Plastic zone sizes in fatigued specimens of INCO 718
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1.2
0.8
I
i
i
,
,
$~
,
L
VALUE FROM ERESH ERACTUflE (907o INTERGRANULAR)
1.0 BORON PEAK HEIGHT (Arb. Scale)
i
M. C L A V E L , D. FOURNIER, AND A. PINEAU
84
0.6 0.4 0.2 0 0
Plastic Zone Sizes in Fatigued Specimens of INCO 718
i0
20
30
40
50
60
= 20}30
ATOMIC LAYERS REMOVED
Fig. 2 - - B o r o n c o n c e n t r a t i o n prof~l~ in t e r m s of b o r o n (181 eV)
peak height vs atomic layers removed by argon ion sputtering. u l a r f a c e t s w a s o b t a i n e d by d e t e r m i n i n g the b o r o n c o n c e n t r a t i o n p r o f i l e , i . e . , the A u g e r b o r o n p e a k h e i g h t a s a function of depth b e n e a t h the f r a c t u r e s u r f a c e . The p r o f i l e , p r e s e n t e d in Fig. 2, was o b t a i n e d by c o n t r o l l e d s p u t t e r i n g (by a r g o n ion b o m b a r d m e n t ) of m a t e r i a l f r o m the f r a c t u r e s u r f a c e in s m a l l s t e p s and p e r f o r m i n g A u g e r a n a l y s i s for b o r o n at each s t e p . The r a p i d d e c r e a s e in b o r o n c o n c e n t r a t i o n in the f i r s t 10 a t o m i c l a y e r s , followed by a m o r e g r a d u a l d e c r e a s e out to a p p r o x i m a t e l y 2000 a t o m i c l a y e r s s u g g e s t s the p r e s e n c e of both e q u i l i b r i u m s e g r e g a t i o n (Gibbsian a d s o r p t i o n ) and n o n e q u i l i b r i u m s e g r e g a t i o n (from d i f fusion of v a c a n c y / b o r o n c o m p l e x e s to g r a i n b o u n d a r i e s d u r i n g c o o l i n g f r o m high t e m p e r a t u r e s ) . The f a c t that the s t r o n g m o l y b d e n u m A u g e r p e a k at 183 eV s w a s not d e t e c t e d , i n d i c a t e d t h a t m o l y b d e n u m was not s e g r e g a t e d at the g r a i n b o u n d a r i e s . In s u m m a r y , the p r e s e n t c o m m u n i c a t i o n r e p o r t s the o b s e r v a t i o n of two p o s i t i o n s for the p r i n c i p a l Auger p e a k f o r b o r o n , one at 181 eV for e l e m e n t a l b o r o n , and one at 170 eV for b o r o n c h e m i c a l l y bound in a p h a s e c o m m o n l y found in b o r o n s t e e l s , Fe2s(C , B) 6. While t h i s c h e m i c a l shift of the A u g e r b o r o n p e a k and s i m i l a r s h i f t s r e p o r t e d for A1, Ta and Si a r e of g e n e r a l s c i e n t i f i c i n t e r e s t , the p r e s e n t o b s e r v a t i o n r e g a r d i n g elemental boron carries special metallurgical signific a n c e b e c a u s e it a p p e a r s to be t h e f i r s t d i r e c t e v i d e n c e for s e g r e g a t i o n of a t o m i c b o r o n at g r a i n b o u n d a r i e s in s t e e l . The door is now open for the a p p l i c a t i o n of 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 to the s t u d y of g r a i n b o u n d a r y s e g r e g a t i o n of b o r o n in s t e e l , h o p e f u l l y l e a d i n g to an u n d e r s t a n d i n g of the r e s p e c t i v e e f f e c t s of a t o m i c b o r o n and of p r e c i p i t a t e d b o r o n - c o n t a i n
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