence o f t h e r e l a t i v e s t r a i n a t f r a c t u r e f o r t h r e e d i f f e r e n t r i b b o n s.
D u r i n g t h e i n - c o r e i r r a d i a t i o n , t h e s p e c i m e n s were s i m u l t a n e o u s l y e x p o s e d t o f l u x e s o f @ t h = 3 . 5 l o a 3 n / c m 2 s e c (En
<
0.1 eV) a n d qf = 2.2 l o t 3 n/cm2sec (En>
0.1 MeV) o f t h e r m a l and f a s t n e u t r o n s , r e s p e c t i v e l y . The t o t a l damage o f a FeNiB-alloy c o n s i s t s of two d i f f e r e n t c o n t r i b u t i o n s :-
i ) d i s p l a c e m e n t s due t o f a s t n e u t r o n s ; - ii ) d i s p l a c e m e n t s g e n e r a t e d by h i g h - e n e r g y a - and L i - p a r t i c l e s r e s u l t i n g from t h e c a p t u r e o f t h e r m a l n e u t r o n s by "'B.h he
l a t t e r t y p e o f i r r a d i a t i o n c o r r e s p o n d s , i n f a c t , t o a l i g h t - i o n bombardment. However, i n c o n t r a s t t o c o n v e n t i o n a l l i g h t - i o n i r r a d i a t i o n , i n t h e p r e s e n t c a s e t h e damage is homogeneous t h r o u g h o u t t h e whole s p e c i m e n , b e c a u s e t h e a- and L i - p a r t i c l e s a r e g e n e r a t e d homogeneously w i t h i n t h e s p e c i m e n . ] Damage c a l c u l a t i o n s which c o n s i d e r t h e s p e c i f i c n e u t r o n e n e r g y s p e c t r u m a t t h e c h o s e n i n - c o r e p o s i t i o n have shown /8/ t h a t a f t e r a g i v e n i r r a d i a t i o n t i m e t h e damage l e v e l ( e x p r e s s e d i n terms of d i s p l a c e m e n t s p e r , a t o m -dpa-) c a u s e d by e i t h e r f a s t n e u t r o n s o r by a- and L i - p a r t i c l e s is d i f f e r e n t f o r t h e t h r e e d i f f e r e n tg l a s s y a l l o y s . For each a l l o y . T a b l e 1 shows t h e c o n t r i b u t i o n s from f a s t n e u t r o n s (dpaf ) and from h i g h e n e r g y or- and L i - p a r t i c l e s (dpa, Li) t o t h e t o t a l d i s p l a c e m e n t l e v e l o f 1 d p a . While i n F e , , N i , , l ~ B , , t h e damage is g e n e r a t e d e s s e n t i a l l y by a- and L i - p a r t i c l e s , i n Fe,,Ni,,P,, t h e r a d i a t i o n damage is caused e x c l u s i v e l y by t h e f a s t n e u t r o n s . I n Fe,,Ni,,11B2,, t h e r e m a i n i n g 'OB i m p u r i t y o f 0.16 a t % i s s t i l l s u f f i - c i e n t f o r t h e damage by a - and L i - p a r t i c l e s t o d o m i n a t e . However, C d - s h i e l d i n g o f t h i s a l l o y s u p p r e s s e s t h e t h e r m a l n e u t r o n f l u x t o s u c h a d e g r e e t h a t t h e damage by f a s t n e u t r o n s now p r e v a i l s .
Thus, t h e u s e o f t h e s e t h r e e amorphous a l l o y s a l l o w s u s n o t o n l y t o v a r y t h e damag- i n g mode f o r one s i n g l e a l l o y (Fe,,Ni,,llB,,) by means o f an o p t i o n a l C d - s h i e l d i n g , b u t a l s o t o s t u d y t h e e x c l u s i v e i n f l u e n c e o f each o f t h e two t y p e s o f damaging modes on e i t h e r Fe,,Ni,,lOB,, ( d ~ a , , ~ ~ = 1 ) o r Fe,,Ni,,P,, (dpaf = I ) , which a r e supposed t o be two r a t h e r s i m i l a r amorphous a l l o y s .
T a b l e 1 - The c o n t r i b u t i o n s of t h e two t y p e s of r a d i a t i o n damage t o t h e t o t a l damage o f 1 d p a . d p a o r l L i d e n o t e s t h e c o n t r i b u t i o n o f t h e r m a l n e u t r o n - i n d u c e d a - a n d Li-damage, w h i l e dpaf r e f e r s t o t h e c o n t r i b u t i o n s o f damage by f a s t n e u t r o n s . (Cd) r e f e r s t o an i r r a d i a t i o n b e h i n d a C d - s h i e l d i n g .
I11 - RESULTS AND DISCUSSION
I n F i g . 2 t h e d e n s i t y i s p l o t t e d v e r s u s t h e d p a - l e v e l f o r one FeNiP and a v a r i e t y o f FeNiB a l l o y s . For a l l s p e c i m e n s a m a c r o s c o p i c s w e l l i n g is o b s e r v e d a f t e r i r r a d i a - t i o n . Moreover, i r r e s p e c t i v e o f t h e d o m i n a t i n g damaging mode, a t a g i v e n ( t o t a l ) dpa- l e v e l , a l l specimens e x h i b i t t h e same amount of s w e l l i n g .
The dependence o f t h e r e l a t i v e s t r a i n a t f r a c t u r e o n t h e damage l e v e l is shown i n F i g . 3. Common t o a l l a l l o y s is t h e complete r e s t o r a t i o n o f t h e d u c t i l i t y a l t h o u g h t h e d p a - l e v e l a t w h i c h E~ = 1 is r e g a i n e d i s c o m p l e t e l y d i f f e r e n t f o r t h e v a r i o u s a l l o y s . S i n c e t h e l o s s o f d u c t i l i t y d u r i n g t h e r m a l a n n e a l i n g ( e . g . F i g . 1 ) i s a con- s e q u e n c e o f t h e i n c r e a s e o f t h e d e n s i t y , t h e i r r a d i a t i o n - i n d u c e d s w e l l i n g was con- c l u d e d / 4 , 6 / t o be r e s p o n s i b l e f o r t h e r e - d u c t i l i s a t i o n d u r i n g i r r a d i a t i o n . How- e v e r , a s t h e a l l o y s have r e c o v e r e d a f t e r i r r a d i a t i o n t o d i f f e r e n t amounts o f swel- l i n g , e . g . Fe,,Ni,,"B,, (Cd) r e c o v e r e d a l r e a d y a f t e r s w e l l i n g o f
-
0.1 % w h e r e a s t h e "B-alloy r e q u i r e s s w e l l i n g o f 0.3 % ( F i g . 2 ) , i t is n o t o n l y t h e t o t a l amount o f f r e e volume g e n e r a t e d d u r i n g i r r a d i a t i o n which c o n t r o l s t h e b r i t t l e - d u c t i l e t r a n - s i t i o n b u t a l s o t h e way how i t is d i s t r i b u t e d w i t h i n t h e amorphous s t r u c t u r e . The r e s t o r a t i o n o f t h e d u c t i l i t y o f t h e "B-alloy s u g g e s t s a n i n f l u e n c e o f t h e dam- a g i n g mode: While t h e d u c t i l i t y o f C d - s h i e l d e d Fe,,Ni,,"B2, ( t h e d o m i n a t i n g damage is caused by f a s t n e u t r o n s ) is r e s t o r e d a t about-
1 lo-' d p a , u n s h i e l d e d i r r a d i a -$0996
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10-2D~splacements per Atom
F i g . 2 - The v a r i a t i o n o f t h e r e l a t i v e d e n s i t y a f t e r n - i r r a d i a t i o n w i t h t h e damage l e v e l f o r one FeNiP and a v a r i e t y of FeNiB a l l o y s . (Cd) r e - f e r s t o an i r r a d i a t i o n b e h i n d a C d - s h i e l d i n g .
C8-542 JOURNAL
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A S o FeLo NI, "B,t i o n of t h i s a l l o y ( t h e dominating damage t h e n r e s u l t s from a - and L i - p a r t i c l e s ) y i e l d s d u c t i l e behaviour o n l y beyond
-
3.
lo-'' dpa. A s i m i l a r t e n d e n c y , though even more pronounced, is observed f o r Fe,,Ni,,P,, and Fe,oNi,o'oB,o. Fe,,Ni,,P,,, which i s damaged e x c l u s i v e l y by f a s t n e u t r o n s , a l s o becomes d u c t i l e a t a b o u t-
1.
lo-'d p a , whereas t h e "B-alloy which i s damaged by a - and L i - i o n s e v e n t u a l l y becomes d u c t i l e a t 2 dpa. These r e s u l t s s u g g e s t t h a t t h e damage by f a s t n e u t r o n s is w i t h r e s p e c t t o t h e r e s t o r a t i o n o f t h e d u c t i l i t y f a r more e f f i c i e n t t h a n t h e damage by a - and L i - p a r t i c l e s .
o f t h e r e l a t i v e s t r a i n a t f r a c t u r e h f t e r neu- t r o n - i r r a d i a t i o n w i t h t h e damage l e v e l f o r t h r e e d i f f e r e n t r i b - bons. (Cd) r e f e r s t o an i r r a d i a t i o n behind a C d - s h i e l d i n g o f t h e p a r t i c u l a r a l l o y .
B e f o r e we d i s c u s s d i f f e r e n c e s between t h e damaging p r o c e s s e s by f a s t n e u t r o n s and by a - and L i - p a r t i c l e s , we must f i r s t e s t a b l i s h t h a t t h e d i f f e r e n t d p a - l e v e l s f o r com- p l e t e r e s t o r a t i o n o f t h e d u c t i l i t y do n o t a r i s e from:
- i ) t h e d i f f e r e n t a n n e a l i n g t e m p e r a t u r e s p r i o r t o t h e i r r a d i a t i o n . - i i ) t h e e f f e c t of damage r a t e ,
- i i i ) t h e p r o d u c t i o n of ' g a s e o u s ' He and L i due t o t h e burn-up of ' O B /7/.
i ) T h i s e f f e c t can be excluded f o r Fe,,Ni,,''B,, s i n c e a s i n g l e a l l o y h a s been ex- posed t o d i f f e r e n t t y p e s of i r r a d i a t i o n . Indeed Fe,oNi,o'OB,o was a n n e a l e d a t a s l i g h t l y h i g h e r t e m p e r a t u r e t h a n Fe,oNi,oP,o
,
b o t h t e m p e r a t u r e s , however, a r e w e l l below t h e a n n e a l i n g t e m p e r a t u r e used f o r t h e "B-alloy. Thus, any c o n c e i v a b l e em- b r i t t l i n g e f f e c t o t h e r t h a n t h e l o s s of f r e e volume s h o u l d have been most pronounced f o r Fe,,Ni,,"B,,. S i n c e t h i s a l l o y r e c o v e r e d a t t h e l o w e s t damage l e v e l an e f f e c t of t h e d i f f e r e n t a n n e a l i n g t e m p e r a t u r e s can be r u l e d o u t .i i ) The damage r a t e a f f e c t s t h e d e f e c t s t r u c t u r e i f t h e r a d i a t i o n damage can p a r t l y r e c o v e r d u r i n g t h e i r r a d i a t i o n . A r a t e e f f e c t would r e q u i r e a h i g h e r dpa-level t o r e v e a l a complete r e s t o r a t i o n o f t h e d u c t i l i t y t h e s m a l l e r t h e damage r a t e is. How- e v e r , s i n c e i n t h i s c a s e t h e damage r a t e i n c r e a s e s from Fe,,Ni,,P,, o f 2
-
lo-'d p a / s e c v i a F e , o N i , o l l ~ , o t o 1.1
.
lo-' d p a / s e c f o r t h a t of Fe,oNi,o'OB,o, and be- c a u s e t h e l a t t e r a l l o y r e c o v e r e d a t t h e h i g h e s t d p a - l e v e l , a r a t e e f f e c t can a l s o be e x c l u d e d .i i i ) Due t o t h e burn-up o f 'OB, a - and L i - p a r t i c l e s a r e g e n e r a t e d and remain
-
t o a c e r t a i n e x t e n t-
w i t h i n t h e specimens. T h i s c o u l d p o s s i b l y impede t h e r e s t o r a t i o n of t h e d u c t i l i t y . TEM i n v e s t i g a t i o n s of n - i r r a d i a t e d Fe,oNi,o'oB,o r e v e a l e d s m a l l He b u b b l e s o n l y when t h e t o t a l amount of He g e n e r a t e d d u r i n g i r r a d i a t i o n exceeded 1.3 a t $ / 9 / . I n t h i s c a s e , t h e concomitant l o s s of d u c t i l i t y can be a t t r i b u t e d t o t h e e m b r i t t l i n g i n f l u e n c e o f He. During t h e p r e s e n t i r r a d i a t i o n e x p e r i m e n t s , however, t h e l e v e l of He g e n e r a t e d i n F e , o N i , o ' O ~ , o a t t h e d p a - l e v e l of complete r e c o v e r y i s o n l y 4.6 a t $ ; He s h o u l d t h e r e f o r e have no i n f l u e n c e on t h e d u c t i l i t y .The r e s t o r a t i o n o f t h e d u c t i l i t y a t d i f f e r e n t d p a - l e v e l s is e v i d e n t l y r e l a t e d t o t h e d i f f e r e n t damaging modes. The f a c t , t h a t t h e t o t a l amount of f r e e volume i n t r o d u c e d d u r i n g i r r r a d i a t i o n t o t h e same damage l e v e l is a b o u t t h e same f o r a l l specimens ( F i g . 2) s u g g e s t s t h a t t h e m i c r o s c o p i c d i s t r i b u t i o n of t h e i r r a d i a t i o n induced f r e e volume c o n t r o l s t h e b r i t t l e - t o - d u c t i l e t r a n s i t i o n .
T a b l e 2
-
The p r o b a b i l i t i e s o f c a s c a d e s w i t h a c e r t a i n number o f d i s p l a c e d a t o m s . The p r o b a b i l i t i e s a r e l i s t e d s e p a r a t e l y f o r a- and Li-damage and f o r f a s t n e u t r o n damage.Cascade slze [displaced
atoms1 1 - 10 10 - 5 0 50 - 100
> 100
S i n c e t h e damage c a s c a d e s a r e t h e s o u r c e s o f r a d i a t i o n - i n d u c e d f r e e volume, d i f f e r - e n c e s i n t h e m i c r o s c o p i c d i s t r i b u t i o n o f f r e e volume can o n l y be e x p e c t e d i f t h e damage c a s c a d e s g e n e r a t e d by t h e two damaging modes a r e d i f f e r e n t . D e t a i l e d c a l c u l a - t i o n s / 8 / o f t h e damaging p r o c e s s e s r e v e a l e d l a r g e d i f f e r e n c e s w i t h r e s p e c t t o t h e c a s c a d e s i z e d i s t r i b u t i o n ( T a b . 2 ) . While d u r i n g t h e damage by a - and L i - p a r t i c l e s n e a r l y a l l c a s c a d e s i n v o l v e o n l y 1 t o 10 a t o m s , more t h a n 75 % o f t h e c a s c a d e s gene- r a t e d by f a s t n e u t r o n s c o n t a i n more t h a n 10 atoms and 38 % o f a l l c a s c a d e s c o n t a i n even more t h a n 100 atoms. I n a - and Li-damaged a l l o y s which c o n t a i n a g r e a t number o f v e r y s m a l l c a s c a d e s , t h e e x c e s s volume i s t h e r e f o r e d i s t r i b u t e d n e a r l y homoge- n e o u s l y i n v e r y s m a l l u n i t s t h r o u g h o u t t h e specimen, w h i l e i n f a s t neutron-damaged a l l o y s t h e f r e e volume is c o n t a i n e d i n r a t h e r l a r g e u n i t s b u t w i t h a s m a l l e r number d e n s i t y . The l a t t e r d i s t r i b u t i o n seems t o f a v o u r t h e b r i t t l e - d u c t i l e t r a n s i t i o n . I V - CONCLUSION
Damage induced by a- and Li - particles
[ % I
9 7 . 8 1.9 0.2 0.1
From t h e p r e s e n t r e s u l t s t h e f o l l o w i n g c o n c l u s i o n s can be drawn, t h e v a l i d i t y o f which is n o t c o n f i n e d t o i r r a d i a t i o n e x p e r i m e n t s :
Fast neutron induced damage
[ % I
2 L.9 19.9 16.7 3 8.5
i ) Excess f r e e volume is e s s e n t i a l f o r d u c t i l e b e h a v i o u r o f amorphous a l l o y s . i i ) T o p o l o g i c a l l y d i f f e r e n t f r e e volume s i t e s a r e s t a b l e w i t h i n t h e amorphous
s t r u c t u r e .
i i i ) To a c e r t a i n e x t e n t i t i s t h e m i c r o s c o p i c d i s t r i b u t i o n o f f r e e volume r a t h e r t h a n t h e t o t a l amount, which f a v o u r s d u c t i l e b e h a v i o u r : F r e e volume b e i n g s p r e a d homogeneously t h r o u g h o u t t h e specimen is l e s s b e n e f i c i a l f o r d u c t i l e b e h a v i o u r t h a n f r e e volume b e i n g r a t h e r c o n c e n t r a t e d w i t h i n some few b u t more e x t e n d e d r e g i o n s .
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