PREPARATION OF SIC-WHISKER REINFORCED CVD-SIC

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PREPARATION OF SIC-WHISKER REINFORCED CVD-SIC

E. Fitzer, W. Remmele, G. Schoch

To cite this version:

E. Fitzer, W. Remmele, G. Schoch. PREPARATION OF SIC-WHISKER REINFORCED CVD-SIC.

Journal de Physique Colloques, 1989, 50 (C5), pp.C5-209-C5-217. �10.1051/jphyscol:1989527�. �jpa-

00229550�

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JOURNAL DE PHYSIQUE

Colloque C5, supplbment au n05, Tome

50,

mai 1989

PREPARATION OF SIC-WHISKER REINFORCED CVD-SIC E. FITZER, W. REMMELE and G. SCHOCH

Institut fiir Chemische Technick, Universitdt Karlsruhe, Kaiserstrasse

12, 0-7500

Karlsruhe

1,

F.R.G.

L'article decrit une etude experimentelle de la preparation des composites Sic renforces par des whiskers Sic par la dB- position de Sic de la phase vapour (CVD) et l'infiltration de la phase vapeur (CVI) utilisant le trichloromethylsilane

(H3CSiC13, MTS) c o m e precurseur Sic volatile. La procedure experimentelle est exprime par la temperature de dgposition, la pression totale, la composition du gaz porteur et par la concentration du MTS dans la phase gazeuse. Les rgsultats sont discutes par les changes de la masse, de la porosite et de la distribution de la grandeur des pores. Des micro- graphies electronigues par balayage sont presentees pour la description de la morphologie des couches d6posees. Des dates prealables sur les proprietes mechaniques sont prsenteees c o m e resistance

d

la flexure

d

la temperature ambiente. Les parmetres utilisables

d

obtenir des "all-Sic-Composites"

renforc&.s par des whiskers Sic avec une porosit& d'environ 25

vol-% sont discutes an detail.

Abstract

The paper describes an experimental study on the preparation ofSiC-whisker reinforced Sic-composites by Chemical Vapour Deposition (CVD) and Chemical Vapour Impregnation (CVI) with trichloromethylsilane as volatile Sic-precursor. The experi- mental procedure is described in terms of deposition tempera- ture, total pressure, carrier gas composition and content of the MTS (H CSiC1)-precursor in the gas phase. The results are discussed in terms of weight gain, change in porosity and pore size distribution. Scanning electron micrographs are presented for the description of the morphology of the deposits. Ten- tative values on the mechanical properties of selected samples are given as room temperature flexural strength data. The process parameters to achieve whisker reinforced "all SiC- composites" with about 25 vol-% remaining total porosity are described in detail.

1. Introduction

The main purpose of the present study is the preparation of B-Sic-whisker reinforced all Sic-composites by impregnation of Sic-whisker sheets without any temporary binder with a CVD-Sic-matrix.

Suitable CVI-conditions for the densification of commercially available reaction-bonded (RB-) Sic were elaborated previously

(2,3).

For the present substrate materials and the equipment used here, we had to modify the

CVT-

parameters to find a new optimum. Compared to former works the deposition temperatures were decreased to 900-1000

'C

in order to make sure that the overall reaction rate of the densification process remains reaction rate con- trolled. Some impregnation of RB-Sic-samples with high porosity were performed for comparison.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989527

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JOURNAL DE PHYSIQUE 2. E x p e r i m e n t a l

2.1 Sample m a t r i x

The R-Sic-whisker s h e e t s ( 4 0 x 5 ~ 3 mm i n s i z e ) were c a k e s from a vacuum f i l t r a - t i o n (500 mbar) of a s u s p e n s i o n o r t h e w h i s k e r s (TOKAMAX) i n butanone ( s e e t a b . 1 ) . The i n i t i a l open p o r o s i t y of t h e s e samples was a b u t 90 v o l - % .

The i n d u s t r i a l l y f a b r i c a t e d p o l y g r a n u l a r b u l k RB-Sic w i t h a mean g r a i n s i z e of a b o u t 0 . 8 pm had a t o t a l p o r o s i t y of 30 t o 50 v o l - % and p o r e e n t r a n c e s w i t h a r a d i u s 7 . 5 pm. A p o r e s i z e c h a r a c t e r i z a t i o n of t h e w h i s k e r s h e e t s by Hg- p o r o s i m e t r y c a n n o t be performed due t o t h e a b s e n c e o f a b i n d e r between t h e w h i s k e r s b e f o r e CVI-treatments.

2.2 Experimental P r o c e d u r e

The e x p e r i m e n t s were c a r r i e d o u t i n a r e s i s t a n c e - h e a t e d h o t w a l l a r r a n g e - ment. The samples were a r r a n g e d i n such a way, t h a t f r e e g a s f l o w around t h e

samples was g u a r a n t e e d . The d e p o s i t i o n t e m p e r a t u z e was v a r i e d between 900 and 1000 'C f o r t h e Sic-whisker s u b s t r a t e s . Hydrogen, Argon and m i x t u r e s of b o t h were u s e d a s c a r r i e r g a s . The t o t a l p r e s s u r e v a r i e d from 150 t o 500 mbar. A s v o l a t i l e p r e c u r s o r f o r t h e S i c - d e s p o s i t i o n T r i c h l o r o m e t h y l s i l a n e ( H CSiC1, MTS) w a s used. The vapour p r e s s u r e of t h e MTS was a d a p t e d i n such a way t h a t a s i l a n e - c o n t e n t of a b o u t 50 mole-% i n t h e g a s phase was o b t a i n e d i n a l l c a s e s . 2.3 C h a r a c t e r i z a t i o n of t h e impregnated samples

The i n f i l t r a t e d samples were c h a r a c t e r i z e d by t h e i r o x i d a t i o n b e h a v i o u r d u r i n g h e a t i n g up t o 1500 O C , X-ray a n a l y s i s , d e n s i t y , p o r o s i t y , p o r e s i z e d i - s t r i b u t i o n , by s c a n n i n g e l e c t r o n microscopy and by mechanical p r o p e r t i e s .

D e n s i t y and p o r o s i t y were d e t e r m i n e d by w a t e r a d s o r p t i o n

( a ) ,

and t h e p o r e s i z e d i s t r i b u t i o n was measured by Hg-porosimetry. From t h e b u l k d e n s i t y t h e c o r r e s p o n d i n g c l o s e d p o r o s i t y c a n be c a l c u l a t e d u s i n g t h e v a l u e s compiled i n Tab.2. The c o r r e l a t i o n of t h e v a l u e s f o r b u l k d e n s i t y and c l o s e d p o r o s i t y i s d e r i v e d under t h e p r e c o n d i t i o n of p o r e f r e e CVD-Sic w i t h a d e n s i t y of

3.215 g/cm, t h e same a s known f o r t h e s i n g l e c r y s t a l . S i n c e i t i s f r e q u e n t l y s t a t e d t h a t S i c - l a y e r s d e p o s i t e d a t highsilane-concentrations c o n t a i n c o n s i - d e r a b l e amounts of f r e e c a r b o n ( 1 , 4 , 5 , 6 ) , t h e v a l i d i t y of such assumption was c o n f i r m e d by s c a n n i n g e l e c t r o n m i c r o g r a p h s ( e . g . F i g . 8 ) , by w e i g h t change du- r i n g h e a t i n g up t o 1500 'C a t a h e a t i n g r a t e o f 10 K/min i n a t h e r m a l b a l a n c e and by X-ray-diffrActographs. These e x p e r i m e n t s gave no r e s u l t s t h a t a l l o w t h e c o n c l u s i o n t h a t f r e e c a r b o n was c o d e p o s i t e d .

An i n f o r m a t i o n a b o u t t h e e f f e c t i v e p o r e f i l l i n g by Sic-CV1 on one hand and p o r e b l o c k i n g mainly due t o S i c d e p o s i t i o n i n t h e s u r f a c e zone on t h e o t h e r i s o b t a i n e d from t h e c u r v e s o f t h e w e i g h t g a i n p e r t i m e . A b l o c k i n g of p o r e en- t r a n c e s and necks l e a s t o a r e d u c t i o n o f t h e s u r f a c e a r e a a c c e s s i b l e f o r CVD and t h e r e f o r e t o a c o n s i d e r a b l e d e c r e a s e o f t h e s l o p e of such a c u r v e . The f l e x u r a l s t r e n g t h of t h e Sic-whisker r e i n f o r c e d CVD-Sic w i t h a w h i s k e r c o n t e n t o f a b o u t 10 v o l - % was measured i n a t h r e e p o i n t bending t e s t a t room tempera- t u r e ( 7 ) u s i n g samples w i t h a s i z e o f 4 0 x 5 ~ 3 mm l / d - r a t i o of a b o u t 10 t o 1 5 ) . 3. R e s u l t s

3.1 The r a t i o between p o r e f i l l i n g and sample c o a t i n g by CVD

F i g . l a shows t h e w e i g h t g a i n by i m p r e g n a t i o n of Sic-whisker s h e e t s a t 900 OC w i t h a c o n s t a n t s i l a n e c o n c e n t r a t i o n of a b o u t 50 mole-%. The i n i t i a l w e i g h t g a i n i n d i c a t e s i n p o r e d e p o s i t i o n , whereas d e c r e a s e of t h e s l o p e i s e x p l a i n e d by r e d u c t i o n of t h e f r e e i n n e r s u r f a c e due t o b l o c k i n g of p o r e e n t r a n c e s and necks. For r e a c t i o n t i m e s blow 10 h i t c a n b e r e c o g n i z e d t h a t such b l o c k i n g d o e s n o t p l a y an i m p o r t a n t r o l e . A t 1000 OC t h e change of t h e s l o p e s o f t h e v a r i o u s c u r v e s i s s h i f t e d t o s h o r t e r CVI-periods ( s e e F i g . l b ) .

3.2 Bulk d e n s i t y and c l o s e d p o r o s i t y

The f o r m a t i o n of c r o s e d p o r o s i t y i s i n f l u e n c e d s t r o n g l y by t h e a p p l i e d c a r r i e r g a s c o m p o s i t i o n and t h e t o t a l p r e s s u r e a s c a n be s e e n from Tab.3. F o r p o l y g r a n u l a r RB-Sic 2 t o 5 v o l - % c l o s e d p o r o s i t y i s t h e b e s t i m p r e g n a t i o n r e - s u l t a f t e r 20 h ( T a b . 3 a ) . I n c a s e of hydrogen c a r r i e r g a s t h e l o w e s t p r e s s u r e

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(200 mbar) r e s u l t s i n t h e b e s t p o r e f i l l i n g what i s e x p e c t e d because t h e h i g h e r s i l a n e o f f e r i n t h e d e p o s i t i o n g a s w i l l s h i f t t h e mechanism i n t o t h e d i f f u s i o n c o n t r o l l e d a r e a . I n c a s e of Argon t h e d e g r e e of p o r e f i l l i n g i n - c r e a s e s w i t h i n c r e a s i n g t o t a l p r e s s u r e . That means, t h a t t h e r e a c t i o n r a t e r e - mains s m a l l e r t h a n t h e r a t e of mass t r a n s f e r even i n c a s e s of h i g h e r s i l a n e o f f e r s . The r e s u l t s o b t a i n e d f o r t h e m i x t u r e of Argon/70 v o l - % Hydrogen show t h a t t h e s u r f a c e r e a c t i o n r a t e - i s s t i l l lower t h a n t h a t of mass t r a n s f e r i n s p i t e of t h e Hydrogen c o n t e n t . A s shown b e f o r e , Hydrogen a c t s a s a r e a c t i v e r e a c t i o n component and n o t o n l y a s a c a r r i e r g a s . N e v e r t h e l e s s , t h e r e a c t i o n r a t e i s s i m i l a r a s i n p u r e Argon. We c a n c o n c l u d e f u r t h e r m o r e t h a t t h e r e can- n o t b e a c a t a l y t i c i n f l u e n c e of Hydrogen on t h e o v e r a l l r e a c t i o n .

The r e s u l t s o b t a i n e d f o r Sic-whisker s h e e t s a s s u b s t r a t e a r e compiled i n Tab.3b. A t 1000 OC t h e t r a n s i t i o n between r e a c t i o n and d i f f u s i o n c o n t r o l of t h e o v e r a l l p r o c e s s depends on t h e a p p l i e d t o t a l p r e s s u r e and o c c u r s a t a b o u t 350 mbar. Below 350 mbar t h e f o r m a t i o n of c l o s e d p o r e s i s reduced due t o t h e a c c e l e r a t i o n of d i f f u s i o n by a n i n c r e a s i n g c o n c e n t r a t i o n g r a d i e n t between t h e r e a c t i o n s i t e and t h e b u l k g a s p h a s e , above 350 mbar t h e o v e r a l l p r o c e s s be- comes d i f f u s i o n c o n t r o l l e d . A t 900 'C t h e r e a c t i o n r a t e i s c o n s i d e r a b l y s m a l l e r l e a d i n g t o a s m a l l e r amount of c l o s e d p o r o s i t y . T h i s i n d i c a t e s t h a t a t t h i s t e m p e r a t u r e t h e r a t e o f t h e o v e r a l l p r o c e s s i s c o n t r o l l e d by t h e r e a c t i o n con- s t a n t f o r a l l a p p l i e d p r e s s u r e s .

3.3 Open and t o t a l p o r o s i t y

I n F i g . 2 t h e open p o r o s i t y of Sic-whisker samples impregnated w i t h S i c i s shown a s f u n c t i o n o f t h e i n f i l t r a t i o n time. The open p o r o s i t y ( i n i t i a l l y r a n g i n g from a b o u t 85 t o 92 v o l - % )

-

t h e s e d a t a a r e d e r i v e d from t h e volume of t h e whisker c a k e s , d e n s i t y and mass o f t h e w h i s k e r s

-

i s reduced t o 15 to- 25 v o l - % . I t s h o u l d be reminded, t h a t t h e aim of t h e s t u d y i s t o keep t h e open p o r e s a s l o n g a s p o s s i b l e a c c e s s i b l e f o r d e p o s i t i o n i n o r d e r t o f i l l t h e p o r e s a s c o m p l e t e l y a s p o s s i b l e . A s e x p e c t e d , t h e open p o r o s i t y a f t e r t h e same i n - f i l t r a t i o n t i m e remains h i g h e r a t 900 OC t h a n a t 1000 'C. F i g . 3 shows c u r v e s f o r t h e t o t a l p o r o s i t y w i t h a minimum a t a b o u t 20 v o l - % . A t 900 " C t h e t o t a l p o r o s i t y can b e reduced f u r t h e r m o r e even a f t e r 20 h of i m p r e g n a t i o n . A t a de- p o s i t i o n t e m p e r a t u r e of 1000 'C t h e minimum f i n a l t o t a l p o r o s i t y of a b o u t

35 v o l - % i s a c h i e v e d a f t e r 5 h a l r e a d y and n o s i g n i f i c a n t f u r t h e r d e c r e a s e o f t h e t o t a l p o r o s i t y i s o b s e r v e d . P l e a s e , keep i n mind, t h a t a l l d a t a on p o r o s i - t y h e r e r e f e r t o a sample t h i c k n e s s of 3 mm, t h a t means a n i m p r e g n a t i o n d e p t h of 1 . 5 mm.

3.4 R e s u l t s of Hg-porosimetry

The p o r e r a d i i d i s t r i b u t i o n of t h e open p o r o s i t y of s e l e c t e d samples was examined by Hg-porosimetry. The r e s u l t s a r e g i v e n i n F i g . 4 f o r p o l y g r a n u l a r RB-Sic and i n F i g . 5 f o r Sic-whisker r e i n f o r c e d CVD-Sic. I n a l l c a s e s , t h e p o r e r a d i i d e c r e a s e w i t h i n c r e a s i n g d e p o s i t i o n t i m e ( F i g . 4 a ) , d e c r e a s i n g t o t a l p r e s - s u r e ( F i g . 4b) and d e c r e a s i n g Hydrogen-content i n t h e c a r r i e r g a s ( F i g . 4 c )

.

The c u r v e s of F i g . 5 show t h a t i n Sic-whisker r e i n f o r c e d CVD-Sic c o m p o s i t e s t h e p o r e r a d i i a r e c o n s i d e r a b l y s m a l l e r and b a s i c a l l y show t h e same tendency a s t h o s e measured f o r p o l y g r a n u l a r RE-Sic. As shown i n F i g . 5 f o r a l l combina- t i o n s of p a r a m e t e r s p o r e s w i t h r a d i i 500 nm c a n n o t b e f i l l e d ( F i g s . 5 , 6 ) .

3.5 Scanning e l e c t r o n microscopy

F i g . 7 shows t h e morphology of t h e s u r f a c e d e p o s i t e s . The n o d u l a r s t r u c t u r e i s t y p i c a l f o r a l l samples i n d e p e n d e n t from t y p e of s u b s t r a t e and d e p o s i t i o n c o n d i t i o n s .

Fig.8 shows t h e c r o s s s e c t i o n s of samples i n f i l t r a t e d w i t h S i c f o r 15 h . The t r a n s i t i o n from t h e s u r f a c e t o t h e i n i t i a l b u l k of t h e sample i s shown.

The samples impregnated a t t h e h i g h t e m p e r a t u r e s have a v e r y dense s u r f a c e w i t h a r e l a t i v e l y porous s t r u c t u r e below, t y p i c a l f o r a d i f f u s i o n c o n t r o l l e d o v e r a l l r e a c t i o n r a t e . A t lower t e m p e r a t u r e s such a s h a r p l i m i t between s u r - f a c e and i n n e r zone c a n n o t be o b s e r v e d , a l t h o u g h under t h e s e c o n d i t i o n s a g r a - d i e n t i n p o r o s i t y can be r e c o g n i z e d .

F i g . 9 a shows a r e l a t i v e l y r a r e s i t u a t i o n i n which a p o r e was c l o s e d a f t e r a s h o r t i n f i l t r a t i o n t i m e a l r e a d y . N e v e r t h e l e s s , b r i d g e bonding between t h e w h i s k e r s h a s a l r e a d y r a k e n p l a c e . F i g . 9 b shows t h e u s u a l s i t u a t i o n i n which a

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C5-212 JOURNAL

DE

PHYSIQUE

r e l a t i v e l y d e n s e m a t r i x i s formed p r i o r t o p o r e c l o s u r e . 3.6 T e n t a t i v e r e s u l t s on mechanical p r o p e r k i e s

For s e l e c t e d samples t h e mechanical p r o p e r t i e s a r e g i v e n i n Fig.10. The c u r v e shows t h a t t h e r e i s a maximum i n f l e x u r a l s t r e n g t h a t a b o u t 340 MPa f o r an open p o r o s i t y of a b o u t 5 v o l - % b e s i d e o f 20 v o l - % c l o s e d p o r o s i t y .

F i r s t r e s u l t s w i t h l o n g c a r b o n f i b r e s TORAY T800 show a . s i m i l a r b e h a v i o u r o f t h e f l e x u r a l s t r e n g t h when p l o t t e d v e r s u s t h e open p o r o s i t y .

4. Summary

The work r e p o r t e d h e r e h a s shown t h a t i n t h e whole r a n g e o f p a r a m e t e r s of d e p o s i t i o n t e m p e r a t u r e , t o t a l p r e s s u r e and c a r r i e r g a s composition a s s e l e c t e d h e r e S i c c a n be d e p o s i t e d from MTS i n t h e p o r e s o f p o r o u s b r i c k s i f t h e p o r e r a d i i exceed a b o u t 500 nm. I t i s shown f u r t h e r m o r e t h a t w h i s k e r r e i n f o r c e d

" a l l - S i c - c o m p o s i t e s " c a n b e p r e p r a r e d from whisker s h e e t s p r e p a r e d by f i l t r a - t i o n o f a s u i t a b l e s u s p e n s i o n w i t h o u t a p r i m a r y b i n d e r .

F o r t h e f i n a l s t r e n g t h an open p o r o s i t y of a b o u t 5 v o l - % seems t o be optimum;

a l e x u r a l s t r e n g t h o f 340 MPa h a s been o b t a i n e d . C o n d i t i o n s a r e shown under which t h e i n i t i a l t o t a l p o r o s i t y of a b o u t 90 v o l - % i s reduced t o 25 vol-% a s minimum.

Argon c a r r i e r g a s h e l p s t o m a i n t a i n a r e a c t i o n r a t e c o n t r o l even a t 1000 'C up t o a t o t a l p r e s s u r e of 350 mbar whereas i n Hydrogen c a r r i e r g a s t h e p o r e en- t r a n c e s a r e a l r e a d y blocked a f t e r 5 h o u r s .

Acknowledgement

The a u t h o r s wish t o e x p r e s s t h e i r t h a n k s t o t h e German Research Foundation f o r t h e f i n a n c i a l s u p p o r t f o r t h i s work.

5. R e f e r e n c e s

M. Bonnke, T h e s i s , U n i v e r s i t y o f K a r l s r u h e , 1965 D. Hegen, T h e s i s , U n i v e r s i t y of K a r l s r u h e , 1979 H . J . B u h l e r , T h e s i s , U n i v e r s i t y of K a r l s r u h e , 1976 R. ,Naslain e t a l . , Advances i n Cop. Mat. Vo1.2, pp. 1084-1097, P a r i s , 1980

R. N a s l a i n , F. L a n g l a i s i n " T a i l o r i n g M u l t i p h a s e Comp, Cer. Mat. Sc.Res.

( R . E . T r e s s l e r e t a l . e d s ) Vo1.20, pp. 145-164 Plenum P r e s s , New York, 1986

R. N a s l a i n and coworkers, P e r s o n a l communication, 1988/89 D I N 53457 (Measurement of mechanical p r o p e r t i e s ) , 1981

D I N 51918 (Measurement of d e n s i t i e s by w a t e r d e s o r p t i o n ) , 1986 E. F i t z e r , Proc. of I n t . Sympos. of F a c t o r s i n D e n s i f i c a t i o n and S i n t e r i n g of Oxide and Non-oxide Ceramics, 1978, J a p a n ,

pp. 618-673

P r o d u c t i n f o r m a t i o n by TOKAI Carbon Co., 1987

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T a b l e s and F i g u r e s T a b l e 1 : C h a r a c t e r i s t i c s of t h e R-Sic-whiskers ( 1 0

Diameter : 0 . 1

-

1 . 0 pm ( p r e d o m i n a n t l y 0 . 2

-

0 . 5 pm)

Length: 5 0

-

^{2 0 0}^pm

D e n s i t y : 3 . 1 7 g/cm

Heat r e s i s t e n c e : 1 6 0 0 'C i n a i r T e n s i l e s t r e n g t h : 3 0 0 0

-

1 4 0 0 0 MPa Young's modulus: 4 0 0

-

^{7 0 0}^GPa

...

Table 2 : Closed p o r o s i t y a s c a l c u l a t e d from b u l k d e n s i t y measurements

...

Bulk d e n s i t y

(g/cm) 3 . 2 1 5 3.054 2.984 2.733 2.572 2 . 4 1 1

c l o s e d p o r o s i t y ( - )

Table 3: Closed p o r o s i t y ( - ) of p o l y g r a n u l a r RB-Sic i n f i l t r a t e d a t 1 0 0 0 'C ( a ) and Sic-whisker s h e e t s i n f i l t r a t e d a t 9 0 0 and 1 0 0 0 'C i n Hydrogen- atmosphere r e s p e c t i v e l y (b)

( a ) ~ ~( h ) ~ - t ~ i ~ ~

...

X ( H a ) ~ ( t o t )

-

^(mbar) ⁰ ⁵ ^{1 0} ^{1 5} ^{2 0}

( b )

c v l - t h e

^{( h )} ^-r,

...

Temp. ~ ( t o t ) 0 5 1 0 1 5 2 0

( " C )

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C5-214 JOURNAL DE PHYSIQUE

9 -Total pressure :

- . . l 0 0 " b a r Int,llr0l#bn lemperatute- 988 O C -.-OS 200 nbar

- - o - 3 0 0 .bar g- --- - - - _- _-_-3

? .- ^L-

a)

XlH21il

I I

5 18 15

l n f i l t r a t i a n t ~ m e ( h ]

1

5 I 0 15 20

l n f i l t r o t i a n t i m e I h I

F i g . ? : R e l a t i v e w e i g h t g a i n o f w h i s k e r s h e e t s made a t d i f f e r e n t d e p o s i t i o n t e m p e r a t u r e s

1 hftltmlmn tmpmlun= 988 Q C

Told PSWI

-

..

¹⁰⁰^.b.,

-... 0- 288 .bar

--- ^{0 -}380 .b.,

-

_, _{. 6 8}

h

.- L _" .*--

. 1 0

---

^-0

g

^---a

a

0 1 l l

8 5 10 15 28

Infiltration tlme I h1

, C l 2.1?*1 I

0 I I I I

0 5 I 0 l 5 28

,C, 111222 1 I n f i l t r a t i o n t ~ m e ( h 1

F i g . 3 : T o t a l p o r o s i t y of Sic-whisker r e i n f o r c e d SIC p r e p a r e d a t 900 'C ( a ) and a t 1000 OC (b) r e s p e c t i v e l y

0 I

0 5 l 8 15 28

.-

^>o,2., l n f c i t r a t i o n time f h l

I I

B 5 1 8 15 1 0

' m I n f i l t r a t i o n tlme L h l

F i g . 2 : Open p o r o s i t y o f SiC- w h i s k e r r e i n f o r c e d S i c p r e p a r e d a t d i f f e r e n t d e p o s i t i o n t e m p e r a t u r e s

'"l,ll..tl." l,". . I,. X," t,.,

I " ( . l l t S l l O . l... . ^I.* , . ^21.

.,..

F i g . 4 : Pore r a d i i d i s t r i b u t i o n s of Sic-samples i n f i l t r a t e d . w i t h S i c under v a r y i n g e x p e r i - m e n t a l c o n d i t i o n s

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I"+lll..tl." _lap,,,n,,,tra,,.n 1 ...a P,.'."..: l".. l,..

.

^I..

-

^I^{' C}^*

5 *.an 2s.e > m e

Pore cad,"% , " - m

In,lltrall." I ..p. r.,"..

.

^I,,^'L

1 lnll,tnllon I,"

.

^{I . h}

**I ,,.l%",.:

- 111 1.I _.b..

.b..

100 .b..

S 5 , a , a I,..

," ., ,, POIP r a d l ~ s ln.1

Fig.5: Pore radii distribution of Sic-whisker samples impregnated with Sic

I n f i l t r a t i o n time = 5 h T o t a l pressure = 300 m b a r I n f i l t r a t i o n temperature :

----

p

l000 O C

900 OC

W

E 6 0 -

2 0 >

a 0

20 -

I

0 S00 l000 1500 2000

1 0 .?01.,30 Pore r a d i u s ^{l n m l}

Fig.6: Influence of the deposition temperature

on the pore radii distribution of SiC-

whisker samples impregnated with Sic

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JOURNAL DE PHYSIQUE

Fig.7: Surface of Sic-whisker samples Fig.8: Fracture surfaces of SiC- impregnated with Sic whisker samples impregnated

(1000 OC, 250 mbar in H2) with Sic for 15 h at a total for 5 h (a) and 15 h (b) pressure of 200 mbar in H2

at 800 (a), 900 (b) and l000 "C (c)

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Fig. 9: Details of the fracture surf ace of Sic-whisker reinforced Sic

Fig.10: Flexural strength of Sic-whisker reinforced CVD-Sic as a function of open porosity

350 -

S u b s t r a t e :

TOKAMAX- Sic-Whiskers W h i s k e r - c o n t e x t = 10 Vol.%

C l o s e d p o r o s i t y = 2 0 V o l % M a t r i x C V O - S I C

3 X

3 50- L L

I

10 20 30 40 50 60

Open porosity ( V o l . % ) I C T 203231