ATOM PROBE FIELD-ION MICROSCOPY OF CONVENTIONALLY CAST & MELT-SPUN NICKEL ALUMINIDE ALLOYS CONTAINING BORON AND HAFNIUM

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ATOM PROBE FIELD-ION MICROSCOPY OF CONVENTIONALLY CAST & MELT-SPUN NICKEL

ALUMINIDE ALLOYS CONTAINING BORON AND HAFNIUM

D. Sieloff, S. Brenner, M. Burke

To cite this version:

D. Sieloff, S. Brenner, M. Burke. ATOM PROBE FIELD-ION MICROSCOPY OF CONVENTIONALLY CAST & MELT-SPUN NICKEL ALUMINIDE ALLOYS CONTAINING BORON AND HAFNIUM. Journal de Physique Colloques, 1986, 47 (C7), pp.C7-289-C7-293.

�10.1051/jphyscol:1986750�. �jpa-00225945�

JOURNAL DE PHYSIQUE

Colloque C7, supplement au n o 11, Tome 47, Novembre 1986

ATOM PROBE FIELD-ION MICROSCOPY OF CONVENTIONALLY CAST & MELT-SPUN NICKEL ALUMINIDE ALLOYS CONTAINING BORON AND HAFNIUM

D.D. SIELOFF, S.S. BRENNER and M.G. BURKE

Department of Materials Science and Engineering, University of Pittsburgh, Pittsburgh, PA 15261, U.S.A.

ABSTRACT - I n t h i s p a p e r , we r e p o r t u p o n f u r t h e r r e s u l t s o n b o r o r - doped N i 3 A 1 a 1 l o y s i n c l u d i n g t h e g r a i n b o u n d z r y c h e m i s t r y of m e l t -

s p u n and c o n v e n t i o n a l l y c a s t m a t e r i a l s .

I. INTRODUCTION

S m a l l a d d i t i o n s o f b o r o n m a r k e d l y i n c r e a s e t h e room t e m p e r a t u r e d u c t i l i t y o f N i 3 A 1 p r o v i d e d t h a t t h e aluminum c o n c e n t r a t i o n i s l e s s t h a n s t o i c h i o m e t r i c [ I ] . E.M. S c h u l s o n e t a l . 1 2 1 c o n c l u d e d f r o m s t u d i e s o f t h e m e c h a n i c a l p r o p e r t i e s o f b o r o n - d o p e d N i 3 A 1 t h a t t h e b o r o n h e l p s t h e g r a i n b o u n d a r i e s t o a c c o m m o d a t e s l i p d u r l n g p l a s t i c d e f o r m a t i o n , t h u s r e d u c i n g t h e i n c i d e n c e o f d i s l o c a t i o n p i l e - u p s , and, c o n s e q u e n t l y , c r a c k i n i t i a t i o n . W h i l e t h i s model i s c o n s i s t e n t w i t h t h e o b s e r v a t i o n o f b o r o n s e g r e g a t i o n t o g r a i n b o u n d a r i e s i n N i 3 A 1

[ 3 , 4 ! , i t d o e s n o t e x p l a i n t h e m e c h a n i s m w h e r e b y t h i s o c c u r s n o r t h e e f f e c t of aluminum c o n t e n t on t h e ductility.

To g a i n a b e t t e r u n d e r s t a n d i n g o f t h e e f f e c t s o f b o r o n a n 2 a l u m i n u m c o n c e n t r a t i o n o n d u c t i l i t y , we h a v e u s e d t h e a t o m p r o b e t o i n e a s u r e t h e c o m p o s i t i o n o f t h e g r a i n b o u n d a r y r e g i o n s i n h y p o s t o i c h i o m e t r i c N i 3 A 1 a 1 l o y s . T h e a t o m p r o b e h a s t h e a d v a n t a q e o v e r A u g e r s p e c t r o s c o p y , w h i c h i s c u r r e n t l y u s e d f o r g r a i n b o u n d a r y s t u d i e s , i n t h a t i t i s n o t n e c e s s a r y t o f r a c t u r e t h e s p e c i m e n i n o r d e r t o e x p o s e t h e g r a i n b o u n d a r y p l a n e . The two t e c h n i q u e s a r e b i a s e d i n o p p o s i t e d i r e c t i o n s w i t h r e s p e c t t o b o u n d a r y s e l e c t i o n . I n Auvez s p e c t r o s c o p y , t h e m o s t b r i t t l e i n t e r f a c e s a r e e x p o s e d a n d a n a l y z e d , w h i l e i n atom p r o b e m i c r o a n a l y s i s t h e more d u c t i l e b o u n d a r i e s t e n d t o b e i n v e s t i g a t e d s i n c e t h e y a r e l e s s l i k e l y t o c a u s e s p e c i n e n f a i l u r e . I n t h i s p a p e r , w e d e s c r i b e t h e a n a l y s e s o f g r a i n b o u n d a r y r e g i o n s i n two n i c k e l a l u m i n i d e a 1 l o y s .

I I . EXPERIMENTAL

Two a l l o y s , s u p p l i e d b y Oak R i d g e N a t i o n a l L a b o r a t o r y , w e r e i n v e s t i g a t e d . The c o m p o s i t i o n ( a t . % ) of t h e n i c k e l a l u m i n i d e a 1 l o y o a r e :

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986750

JOURNAL

DE

PHYSIQUE

T h e t w o a l l o y s w e r e s w a g e d a n d w i r e d r a w n a f t e r w h i c h t h e y w e r e a n n e a l e d a t 1 0 7 3 K t o p r o d u c e a f i n e - g r a i n e d r e c r y s t a l l i z e d m i c r o s t r u c t u r e . N e e d l e - s h a p e d s p e c i m e n s were p r e p a r e d i n t h e u s u a l manner I 5 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 s c o p y was u s e d e x t e n s i v e l y i n o r d e r t o p r e s e l e c t s p e c i m e n s w i t h g r a i n b o u n d a r i e s i n t e r s e c t i n g t h e t i p s u r f a c e . I n a d d i t i o n , a l l o y IC-15-16 was s u p p l i e d i n t h e f o r m o f m e l t - s p u n r i b b o n . T h i s m a t e r i a l was a l s o examined by APFIM and TEM.

A s t r a i g h t t-o-f atom p r o b e w i t h specimen c o o l i n g c a p a b i l i t y t o a p p r o x i m a t e l y 20 K was u s e d f o r t h e a n a l y s e s . The h y d r o g e n background p r e s s u r e , m o n i t o r e d w i t h a q u a d r o p o l e a n a l y z e r , was m a i n t a i n e d a s low a s p o s s i b l e t o r e d u c e t h e f o r m a t i o n o f h y d r i d e s a n d p o s s i b l e c o m p o s i t i o n e r r o r s . A 1 1 a n a l y s e s w e r e c o n d u c t e d a t 50 K a n d w i t h a p u l s e f r a c t i o n o f 1 5 % . T h e s e c o n d i t i o n s were p r e v i o u s l y shown t o p r o v i d e r e a s o n a b l e ' m i c r o c h e m i c a l d a t a i n n i c k e l a l u m i n i d e a l l o y s [ 6 ] .

111. RESULTS & DISCUSSION

T h e c o m p o s i t i o n o f t h e g r a i n b o u n d a r y r e g i o n s i n t h e r e c r y s t a l 1 iz e d m a t e r i a l showed c o n s i d e r a b l e £ 1 u c t u a t i o n s . G e n e r a l 1 y , a b o r o n c o n c e n t r a t i o n o f a p p r o x i m a t e l y 1 t o 3 a t . % w a s m e a s u r e d w i t h t h e p r o b e h o l e c e n t e r e d on t h e g r a i n boundary. T h i s c o r r e s p o n d s t o a n e n r i c h m e n t of

-

^{10. A} t y p i c a l a n a l y s i s i s p r e s e n t e d i n F i g u r e 1. The r e s u l t s o f numerous g r a i n b o u n d a r y a n a l y s e s i n d i c a t e s t h a t t h e b o r o n c o n c e n t r a t i o n i s p r o b a b l y n o t uniforrn w i t h i n t h e a r e a o f a n a l y s i s , b u t m o s t l i k e l y p e a k s a t t h e g r a i n b o u n d a r y p l a n e . The c o n c e n t r a t i o n p r o f i l e o f b o r o n a t t h e b o u n d a r i e s c a n n o t b e v e r y s h a r p s i n c e a b o r o n e n r i c h m e n t was d e t e c t e d a t d i s t a n c e s g r e a t e r t h a n 10 atom d i a m e t e r s from some g r a i n b o u n d a r i e s .

P a r t i c u l a r a t t e n t i o n was p a i d t o t h e aluminum c o n c e n t r a t i o n o f t h e g r a i n b o u n d a r i e s a n d n e a r - b o u n d a r y r e g i o n s . An u n u s u a l l y l o w aluminum c o n t e n t was m e a s u r e d i n t h e v i c i n i t y of some g r a i n b o u n d a r i e s when t h e b o r o n c o n c e n t r a t i o n i n t h e same r e g i o n was h i g h . An e x a m p l e f r o m a 1 l o y I C - 5 0 - 8 i s shown i n F i g u r e 2. T h e a v e r a g e a l u m i n u m c o n c e n t r a t i o n w a s 23.5 a t . % i n t h i s a l l o y , b u t a d e c r e a s e t o 19.4

+/-

0.9 a t . % was m e a s u r e d i n t h e v i c i n i t y of t h e boundary. T h i s d e p l e t i o n p e r s i s t e d o v e r - 3 p r o b e h o l e d i a m e t e r s away f r o m t h e g r a i n boundary.

AP a n a l y s i s a p p r o x i m a t e l y 8 nm away f r o m t h e b o u n d a r y r e v e a l e d t h a t t h e a l u m i n u m c o n c e n t r a t i o n was 23.7

+ / -

1.3 a t . % , t h e n o m i n a l c o m p o s i t i o n . A d e c r e a s e o f s e v e r a l p e r c e n t i n t h e a l u m i n u ~ c o n c e n t r a t i o n o f t h e g r a i n b o u n d a r y r e g i o n may c o n c e i v a b l y p r o d u c e s u b s t a n t i a l d i s o r d e r i n 7 o f t h e L l s t r u c t u r e o f t h e a l l o y . S u c h d i s o r d e r i n g d o e s n o t seem t o o c c u r . % h i s i s e v i d e n t from t h e a n a l y s i s o f t h e ( 2 0 0 ) s u p e r l a t t i c e p l a n e s t r a v e r s e d b y a b o u n d a r y ( F i g u r e 3 ) . '!he d a t a o b t a i n e d f r o m t h i s a n a l y s i s s t i l l r e v e a l s a h i g h d e g r e e o f o r d e r up t o t h e boundary.

D e t a i l e d atom p r o b e a n a l y s i s of a 15O t i l t b o u n d a r y i n t h e m e l t - s ? u n a l l o y r e v e a l e d a n i n c r e a s e i n b o r o n c o n t e n t i n t h e v i c i n i t y o f t h e b o u n d a r y , a n d i n c o n t r a s t w i t h t h e c o n v e n t i o n a l l y c a s t m a t e r i a l , a n i n c r e a s e i n a l u m i n u m c o n t e n t t o 28 s t . % . T h i s i s s i m i l a r t o t h e d a t a o b t a i n e d a t ORNL o n s p l a t - q u e n c h e d a 1 l o y s [4].

An o b s e r v a t i o n f r o m t h e e x a m i n a t i o n of t h e c o n v e n t i o n a l l y c a s t a l l o y s which i s i n a g r e e m e n t w i t h r e s u l t s o f t h e s t u d y b y M i l l e r and H o r t o n [ 4 ] i s t h e d e c o r a t i o n o f some b u t n o t a l l A P B s i n t h e m a t e r i a 1 . An e x a m p l e o f d e c o r a t e d APBs i s p r e s e n t e d i n F i g u r e 4. No g r a i n boundary p h a s e s w e r e o b s e r v e d i n t h e c a s t and r e c r y s t a l l i z e d a 1 lo y s u n l i k e t h e o b s e r v a t i o n s from t h e s p l a t - q u e n c h e d a 1 l o y s [ 4 ] .

H a f n i u m e n r i c h m e n t was m e a s u r e d a t some g a i n b o u n d a r i e s i n t h e cast a l l o y . The e x t e n t of h a f n i u m s e g r e g a t i o n was n o t a s s i q n i f i c a n t a s t h a t o f b o r o n .

I V . CONCLUSIONS

Atom p r o b e a n a l y s i s of r e c r y s t a l l i z e d b u l k N i 3 A 1 c o n f i r m e d t h e s e g r e g a t i o n o f b o r o n t o g r a i n b o u n d a r i e s . T h e b o r o n c o n c e n t r a t i o n seems t o p e a k a t t h e b o u n d a r y p l a n e b u t t h e b o r o n - e n r i c h e d z o n e e x t e n d s t o a minimum o f 5 a t o m l a y e r s f r o m t h e b o u n d a r y . I n a s i g n i f i c a n t n u m b e r o f e x p e r i m e n t s o n t h e c a s t a l l o y s , i t was f o u n d t h a t when t h e b o r o n c o n t e n t w a s h i g h i n t h e v i c i n i t y o f a g r a i n b o u n d a r y , t h e a l u m i n u m c o n c e n t r a t i o n i n t h e s a m e r e g i o n w a s

subs tan ti all:^

d e c r e a s e d a s c o m p a r e d t o t h e a v e r a g e c o m p o s i t i o n . I m p o r t a n t l y , t h e L12 s t r u c t u r e i s p r e s e r v e d w i t h o u t a n y s i g n i f i c a n t d i s o r d e r i n g .

ACKNOWLEDGMENTS

T h i s r e s e a r c h i s s u p p o r t e d b y t h e O f f i c e of B a s i c Energy S c i e n c e s o f t h e Department of Energy u n d e r c o n t r a c t DE-FG02-85ER45213.

REFERENCES

1. C.T. L i u , C.L. W h i t e , and J . A . H o r t o n , A c t a M e t . , 33 ( 1 9 8 5 ) p.213.

2 . E.M. S c h u l s o n , T.P W e i h s , I. B a k e r , H . J . F r o s t , a n d J . A . H o r t o n , A c t a M e t . , 34 ( J u l y , 1 9 8 6 ) p.1395.

----

- -- --

3. C.T. L i u a n d C.L. W h i t e , "The D e s i g n o f D u c t i l e P o l y c r y s t a l l i n e N i 3 A 1 A l l o y s " P r e p r i n t ( 1 9 8 4 ) .

4 . M.K. M i l l e r and J . A . H o r t o n , S c r i p t a Met., 20 ( 1 9 8 6 ) p.789.

5 . S.S. B r e n n e r a n d M . K . M i l l e r , J o u r n a l

of

M e t a l s , 3 5 ( 1 9 8 3 ) p . 5 4 .

6. S.S. B r e n n e r , D.D. S i e l o f f, a n d M.G. B u r k e , P r o c . 3 2 n d I F E S e d . b y M . K . M i l l e r a n d S.S. B r e n n e r ; J . d e P h y s i q u e , C 2 ( 1 9 8 6 ) p.C2-215.

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F i ~ u r e 1. ( a ) F i e l d - i o n m i c r o q r a p h o f boron-doped N i 3 A 1 c o n t a i n i n q a g r a i n b o u n d a r y , a n d ( b ) t h e e v a p o r a t i o n s e q u e n c e d l a q r a m o b t a i n e d d u r i n q t h e a n a l y s i s o f t h a t g r a i n boundarv.

F i g u r e 2. A s e r i e s of f i e l d - i o n m i c r o ~ r a p h s i 1 l u s t r s t i . y t h e l o c a t i o n a n d r e s u l ~ s o f t h r e e a t o m p r o b e a n a l y s e s m o v i n q away f r o m a q r a i n b o u n d a r 11

Ficjure 3. A n a l y s i s of ( 2 0 0 ) s u p e r l a t t i c e p l a n e s t r a v e r s e d b y a c r a i n b o u n d a r y .

F i q u r e 4 . F i e l d - i o n m i c r o c r a p h o f a b o r o n - d e c o r a t e d A P B ( a r r o w e d ) .