SURFACE SEGREGATION IN A Fe-5at.%Cr ALLOY

HAL Id: jpa-00225691

https://hal.archives-ouvertes.fr/jpa-00225691

Submitted on 1 Jan 1986

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

SURFACE SEGREGATION IN A Fe-5at.%Cr ALLOY

N. Igata, S. Sato, T. Ando, T. Hashizume, A. Jimbo, T. Sakurai

To cite this version:

N. Igata, S. Sato, T. Ando, T. Hashizume, A. Jimbo, et al.. SURFACE SEGREGATION IN A Fe-5at.%Cr ALLOY. Journal de Physique Colloques, 1986, 47 (C2), pp.C2-371-C2-374.

�10.1051/jphyscol:1986257�. �jpa-00225691�

SURFACE SEGREGATION IN A F e - 5 a t . % C r ALLOY

N . I G A T A , S . SATO, T . ANDO, T . HASHIZUMEI, A . JIMBO' and

T . SAKURAI'

Department of Materials Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan

'The Institute for Solid Start Physics, The University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan

A b s t r a c t - T h e s e g r e g a t i o n o f c h r o m i u m i n s t e e l is i n t e r s t e d b e c a u s e c h r o m i u m h a s a g o o d a n t i - c o r r o s i o n p r o p e r t y . T h e o b j e c t i v e o f t h i s s t u d y i s t o c l a r i f y t h e s u r f a c e s e g r e g a t i o n o f chromium a t o m s i n a Fe- 5 a t . % C r a l l o y . T h e r e w a s n o s e g r e g a t i o n i n t h e b u l k a n a l y s i s o f t h e s p e c i m e n a f t e r s o l u t i o n t r e a t m e n t . However a f t e r t e m p e r i n g a t 7000C s u r f a c e s e g r e g a t i o n o f c h r o m i u m w a s o b s e r v e d . I n ( 1 1 0 ) , s e g r e g a t i o n w a s o b s e r v e d a t t h e f i r s t l a y e r . I n ( 1 0 0 ) a n d ( 1 2 1 ) , s e g r e g a t i o n w a s o b s e r v e d a t t h e f i r s t two l a y e r s . I n ( I l l ) , s e g r e g a t i o n was o b s e r v e d w i t h i n t h e s u r f a c e t h r e e a t o m i c l a y e r s . T h o s e b e h a v i o r s c a n b e u n d e r s t o o d by t h e g e o m e t r y o f t h e a t o m i c s t r u c t u r e .

I-INTRODUCTION

T h e s u r f a c e s e g r a t i o n i s c l o s e l y r e l a t e d t o t h e c h e m i c a l p r o p e r t y o f t h e s u r f a c e . E s p e c i a l l y s u r f a c e s e g r e g a t i o n o f c h r o m i u m i s q u i t e a n i m p o r t a n t p r o b l e m b e c a u s e s t e e l i n c l u d i n g chromium h a s a n t i - c o r r o s i o n p r o p e r t y . H i t h e r t o t h e s e s t u d i e s h a s b e e n d o n e by a u g e r e l e c t r o n s p e c t r o s c o p y / 1 , 2 / a n d atom-probe(AP) / 3 / . As f o r t h e s u r f a c e s e g r e g a t i o n t h e o n l y t e m p e r a t u r e d e p e n d e n c e i n o n e t i p was o b s e r v e d a n d n o o r i e n t a - t i o n d e p e n d e n c e was r e p o r t e d / 3 / . I n t h i s i n v e s t i g a t i o n t h e s e g r e g a t i o n o f chromium w a s i n v e s t i g a t e d i n a F e - 5 a t . % C r a l l o y u s i n g AP. T h e o b j e c t i v e o f t h i s s t u d y i s t o c l a r i f y t h e o r i e n t a t i o n d e p e n d e n c e of s u r f a c e s e g r e g a t i o n by i n - s i t u h e a t i n g i n terms o f a t o m i c s t r u c t u r e .

I1 - EXPERIMENTAL

The m a t e r i a l was a r c - m e l t e d i n Ar a t m o s p h e r e by u s i n g J o h n s o n M a t t h e y ' s p u r e i r o n a n d h i g h p u r i t y Cr(99.99%). A f t e r r o l l i n g a n d a n n e a l i n g , a 2mm t h i c k p l a t e was o b t a i n e d a n d f r o m t h i s s h e e t a 0.2mmx w i r e w a s made. C h e m i c a l c o m p o s i t i o n s i s O.OObat.%C, 0.004 a t . 2 0 , 5 . 3 5 a t . % C r , a n d b a l a n c e F e . T h e s p e c i m e n w a s s e a l e d i n q u a r t z t u b e i n vacuum o f Z X ~ O - ~ P ~ and s o l u t i o n q u e n c h e d a f t e r h e a t i n g l150°C o r 6 0 min. T h e i n - s i t u h e a t i n g w a s p e r f o r m e d a t 7 0 0 9 : f o r 15 s e c a n d 6 0 s e c b y d i r e c t e l e c t r i c c u r r e n t z h e a n a l y s i s was d o n e by b o t h t r a n s m i s s i o n e l e c t r o n microscope(TEM) a n d AP.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986257

JOURNAL DE PHYSIQUE

I11 - EXPERIMENTAL RESULTS

P h o t o 1 s h o w s t h e TEM o b s e r v a t i o n o f t h e s o l u t i o n t r e a t e d s p e c i m e n . T h i s i s m a r t e n s i t e s t r u c t u r e w i t h h i g h d i s l o c a t i o n d e n s i t y . P h o t o 2 i s t h e c o r r e s p o n d i n g FIM image. The b r i g h t s p o t s were d i s p e r s e d u n i f o r m l y . T h i s shows t h a t s t r a i n f i e l d and s o l u t e a t o m s a r e u n i f o r m l y d i s t r i b u t e d . I n P h o t o 3 a FIM i m a g e o f t h e s p e c i m e n h e a t e d a t 7000C f o r 6 0 s e c i s shown. T h e f a c e t t i n g s a t ( l o o ) , ( 1 1 0 ) , ( 1 1 1 ) ( 2 1 0 ) a n d (211) were o b s e r v e d . T h i s shows t h a t t h e more s t a b l e s u r f a c e forms a f t e r s u r f a c e d i f f u s i o n . F i g . 1 s h o w s t h e number o f C r a t o m s a s a f u n c t i o n o f t o t a l e v a p o r a t e d a t o m s . T h e r e w a s s u r f a c e s e g r e g a t i o n a n d a f t e r t h a t C r c o n c e n t r a t i o n b e c o m e s t o a l m o s t z e r o . And a t s u r f a c e l a y e r a b o u t 1 / 3 1 / 2 C r a t o m s w e r e d e t e c t e d as CrO.

T h i s i s c o n s i d e r e d t o b e d u e t o t h e e f f e c t o f o x y g e n a t o m s i n t h e a t m o s p h e r e . I n Fig.2 t h e m i c r o s e g r e g a t i o n o f C r a t o m s a r e shown. I n ( 1 1 0 ) t h e Cr a t o m s s e g r e g a t e d o n l y i n t h e f i r s t a t o m i c l a y e r a n d i t s c o n c e n t r a t i o n was a b o u t 8 0 % . I n ( 1 0 0 ) a n d (121) t h e c o n c e n t r a t i o n of Cr a t o m s r e a c h e d t o 6 0 80% i n t h e f i r s t l a y e r and i n t h e s e c o n d l a y e r i t became t o 40% a n d i n t h e t h i r d l a y e r t o 0%. On t h e o t h e r h a n d i n (111) t h e r e were 50% Cr atoms e v e n i n t h e t h i r d l a y e r , b u t i n t h e f o u r t h l a y e r Cr

P h o t o 1.

-

T r a n s m i s s i o n e l e c t r o n m i c r o p h o t o g r a p h o f a n i r o n - 5 a t . % c h r o m i u m a l l o y s o l u t i o n a n n e a l e d a t 1150°C f o r l h r and quenched.

Photo 2. - F i e l d i o n microphotograph of a n iron-5at.%chromium a 1 lo y s o l u t i o n a n n e a l e d a t 1150°C f o r l h r and quenched.

( 1 1 0 ) , 59% a n d 48% f o r ( 1 0 0 ) a n d ( 1 2 1 )

,

r e s p e c t i v e l y

,

a n d 3 4 % f o r (111). T h i s seems t o be c o r r e s p o n d e n t t o t h e r e s u l t s o f m i c r o s e g r e a t i o n i n one a t o m i c l a y e r i n (110), i n two a t o m i c l a y e r s i n (111) and (121) and i n t h r e e a t o m i c l a y e r s i n (111).

Photo 3. - Thermal f a c e t t i n g of a n iron-5at.%chromium tempered a t 7000C f o r 6 0 s e c i n vacuum.

N U M B E R O F T O T A L A T O M S

F i g . 1.

-

C u m u l a t i v e number o f C r a n d CrO a t o m s v e r s u s c u m u l a t i v e number of Fe+Cr atoms i n a n i r o n - 5at.%chromium a l l o y tempered a t 7000C f o r 1 5 s e c i n vacuum.

JOURNAL DE _PHYSIQUE

Ann. Temp. 7000C ann. time O(110) 15sec A(100) 60sec A(121) 60sec

~ ( 1 1 1 ) 6Osec

0 1 2 3 4 5 6 7

D E P T H (layer)

Fig. 2.

-

Orientation dependence of surface segregation of chromium.

Fig. 3. - Surface structures of atom in (110), (loo), (111) and (121). The atomic coverage of the surface is 84%, 59%, 48% and 34% for (110), (loo), (121) and (Ill), respectively.

IV

-

SUMMARY

In this study the microsegregation of Cr atoms at surface in a Fe-5at.%Cr alloy was revealed.

(1) The microsegregation was observed in one atomic layer in (llO),in two atomic layers in (100) and (121), in three atomic layers in (111).

(2) It was revealed that the depth of microsegregation was different depending on the stacking of atoms in each surface. This information was obtained only by FIM and AP.

REFERENCES

/l/ Briant, C. L. and Mulford,

R.

A., Metallurgical Transactions 13A (1982) 745.

/2/ Leygraf,

C.,

Hultquist, G. and Ekelund, S., Surface Science 46 (1974) 157.

/3/ Krishnaswamy, S. V., McLane, S. B. and Muller, E. W.,

J.

Vac. Sci. Technol. 11 (1974) 899.