DEFORMATION OF Al2O3 SINGLE CRYSTALS BETWEEN 25°C AND 1800°C : BASAL AND PRISMATIC SLIP

HAL Id: jpa-00220695

https://hal.archives-ouvertes.fr/jpa-00220695

Submitted on 1 Jan 1981

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

DEFORMATION OF Al2O3 SINGLE CRYSTALS

BETWEEN 25°C AND 1800°C : BASAL AND

PRISMATIC SLIP

J. Castaing, J. Cadoz, S. Kirby

To cite this version:

DEFORMATION OF A 1203 SINGLE CRYSTALS BETWEEN 25°C AND 1800°C : BASAL AND PRISMATIC SLIP (*)

J. Castaing, J. Cadoz and S.H. Kirby#

Laboratoire de Physique des Matériaux, C.N.R.S.-Bellevue, 92190 Meudon, France •U.S. Geologiaal Survey, Mail Stop 77, 345 Middlefield Road, Menlo Park, California 94025, U.S.A.

Résumé.- Des essais de compression à vitesse constante ont été exécutés sur des monocristaux d'alumine entre 25°C et 1800°C sous une pression hydrosta-tique de 1500 MPa. Les cristaux sollicités pour le glissement prismahydrosta-tique se fracturent en-dessous de 200°C et pour le glissement basai en-dessous de 600°C. Les scissions critiques pour les 2 glissements ont été trouvées entre 100 MPa et 3000 MPa. Elles s'accordent avec l'extrapolation que l'on peut faire des résultats obtenus à haute température et pression normale. A b s t r a c t . - Compression t e s t s on alumina single c r y s t a l s have been performed under 1500 MPa h y d r o s t a t i c pressure a t temperatures between 25°C and 1800°C Specimens tested for prismatic s l i p failed below 200°C and those for basal s l i p below 600°C. C r i t i c a l resolved shear s t r e s s e s for both s l i p systems, have been in the range 100 MPa - 3000 MPa. They show a reasonable agreement with extrapolated values from high temperature-room pressure data.

1 . I n t r o d u c t i o n . - The m e c h a n i c a l p r o p e r t i e s o f Al-O., s i n g l e c r y s t a l s h a v e b e e n s t u d i e d f o r a l o n g t i m e ( f o r r e v i e w s , s e e / l , 2 / . C o n s t a n t s t r a i n r a t e c o m p r e s s i o n a t t e m p e r a t u r e s a b o v e 1100°C l e a d s t o p l a s t i c d e f o r m a t i o n . Below 1 1 0 0 ° C , c r y s t a l s show b r i t t l e f r a c t u r e f o r a l l o r i e n -t a -t i o n s o f -t h e s -t r e s s . I n o r d e r -t o s u p p r e s s f r a c -t u r e we h a v e u n d e r -t a k e n e x p e r i m e n t s a t h i g h h y d r o s t a t i c p r e s s u r e a n d a t t e m p e r a t u r e s b e t w e e n 20 a n d 9 5 0 ° C . F o r c o m p r e s s i o n p e r p e n d i c u l a r t o [ 0 0 0 1 ] p l a s t i c d e f o r m a -t i o n was a c h i e v e d a -t -t e m p e r a -t u r e s a s low a s 200°C / 3 / . We h a v e a l s o p e r f o r m e d c o m p r e s s i o n t e s t s t o a c t i v a t e t h e b a s a l s l i p , i . e . , w i t h t h e s t r e s s a t 45° t o t h e <1120> a n d [ 0 0 0 l ] d i r e c t i o n s , g i v i n g a Schmid f a c t o r o f 0 . 5 . T h i s o r i e n t a t i o n i s a l s o s u i t a b l e f o r t w i n n i n g / 4 / ; we h a v e how-e v how-e r , o b s how-e r v how-e d how-e x t how-e n s i v how-e b a s a l s l i p a b o v how-e 6 0 0 ° C . 2 . E x p e r i m e n t a l t e c h n i q u e s . - The e x p e r i m e n t a l t e c h n i q u e s h a v e a l r e a d y b e e n d e s c r i b e d i n p r e v i o u s p u b l i c a t i o n s / 3 , 5 / . S i n g l e c r y s t a l A 1 , 0 , ( ' ) z J was grown by t h e V e r n e u i l t e c h n i q u e . T h e y w e r e c u t i n t o p a r a l l e l e p i -3 &#-34; p e d s o f d i m e n s i o n s 2 x 2 x 5 mm f o r h i g h t e m p e r a t u r e t e s t s / 5 / a n d

__

Work performed while J. Castaing was at the U.S. Geological Survey with the Financial support of the A.T.P. - C.N.R.S./N.S.F. INT/N" 1993

Provided by Centre de Recherches de Grenoble Ugine-Kuhlman, 38560 Jarrie, France.

c3-44 JOURNAL DE PHYSIQUE

3.8 x 3.8 x 8.9 mm3 f o r low t e m p e r a t u r e t e s t s /3/. Two o r i e n t a t i o n s have been chosen i n o r d e r t o a c h i e v e maximum s h e a r s t r e s s f o r b a s a l s l i p and f o r p r i s m a t i c s l i p . Specimens f o r b a s a l s l i p were m e c h a n i c a l l y p o l i s h e d i n o r d e r t o a v o i d t w i n n i n g . A s c u t specimens were g e n e r a l l y used f o r p r i s m a t i c s l i p . A t t e m p e r a t u r e s above llOO°C, compression t e s t s were performed a t a t m o s p h e r i c p r e s s u r e i n a n I n s t r o n machine a t a c o n s t a n t s t r a i n r a t e = 1 . 3

x

1 0 - ~ s - l /5/

Below 950°C, compression t e s t s were performed under h y d r o s t a t i c p r e s s u r e o f 1500 MPa o b t a i n e d i n

a

NaCl s o l i d c o n f i n i n g medium /3/.

-5 -1

A c o n s t a n t s t r a i n r a t e

E

=

2

x

10 s was used. From s t r e s s - s t r a i n c u r v e s , v a l u e s f o r t h e f a i l u r e s t r e s s o r f o r t h e c r i t i c a l r e s o l v e d s h e a r s t r e s s c o u l d be deduced.

3. R e s u l t s and d i s c u s s i o n . - 3.1. g r a c t u r e . - Specimens deformed a t atmos- p h e r i c p r e s s u r e i n v a r i a b l y b r o k e below 1300°C f o r b a s a l s l i p and 1400°C f o r p r i s m a t i c s l i p a t a p p l i e d u n i a x i a l s t r e s s e s o f a b o u t 60 MPa and 220 MPa r e s p e c t i v e l y . The u n i a x i a l f r a c t u r e s t r e n g t h o f alumina a t room

I ~ l 1 1 1 1 1 1 1 1 1 1 1 1 -

Z.

MPa

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

\

I

*.

.

- \ , p r i s m a t i c

,

.

-

i

'.

-

-

-

100

-

-

-

4

-

_'.

A b a s a l \

9

-

4 ,

lo

\ ,

100 600 800 1000 1100

TOC\?

-

~ ~ l l l l i l l l l

-

l l ,

-

Fig. 1.- Critical resolved shear stress vs. temperature for basal and prismatic s l i p .

A t T > 1100°~, data were obtained a t atmospheric pressure. A t T < 950°c, they were obtained under 1500 MPa confining pressure (experimntal error on T:+ 50 MPa 131. For basal s l i p a t 950°c, the uncertainty in temperature i s due t o a failure of ther- mocouple.

Open symbols: our results.

t o [ 0 0 0 1 ] a x i s / 8 / . Up t o 1000°C, i n c r e a s i n g t e m p e r a t u r e r e d u c e s t h e f a i l u r e s t r e s s by a maximum f a c t o r o f 2 /9/. T h i s g i v e s v a l u e s n o t t o o much l a r g e r t h a n o u r s . The d i v e r g e n c e can e a s i l y b e e x p l a i n e d by d i f f e - r e n c e s i n t e s t geometry, c r y s t a l o r i e n t a t i o n o r s u r f a c e c o n d i t i o n s .

B e t t e r c a r e i n specimen p r e p a r a t i o n and f i t i n t h e compression j i g p e r - m i t t o i n c r e a s e t h e f a i l u r e s t r e s s o f specimens, hence t o d e c r e a s e t h e t e m p e r a t u r e o f t h e b r i t t l e - d u c t i l e t r a n s i t i o n . T h i s h a s been a c h i e v e d o n l y f o r b a s a l s l i p where t h e p l a s t i c i t y c o u l d b e e x t e n d e d down t o llOO°C ( F i g . 1 ) by p r e d e f o r m a t i o n above 1300°C.

The u s e o f a 1500 MPa h y d r o s t a t i c p r e s s u r e p e r m i t t e d u s t o e x t e n d t h e p l a s t i c i t y down t o 600°C f o r b a s a l s l i p and t o 200°Cfor p r i s m a t i c s l i p . For t h e former specimens, f a i l u r e o c c u r r e d a t a p p l i e d s t r e s s o f a b o u t 3600 MPa ( 3 t e s t s ) a l o n g a b a s a l p l a n e , r e s u l t i n g i n a n a p p e a r a n c e of c l e a v e d s u r f a c e . A f t e r compression a t room t e m p e r a t u r e , p r i s m a t i c s l i p o r i e n t e d specimens were t r a n s p a r e n t a t one end and opaque a t t h e o t h e r end ( P i g . 2 ) , a f e a t u r e which can b e a t t r i b u t e d t o m i c r o c r a c k i n g g i v i n g a n a p p a r e n t p l a s t i c deformation/3/. T h i s i s v e r y s i m i l a r t o what h a s been o b s e r v e d i n - s i t u d u r i n g h i g h p r e s s u r e , room t e m p e r a t u r e com- p r e s s i o n o f MgO p o l y c r y s t a l s

/ l o / .

Specimens o r i e n t e d f o r p r i s m a t i c s l i p and campressed below 200°C always f a i l e d a t s t r e s s e s o f a b o u t 6300 Mpa

( 5 t e s t s ) ; t h e f a i l u r e p l a n e s d i d n o t have low i n d e x c r y s t a l l o g r a p h i e o r i e n t a t i o n ( F i g . 2 ) . The f r a c t u r e s t r e n g t h s t h a t we measured under hy- d r o s t a t i c p r e s s u r e a r e i n r e a s o n a b l e agreement w i t h t h e v a l u e s f o r p o l y - c r y s t a l s o b t a i n e d from b i a x i a l compressive t e s t s /6/ o r c a r e f u l u n i a x i a l compression /7/.

c3-46

JOURNAL DE PHYSIQUE

A few c r a c k s a r e v i s i b l e on f i g u r e 2 which a r e p e r p e n d i x u l a r t o t h e c o m p r e s s i o r ~ a x i s . They have sometimes been s e e n i n specimens d e f o r - med a t h i g h e r t e m p e r a t u r e ( F i g . 3 ) . ,These c r a c k s a r e c a u s e d by t e n s i l e s t r e s s e s which a r i s e d u r i n g u n l o a d i n g , c o o l i n g and/or d e p r e s s u r i z a t i o n . They s t e m from d i f f e r e n c e s i n t h e e l a s t i c p r o p e r t i e s o f t h e specimen, and t h e e l e m e n t s o f t h e s o l i d c o n f i n i n g medium a s s e & l y /3/. Slow un- l o a d i n g and d e p r e s s u r i z a t i o n a t t h e t e s t t e m p e r a t u r e a l l o w f r i c t i o n a l and v i s c o u s r e l a x a t i o n of s t r e s s h e t e r o g e n e i t i e s due t o e l a s t i c m i s - matches; no c r a c k s a r e t h e n o b s e r v e d . F i g . 3 . - Transmission o p t i c a l micrograph of a t h i n s e c t i o n c u t p a r a l l e l t o (0001) p l a n e of an A1203 specimen o r i e n t e d f o r p r i s m a t i c s l i p : p = 1500 MPa,

T = 800°C, E = 3.2%. The whole specimen i s shown. Observation made between c r o s s e d p o l a r i z i n g f i l t e r s r e p e a l i n g s t r e s s b i r e f r i n g e n t bands p a r a l l e l t o

(1210).

3.2. P l a s t i c d e f o r m a t i o n . - P l a s t i c d e f o r m a t i o n h a s been a c h i e v e d be- low 950°C b o t h f o r b a s a l and p r i s m a t i c s l i p p r o v i d e d t h e c r y s t a l s a r e p r e s s u r i z e d d u r i n g t h e t e s t . The e a s i e s t way t o check t h a t s l i p h a s o c c u r r e d i s t o o b s e r v e t h i n s e c t i o n s o f t h e specimens between c r o s s e d p o l a r i z i n g f i l t e r s . They show b i r e f r i n g e n t bands which a r e t y p i c a l o f p r i s m a t i c s l i p ( F i g . 3 ) . O t h e r o b s e r v a t i o n s have been p u b l i s h e d /3/ which show t h a t <

1070

>

{ 1210 p r i s m a t i c s l i p h a s been a c t i v a t e d down t o 200°C.

The m i c r o s t r u c t u r e o f specimens o r i e n t e d f o r b a s a l s l i p i s l e s s c l e a r t h a n t h e one shown i n f i g u r e 3. S l i p bands a r e mixed w i t h t w i n s formed d u r i n g t h e i n i t i a l l o a d i n g o f t h e c r y s t a l s . The o r i e n t a t i o n chosen f o r t h e specimen i s v e r y f a v o u r a b l e f o r t w i n n i n g on two s y s t e m s

p e r a t u r e , h i g h p r e s s u r e and h i g h t e m p e r a t u r e , room p r e s s u r e . The two s e t s o f r e s u l t s seem t o f i t f o r p r i s m a t i c s l i p and h a s been d e s c r i b e d by a l i n e a r r e l a t i o n s h i p between l n r and T ( P i g . 1) /3/. I t might b e t h e same f o r b a s a l s l i p on a wide r a n g e o f t e m p e r a t ~ r e ~ e x c e p t t h a t t h e low t e m p e r a t u r e d a t a a r e t r a n s l a t e d upwards ( F i g . 1 ) . The h a r d e n i n g o b s e r v e d w i t h t h e b a s a l specimens i s p e r h a p s due t o t h e h i g h d e n s i t y o f t w i n s e x i s t i n g p r i o r t o b a s a l s l i p . A l i n e a r r e l a t i o n s h i p between l n ~ and TI (where

r

i s t h e c r i t i c a l r e s o l v e d s h e a r s t r e s s )

i s

r a t h e r n o v e l . However, it h a s been found f o r t h e v a r i a t i o n o f t h e s t r e s s a t t h e o n s e t o f s t a g e I11 f o r t h e d e f o r m a t i o n o f f . c . c . m e t a l s which i s c o n t r o l l e d by t h e c r o s s - s l i p of d i s l o c a t n o n s /12/. I t i s n o t c l e a r i f s u c h a mechanism i s r e l e v a n t t o s l i p i n alumina.

Acknowledgments.- The a u t h o r s a r e i n d e b t e d t o T. M i t c h e l l f o r sugges- t i n g t h e comparison w i t h s t a g e 111 i n f . c . c . m e t a l s .

/1/ B r e t h e a u , T., C a s t a i n g , J . , R a b i e r , J . and V e y s s i e r e , P . , Adv.Phys. (1979) 335

/2/ Kotchick, D . M . and T r e s s l e r , X . E . , J Am. Ceram. Soc. 63 (1900) 429

-

/3/ C a s t a i n g , J . , Cadoz, J . and Krrby, S.H., J. Am. Ceram. Soc., t o b e p u b l i s h e d

/ 4 / S c o t t , W . D . , i n "Deformation o f ceramic m a t e r i a l s " , R.C. B r a d t and R . E . T r e s s l e r , e d s . , ( P l e n u m P u b l . Co. New York)

1975, p. 151

/ 5 / Cadoz,

J.,

& s t a i n g , J . and P h i l i b e r t , J . , s u b m i t t e d f o r p u b l i c a t i o n i n Revue Phys. Appl.

/6/ Adams, PI. and S i n e s , G . , J . Am. Ceram. Soc.

2

(1976) 300 /7/ Lankford,

J . ,

J . Mater. S c i .

12

(1977)791.

/8/ Wachtman, J . B . J r . and Plaxwell, L.H., J . Am. Ceram. Soc. 42 (1959) 432

-

/9/ Wiederhorn, S.M., Hockey, B . J . and X o b e r t s , D . E . , P h i l o s . Mag. (1973) 783

/ l o /

Auten, T.A. and Radcliffe,S.V.,J.Am. Ceram. Soc.

2

(1976) 249

/11/ L a g e r l o f , P., Case Western Reserve U n i v e r s i t y , u n p u b l i s h e d r e s u l t

/12/ Haasen, P., P h y s i c a l M e t a l l u r g y , (Cambridge Univ. P r e s s , Cambridge) 1978, p. 278