QUANTITATIVE TRANSMISSION ANALYTICAL MICROSCOPY OF SUPERALLOYS

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QUANTITATIVE TRANSMISSION ANALYTICAL MICROSCOPY OF SUPERALLOYS

W. Voice, R. Faulkner

To cite this version:

W. Voice, R. Faulkner. QUANTITATIVE TRANSMISSION ANALYTICAL MICROSCOPY OF SUPERALLOYS. Journal de Physique Colloques, 1984, 45 (C2), pp.C2-415-C2-417.

�10.1051/jphyscol:1984294�. �jpa-00224009�

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JOURNAL DE PHYSIQUE

Colloque C2, supplkment au n02, Tome 45,

fCvrier

1984 page .C2-4

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QUANTITATIVE TRANSMISSION ANALYTICAL MICROSCOPY OF SUPERALLOYS

W.E. Voice and R.G. Faulkner

Department of Materials Engineering and Design, Loughborough University of Technology, Loughborough, Leicestershire LE11 3TU, U.K.

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On montre que l ' u t i l i s a t i o n d'une n o u v e l l e mgthode de c o r r e c t i o n pour l a microanalyse d e s lames minces conduit

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des r g s u l t a t s s a t i s f a i s a n t s dans l e c a s d'un s u p e r - a l l i a g e complexe ( C 2 6 3 ) . La mgthode e s t p a r t i c u l i s - rement e f f i c a c e l o r s q u ' o n n ' u t i l i s e que d e s r a i e s e t q u ' i l n ' y a pas de f l u o r e s c e n c e . On montre que l e s e f f e t s d ' a b s o r p t i o n e t d e f l u o r e s c e n c e n e s o n t pas n d g l i g e a b l e s dans l e s lames minces.

A b s t r a c t

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Application of a new c o r r e c t i o n procedure f o r t h i n f i l m m i c r o a n a l y s i s has been shown t o work reasonably w e l l f o r a complex super- a l l o y , C263. The procedure i s p a r t i c u l a r l y s u c c e s s f u l when a p p l i e d t o systems where only K l i n e s a r e p r e s e n t and when no f l u o r e s c e n c e o c c u r s . I t i s shown t h a t a b s o r p t i o n and f l u o r e s c e n c e e f f e c t s cannot be n e g l e c t e d i n t h i n f i l m s .

INTRODUCTION

A procedure f o r making q u a n t i t a t i v e X-ray a n a l y s i s of t h i n f o i l s i n Scanning Trans- mission E l e c t r o n Microscopes (STEM) has r e c e n t l y been developed ( 1 ) . This standard- l e s s technique p r e d i c t s c o r r e c t i o n parameters based on t h i c k n e s s of f o i l , specimen geometry and e l e c t r o n microscope i n s t r u m e n t a l v a r i a b l e s . Monte Carlo computer s i m u l a t i o n is used t o c h a r a c t e r i s e t h e d i s t r i b u t i o n of X-ray g e n e r a t i o n w i t h i n t h e f o i l and numerical i n t e g r a t i o n v i a a computer c o r r e c t s f o r a b s o r p t i o n and specimen geometry. The v a l i d i t y of t h i s method i s c o n t i n u a l l y checked u s i n g a wide range of a l l o y s of known composition. E a r l y r e s u l t s o b t a i n e d from a nickel-base s u p e r a l l o y a r e p r e s e n t e d h e r e .

(1) Voice, W.E. and Faulkner, R.G. This Conference.

THEORY

The computer programme d e s c r i b e d i n (1) has been run f o r a nickel-base s u p e r a l l o y , C263 a t v a r y i n g specimen t h i c k n e s s e s and t i l t s f o r a lOOkV a c c e l e r a t i n g v o l t a g e . An assumed normalised c o n c e n t r a t i o n , C f o r t h e s u p e r a l l o y being s t u d i e d i s d e t e r - mined i n t h e e l e c t r o n probe microanalyser (EPMA). A Then t h e programme p r e d i c t s t h e r e l a t i v e numbers of c o u n t s , I A TH) f o r each element produced under t h e experimental c o n d i t i o n s p r e v i o u s l y d e s c r i b e & . Hence

k i s

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c o r r e c t i o n f a c t o r which can subsequently be a p p l i e d t o raw i n t e n s i t y d a t a , I , o b t a i n e d from m a t e r i a l s s u b j e c t e d t o i n d e n t i c a l experiment c o n d i t i o n s t o g i v e r e a l c o n c e n t r a t i o n s . The t h e o r y c u r r e n t l y t a k e s no account of f l u o r e s c e n c e . A

The graphs of p r e d i c t e d I as a f u n c t i o n of f i l m t h i c k n e s s and specimen t i l t a r e shown i n F i g s . 2 and t I T H ) r e s p e c t i v e l y .

THICKNESS MEASUREMENT

F o i l t h i c k n e s s i s widely determined by measuring t h e d i s t a n c e between t h e base of

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984294

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C2-416 JOURNAL

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PHYSIQUE

t h e s u r f a c e carbon d e p o s i t s produced d u r i n g s p o t a n a l y s i s . This i s known t o g i v e a c o n s i s t e n t o v e r e s t i m a t e of t h i c k n e s s due t o t h e base of t h e cones s p r e a d i n g along t h e s u r f a c e s o t h a t t h e p o s i t i o n of t h e i n t e r f a c e between t h e carbon d e p o s i t and f o i l cannot be d i s t i n g u i s h e d e x a c t l y ( 2 ) . The method used i n t h i s work i s t o t i l t t h e specimen by 90° t o t h e a n a l y s i s p o s i t i o n and t o r e c o r d t h e a n a l y s i s d e p o s i t i n STEM ( F i g . l a ) and scanning e l e c t r o n microscopy (SEM) ( F i g . l b ) . The f o i l i s t h e n turned o v e r i n t h e specimen h o l d e r and an SEM image i s recorded of t h e lower s u r f a c e d e p o s i t ( F i g . 1 ~ ) . The d i f f e r e n c e of t h e d i s t a n c e between t h e p o i n t s of t h e two s u r f a c e d e p o s i t s from STEM and t h e sum of t h e h e i g h t s of t h e i n d i v i d u a l d e p o s i t s i n t h e SEM images g i v e s t h e f o i l t h i c k n e s s / c o s ( t i l t a n g l e ) .

(2) Rae, D . A . , S c o t t , V.D. and Love, G. " Q u a n t i t a t i v e Microanalysis with High S p a t i a l Resolution". Metal S o c i e t y Conference, UMIST/MANCHESTER, March 1981.

EXPERIMENTAL PROCEDURE AND RESULTS

The a l l o y s t u d i e d , C263, i s a n a l y s e d i n bulk form i n EPMA. The ZAF (COR2) c o r r e c t - ed a n a l y s i s i s as f o l l o w s

This i s a normalised composition: elements p r e s e n t i n q u a n t i t i e s l e s s t h a n l w t % (Al, F e , Mn, S i ) a r e o m i t t e d . This i s t h e assumed composition CA used i n t h e computer programme p r e d i c t i o n of raw i n t e n s i t i e s , I

.

Fig.6 shows t h e r e g i o n of t h i n f o i l i n v e s t i g a t e d i n t h e STEM. R e l a t i v e numbe$Bmbf counts f o r t h e major elements determined i n a JEOL 100CX/Link systems 860 STEMMA a s a f u n c t i o n of f i l m t h i c k n e s s and t i l t a r e shown i n F i g s . 3 and 5 r e s p e c t i v e l y . Background and peak o v e r l a p f a c t o r s a r e accomodatedin t h e Link ZAF programme.

DISCUSSION

To confirm t h e v a l i d i t y of t h e p r e d i c t i o n s a graph of p r e d i c t e d c o n c e n t r a t i o n as a f u n c t i o n o f f i l m t h i c k n e s s i s shown i n F i g . 7 . The v e r t i c a l a x i s u n i t s a r e d e t e r - mined by m u l t i p l y i n g t h e p r a c t i c a l l y observed p r o p o r t i o n of counts by t h e c o r r e c t i o n f a c t o r , k (CA/IA(TH)).

Fig. 7 shows t h a t reasonably c o n s t a n t v a l u e s of composition a r e o b t a i n e d . Chromium l e v e l s a r e t o o high and t h i s i s thought t o be due t o f l u o r e s c e n c e of C r K, by i r o n and n i c k e l K,. Also T i Ka i s f l u o r e s c e d by C r K,. Fluorescence has n o t y e t been included i n t h e c o r r e c t i o n procedure. Another p o s s i b l e e x p l a n a t i o n f o r t h e poor chromium r e s u l t i s t h a t t h e i o n i s a t i o n e f f i c i e n c i e s a r e c a l c u l a t e d on t h e b a s i s of t h e d a t a o b t a i n e d a t 20/30 kV, and n o t a t 100 kV a s i s t h e c a s e f o r STEMMA work.

Molybdenum has n o t been included i n t h e a n a l y s i s because t h e energy d i s p e r s i v e a n a l y s e r i s not capable of d i s t i n g u i s h i n g between molybdenum L, and LB peaks. Also no r e l i a b l e d a t a a r e a v a i l a b l e f o r i o n i s a t i o n e f f i c i e n c i e s f o r L, and Lg l i n e s , e s p e c i a l l y a t high a c c e l e r a t i n g v o l t a g e s .

SUMMARY AND FUTURE WORK

Application of a new c o r r e c t i o n procedure f o r t h i n f i l m m i c r o a n a l y s i s has been shown t o work reasonably w e l l f o r a complex s u p e r a l l o y , C263. The procedure i s p a r t i c u l a r - l y s u c c e s s f u l when a p p l i e d t o systems where only K, l i n e s a r e p r e s e n t and when no f l u o r e s c e n c e i s o c c u r r i n g . This p a p e r , t o g e t h e r with i t s CO-paper i n t h i s conference ( l ) , show t h a t a b s o r p t i o n and f l u o r e s c e n c e e f f e c t s cannot be n e g l e c t e d i n t h i n f i l m s .

F u r t h e r work is i n p r o g r e s s t o q u a n t i f y 1 ) Fluorescence ;

2) I o n i s a t i o n e f f i c i e n c y c o n s t a n t s f o r L and M l i n e s a t high a c c e l e r a t i n g v o l t a g e s .

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