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Surface segregation measurements duringelectron irradiationT. Muroga a b , P. R. Okamoto a & H. Wiedersich aa Materials Science and Technology Division, Argonne NationalLaboratory , Argonne , Illb Department of Nuclear Engineering , University of Tokyo , Tokyo ,JapanPublished online: 19 Aug 2006.

To cite this article: T. Muroga , P. R. Okamoto & H. Wiedersich (1983) Surface segregation measurementsduring electron irradiation, Radiation Effects, 68:6, 163-167, DOI: 10.1080/01422448308226436

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Radiation Effects Letters, 1983, Vol. 68, pp. 163-167

01983, Gordon and Breach, Science Publishers, Inc. Printed in t he United States of America

0 142-244 8/83/6806-O 163 $18.5 O/O

SURFACE SEGREGATION MEASUREMENTS D U R I N G ELECTRON IRRADIATION

T . MUROGA', P .R . OKAMOTO and H . WIEDERSICH Materials Sc ience and Technology D i v i s i o n , Argonne Na t iona l Labora to ry , Argonne, I l l . + U n i v e r s i t y o f Tokyo, Tokyo, Japan .

P r e s e n t a d d r e s s ; Department o f Nuclear Eng inee r ing ,

(Received for Publication December 10, 1982)

The growth o f Ni3Si s u r f a c e f i l m s on Ni-12.7at%Si a l l o y s h a s been measured d u r i n g l M e V e l e c t r o n i r r a d i a t i o n . S t e r e o s c o p i c tech- n iques w e r e used t o de te rmine f i l m t h i c k n e s s from da rk f i e l d images formed from Ni3Si s u p e r l a t t i c e r e f l e c t i o n s . P a r a b o l i c growth k i n e t i c s are observed a t lower t empera tu res . However, a t h i g h e r t empera tu res , d e v i a t i o n s from p a r a b o l i c k i n e t i c s are observed a f t e r s h o r t i r r a d i a t i o n t i m e s . Such d e v i a t i o n s have n o t been observed i n bu lk specimens d u r i n g bombardment w i t h e n e r g e t i c i o n s and , t h e r e f o r e , may b e due t o f o i l t h i c k n e s s e f f e c t s .

INTRODUCTION

Radia t ion- induced s u r f a c e s e g r e g a t i o n i s commonly found i n many a l l o y s . I n Ni-Si a l l o y , p r e v i o u s i n v e s t i g a t i o n s have shown t h a t c o h e r e n t f i l m s of t h e o r d e r e d i n t e r m e t a l i c phase , Ni3Si , form and grow on t h e s u r f a c e d u r i n g i o n i r r a d i a t i o n as a r e s u l t o f t h e p r e f e r e n t i a l t r a n s p o r t of S i t o t h e s u r f a c e by d e f e c t f l u x e s [ l l .

I n t h i s s t u d y , d i r e c t o b s e r v a t i o n s o f t h e fo rma t ion o f Ni3Si f i l m s on N i - 1 2 . 7 a t % S i a l l o y s and measurements o f t h e i r growth rates d u r i n g e l e c t r o n i r r a d i a t i o n i s r e p o r t e d . Th i s work has provided i n f o r m a t i o n n o t o n l y abou t t h e m i c r o s t r u c t u r a l changes which occur d u r i n g r a d i a t i o n enhanced s e g r e g a t i o n b u t a l so a b o u t some impor t an t c h a r a c t e r i s t i c s of t h e e l c t r o n damage a s a t echn ique f o r s i m u l a t i n g f u s i o n neu t ron i r r a d i a t i o n s .

EXPERIMENTAL

Specimens of N i - 1 2 . 7 a t % S i i n t h e form of 3mm d i s c s w e r e punched from c o l d r o l l e d f o i l s . The d i s c s w e r e annea led a t 95OOC f o r 6 hour s i n a q u a r t z tube b a c k - f i l l e d w i t h h igh p u r i t y a rgon and subsequen t ly water quenched. Transmiss ion e l e c t r o n microscopy examinat ion o f as- quenched samples showed no ev idence of any Ni3Si p r e c i p i t a t e s .

v o l t a g e e l e c t r o n microscope a t ANL. Though some o b s e r v a t i o n s were I r r a d i a t i o n s w e r e performed w i t h l M e V e l e c t r o n s u s i n g t h e h igh

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c a r r i e d o u t i n - s i t u i n t h e HVEM, more d e t a i l e d m i c r o s t r u c t u r a l exami- n a t i o n s were performed u s i n g JEM-100CX a f t e r i r r a d i a t i o n .

I n c a l c u l a t i n g t h e d i sp lacemen t dose, McKinley-Feshbach's formula[2] w a s used w i t h t h e d i sp lacemen t t h r e s h o l d energy of 33eV. I n t h e s e expe r imen t s , t h e d i sp lacemen t r a t e w a s 5x10'4 d i sp lacemen t p e r a t o m p e r second (dpa / sec ) a t t h e c e n t e r o f t h e beam. The sample t h i c k n e s s w a s between 200nm and 250nm.

RESULTS AND DISCUSSION

A f t e r some i r r a d i a t i o n a t e l e v a t e d t empera tu re (40O-65O0C), Ni3Si s u p e r l a t t i c e r e f l e c t i o n s appea r i n t h e d i f f r a c t i o n p a t t e r n s . F i g u r e 1 shows a dark f i e l d image o f t h e s u r f a c e f i l m t a k e n w i t h a s u p e r l a t t i c e r e f l e c t i o n . Domain boundar i e s o f t h e s u r f a c e f i l m are observed i n i r r a d i a t e d area. The h i g h d e n s i t y of s m a l l d e s c r e t e p a r t i c l e s observed i n u n - i r r a d i a t e d area are t h e r m a l l y formed Ni3Si p r e c i p i t a t e s .

F i g u r e 2 shows i n t e r s t i t i a l l o o p s i n a sample i r r a d i a t e d a t a r e l a t i v e l y l o w t empera tu re . Pa r t i c l e d e p l e t e d zones are c l e a r l y observed i n t h e v i c i n i t y of d i s l o c a t i o n l o o p s . T h i s shows t h a t d i s - l o c a t i o n s are s o l u t e s i n k s .

F i g u r e s 3-a and 3-b are t h e stereo p a i r s o f t h e same domain s t r u c t u r e i n t h e s u r f a c e f i l m . Such stereo p a i r s w e r e used to deter- mine t h e t h i c k n e s s e s of t h e f i l m s .

F i g u r e 4 shows t h e f i l m t h i c k n e s s e s a t l o w t empera tu res as a f u n c t i o n of t h e s q u a r e roo t o f t h e dose . The p a r a b o l i c growth k i n e t - ics i n d i c a t e t h a t f i l m growth i s d i f f u s i o n c o n t r o l l e d i n agreement w i t h t h o s e d e r i v e d w i t h i o n i r r a d i a t i o n s 1 3 1 . F i g u r e 5 i s an Arrhenius p l o t of t h e measured growth ra te c o n s t a n t s . According t o t h e f i l m growth model by Okamoto e t a 1 . [ 4 1 , growth r a t e c o n s t a n t i n t h i s t e m - p e r a t u r e r e g i o n i s p r o p o r t i o n a l to (Dv/K,)1/4, where Dv i s t h e vacancy d i f f u s i o n c o e f f i c i e n t and K O i s t h e d e f e c t p r o d u c t i o n ra te . Using t h i s r e l a t i o n , a m i g r a t i o n energy o f vacancy of l . l e V can be deduced from t h e s l o p e i n F i g u r e 5 . T h i s v a l u e i s i n good cor respondence w i t h v a l u e s d e r i v e d by i o n i r r a d i a t i o n s I 4 1 .

F i g u r e 6 shows t h e f i l m t h i c k n e s s e s a t h i g h e r t empera tu res as a f u n c t i o n o f t h e s q u a r e root o f t h e dose . I n c o n t r a s t t o F i g u r e 4 , obvious dev ia t ions from p a r a b o l i c growth k i n e t i c s are obse rved . Such d e v i a t i o n s a r e b e l i e v e d t o b e r e l a t e d t o a "Soft-impingment" e f f e c t which o c c u r s when t h e s u b s u r f a c e S i d e p l e t e d zones which accompany f i l m growth become s u f f i c i e n t l y wide t h a t b o t h s u r f a c e s b e g i n t o compete f o r t h e s a m e s o l u t e s i n t h e v i c i n i t y o f t h e f o i l c e n t e r . S i n c e t h e growth r a t e o f t h e d e p l e t e d zone i n c r e a s e s w i t h t empera tu re , i t i s expec ted t h a t t h e d e v i a t i o n b e g i n s ea r l i e r a t h i g h e r t empera tu res . Measurements i n t h i c k e r samples are needed t o estimate t h e bu lk f i l m growth r a t e a t h i g h e r t empera tu res .

According to Okamoto e t a 1 . [ 4 ] , f i l m growth measurements can be used t o de termine damage e f f i c i e n c i e s o f electron i r r a d i a t i o n s r e l a t i v e t o t h o s e of o t h e r p a r t i c l e i r r a d i a t i o n s . G e n e r a l l y , it is p o i n t e d o u t t h a t e l e c t r o n i r r a d i a t i o n produces m i c r o s t r u c t u r a l changes more q u i c k l y on dpa b a s i s t han heavy i o n i r r a d i a t i o n s [ 5 ] [ 6 ] . T h e r e f o r e , e s t i m a t i o n of t h e d e f e c t p r o d u c t i o n e f f i c i e n c y o f e l e c t r o n i r r a d i a t i o n a t e l e v a t e d

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SURFACE SEGREGATION MEASUREMENTS DURING ELECTRON IRRADIATION 165

t e m p e r a t u r e s w i l l be h e l p f u l i n c o r r e l a t i n g e l e c t r o n i r r a d i a t i o n data t o t h o s e by o t h e r p a r t i c l e i r r a d i a t i o n s and t h o s e under reactor env i ronmen t s . These e s t i m a t i o n and d i s c u s s i o n w i l l be c o n t i n u e d e l s e w h e r e [ 7 I . ACKNOWLEDGEMENTS

W e w i sh to acknowledge D r . L.E. Rehn, D r . R . S . Averback and D r . W.E. King f o r many s t i m u l a t i n g a d v i s e s and d i s c u s s i o n s . W e are a l so g r a t e f u l t o M r . B . J . Kestel, M r . P.M. Baldo, M r . E . Ryan and M r . A. P h i l i p p i d e s f o r many e x p e r i m e n t a l a s s i s t a n c e s .

REFERENCES

P . R . Okamoto and L.E. Rehn; J. Nucl . Mater. - 83 , 2 ( 1 9 7 9 ) . J . W . Corbett ; S o l i d S t a t e P h y s i c s , Supp l .7 , 6(Academic P r e s s , New York, 1 9 6 6 ) . L.E. Rehn, P.R. Okamoto, R.S. Averback, W . Wagner andH. Wiedersich; S c r i p t a M e t . - 1 6 , 6 3 9 ( 1 9 8 2 ) . P.R. Okamoto, L . E . Rehn and R.S. Averback; J. Nucl . Mater. 108&109, 319 (1982) . F.A. Garner e t a l . ; R a d i a t i o n E f f e c t s i n Breeder Reactor S t r u c t u r a l Materials. 543(TMS-AIME, 1 9 7 7 ) . T . M u r o z ; K . Fukuya, H: Kawanishi and S . I s h i n o ; J. Nucl . Mater. 103&104, 1349 (1981) . T . Muroga, S. I s h i n o , P . R . Okamoto and H . Wiede r s i ch ; t o be p u b l i s h e d .

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