ATOM PROBE STUDY OF TITANIUM BASE ALLOYS : PRELIMINARY RESULTS

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ATOM PROBE STUDY OF TITANIUM BASE ALLOYS : PRELIMINARY RESULTS

A. Menand, S. Chambreland, C. Martin

To cite this version:

A. Menand, S. Chambreland, C. Martin. ATOM PROBE STUDY OF TITANIUM BASE AL- LOYS : PRELIMINARY RESULTS. Journal de Physique Colloques, 1986, 47 (C2), pp.C2-197-C2-202.

�10.1051/jphyscol:1986229�. �jpa-00225662�

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Colloque C2, supplément au n 0 3 , Tome 47, mars 1986 page

ATOM PROBE STUDY OF TITANIUM BASE ALLOYS : PRELIMINARY RESULTS

A. MENAND, S. CHAMBRELAND and C. MARTIN

Laboratoire de Microscopie Ionique, U A CNRS 808, UER Sciences de Rouen, B P 67, F-76130 Mont Saint Aignan, France

Résumé - Deux a l l i a g e s à base t i t a n e , T i 4 6 e t Ti88,8 CU^,^ ^A18,g, o n t é t é é t u d i é s à l a sonde atomique. Un p r é c i p i t é de l a phase Ti, A l a é t é analysé dans l ' a l l i a g e b i n a i r e . La microanalyse de l ' a l l i a g e T i Cu A l a r é v é l é l a présence de zones e n r i c h i e s en Cuivre. L'étude a également mis en évidence une p é n é t r a t i o n d'Hydrogène dans l e s é c h a n t i l l o n s probablement due à l a technique de p r é p a r a t i o n . Les r é s u l t a t s obtenus démontrent l a f a i s a b i l i t é d'études d ' a l l i a g e s à base t i t a n e à l a sonde atomique.

A b s t r a c t - Two d i f f e r e n t t i t a n i u m base a l l o y s , T i 4 6 and "2.3 Alg-g, have been s t u d i e d by atom probe microanalysis. A p r e c i p i t a t e of Ti, Al was analysed i n t h e b i n a r y a l l o y s . Elicro-analysis o f T i Cu A l a l l o y revealed t h e presence o f Copper enriched zones. The study has a l s o e x h i b i t e d a p e n e t r a t i o n o f Hydrogen i n t h e samples, probably due t o p r e p a r a t i o n t e c h n i - que. The r e s u l t s demonstrate t h e f e a s a b i l i t y o f s t u d i e s on t i t a n i u m base a l l o y s by mean o f atom probe.

1 - INTRODUCTION

Titanium base a l l o y s a r e o f g r e a t i n t e r e s t p a r t i c u l a r l y i n aerospace i n d u s t r y but, a t t h e authors knowledge, no atom probe study has been y e t reported.

We have attempted t o study two types o f a l l o y s

T i 4 6 and Tiggs8 Cuzs3 A l g a g . The aim o f these i n v e s t i g a t i o n s was t o determine t h e c o r r e c t experimental condi- t i o n s r e q u i r e d t o o b t a i n r e l i a b l e data on t i t a n i u m base a l l o y s .

II - EXPERIMENTAL

The a l l o y s were s u p p l i e d by O. N. E. R. A. ( O f f i c e National dlEtudes e t de Recher- ches Aérospatiales) and were prepared b y u s i n g a r c m e l t i n g technique.

The F i e l d I o n Microscopy (F. 1. M.) specimen were made by anodic e l e c t r o p o l i s h i n g . T i Al samples were p o l i s h e d i n a s o l u t i o n o f 10 % p e r c h l o r i c a c i d i n 2-

Butoxyethanol. T i Cu Al samples were prepared i n an e l e c t r o l y t e composed o f 6 % p e r c h l o r i c acid, 34 % n - b u t y l a l c o h o l and 60 % methanol.

The atom probe used i n t h i s study i s a conventionnal one. The instrument d e t a i l s and performances are described elsewhere I l / . R e l i a b l e data were obtained by u s i n o a p u l s e f r a c t i o n o f 20 % of t h e DC voltage, and a t i p temperature l y i n g between 40 K and 80 K. Analyses were c a r r i e d o u t i n a vacuum o f I O - ' Torr. F. 1. M. observa- t i o n s were performed a t 20 K and Neon gas was used f o r imaging.

III - RESULTS AND DISCUSSION Ti46

--- A154

We have analysed ~ a m p l e s prepared from a l l o y heat t r e a t e d 10 days a t 1073 K a f t e r

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986229

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a s o l u t i o n treatment o f 48 hours a t 1573 K. According t o A. LOISF4U e t a l /2/ t h e T i Al m a t r i x has a s t r u c t u r e LI w i t h a

a ^{and c}

a.

As shown i n f i g u r e 1 Aluminium and Titanium a r e detected as doubly charged ions and t h e f i v e isotopes o f t i t a n i u m a r e c l e a r l y resolved.

Fig. 1 - Atom probe mass spectrum o f a T i 4 6 sample

The composition of T i Al phase i s found equal t o 53

3 a t % o f A l . U n f o r t u n a t l y we d i d n o t succeed t o analyse reproduceiy t h e Ti, Al phase because o f .its v e r y low volume f r a c t i o n , and t h e s h o r t l i f e time of t i p s f o r t h i s very b r i t t l e a l l o y . Only one Ti, Al p r e c i p i t a t e was crossed d u r i n g random area i n v e s t i g a t i o n o f t h e a l l o y , composition p r o f i l e s given i n f i g u r e 2 i l l u s t r a t e such a s i t u a t i o n . The composition o f Ti, Al phase i s founded equal t o 33.7 a t % o f A l .

Ni

F i g . 2 - I n t e g r a l composition p r o f i l e s . The cumulative number o f T i o r A l atoms i s p l o t t e d versus t h e cumulative o f T i + Al atoms.

O

Nt

NUMBER OF IONS DETECTED

F i g . 3 - I n t e g r a l composition p r o f i l e s combined w i t h t h e c o r r e s - ponding i o n f l u x curves.

- Cumulative number o f T i o r Al ions i s p l o t t e d versus t h e cumulative number o f T i

Al i o n s .

- Cumulative number o f evaporation pulses i s p l o t t e d versus t h e cumulative number o f T i + Al ions.

Ti88.8 --- Cu2.3 A18.9

The p e c u l i a r i t y o f titanium-copper a l l o y s i s t h a t age-hardening i s a v a l a i b l e by p r e c i p i t a t i o n o f copper enriched zone i n t h e

phase. The i n f l u e n c e o f a d d i t i o n o f a l a r g e l y s o l u b l e element i n t h e

phase such as aluminium c o n t r i b u t e s t o a s i q n i - f i c a n t s t r e n g t h e n i n g b u t reduces t h e k i n e t i c s o f p r e c i p i t a t i o n 131.

Analyses o f a l l o y heat t r e a t e d 28 days a t 673 K have been performed. Titanium and aluminium a r e detected as doubly charged ions w h i l e copper i s detected as s i n g l y anddoubly charged ions. The obtained compositions over 6 samples and 25 000 detec- t e d i o n s a r e given i n t a b l e 1 and compared t o t h e nominal values.

Table 1 Observed composition

0

Nominal composition

T i t a n i u m data agree w e l l w i t h t h e nominal composition whereas t h e copper l e v e l i s a l i t t l e b i t t o o low. However, few small copper r i c h zones w i t h sizes s m a l l e r than two nm were detected. Composition p r o f i l e s shown f i g u r e 4 e x h i b i t a w e l l r e s o l v e d Cu enriched r e g i o n t h e s i z e o f which i s about 1 nm and whose copper composition can be r o u g h l y estimated t o 25 a t %.

The observed l a c k o f copper can a c t u a l l y be explained i n two ways. On t h e one hand t h e volume f r a c t i o n o f GP zones i s low, atom probe data might be n o t r e p r e s e n t a t i v e o f t h e o v e r a l l composition. On t h e o t h e r hand some analyses may have been performed i n copper depleted zones near a g r a i n boundary, where a

89 0.2 88.8

1.75 0.1 2.3

9.25

O .2

8.9

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s o l u t e segregation i s known t o occur.

Fig. 4 - Composition p r o f i l e f o r a T i Cu A l sample showincj a copper enriched zone

Fig.

-

I

A u t o c o r r e l a t i o n f u n c t i o n f o r A l i n T i Cu Al a l l o y

An o t h e r i n t e r e s t i n g r e s u l t concerns aluminium ( f i g u r e 5 ) f o r which c o n c e n t r a t i o n f l u c t u a t i o n s between 5 and 15 a t % were observed w i t h a wavelength o f 400 ions ( i e 5 t o 6 nm).

Hydrosen

A l a r g e amount o f hydrogen ions was detected a t t h e beginning o f analyses o f

newly prepared specimens. F i g u r e 6 i l l u s t r a t e s t h i s phenomenon f o r a T i Al

sample. Although experimental c o n d i t i o n s ( p u l s e f r a c t i o n 0.2, r e p e t i t i o n r a t e

40 Hz, t i p temperature 50 K ) were h e l d constant, hydrogen was no l o n g e r received

a f t e r 1 000 t o 3 000 metal ions were detected ( f i g u r e 7 ) . The same r e s u l t was

obtained w i t h T i Cu Al samples ( f i g u r e 8).

Fig. 7 - composition p r o f i l e s f o r a freshly prepared Ti Al sample. The cumulative number of H , Al and Ti ions i s plotted versus the number of H + Al

Ti detected ions

Fig. 6 - Atom probe mass spectrum of a f reshly prepared Ti Al sample

Fig. 8 - Composition

p r o f i l e of hydrogen

f o r a new Ti Cu Al

sample

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Our i n t e r p r e t a t i o n i s t h a t t h e major p a r t o f t h e observed hydrogen was introduced i n - t o t h e specimen d u r i n g t h e e l e c t r o p o l i s h i n g . The contaminated depth v a r i e s from one

specimen t o another b u t l i e s between a few hundred h g s t r o m s and two thousand 8ngstr5ms. The p r o p o r t i o n o f hydrogen detected ions f o r t h e contaminated zone i s c o n s t a n t f o r each sample and can reach 60 a t %.

Acknowledgments

The study on t i t a n i u m base a l l o y s i s performed i n c o l l a b o r a t i o n w i t h t h e O f f i c e N a t i o n a l dlEtudes e t de Recherches Aérospatiales (O. N. E. R. A. - C h a t i l l o n ) . The authors thank Drs A. LOISEAU and A. VASSEL f o r t h e f r u i t f u l and s t i m u l a t i n g discussions.

REFERENCES

/1/ M a r t i n , C., B l a v e t t e , D., Sarrau, J. M., Rev. Phys. Appl., 19 (1984) 27 /2/ Loiseau, A., Lasalmonie, A., Acta Cryst., 839 (1983) 580

/3/ Vassel, A., 5 t h I n t e r n a t i o n a l Symposium on Titane, Münich (1983)