INTERNAL FRICTION AND MECHANICAL PROPERTIES OF NEW CERAMICS

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INTERNAL FRICTION AND MECHANICAL

PROPERTIES OF NEW CERAMICS

K. Matsushita, T. Okamoto, M. Shimada

To cite this version:

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INTERNAL FRICTION AND MECHANICAL PROPERTIES O F NEW CERAMICS

K. MATSUSHITA, T. OKAMOTO AND M. SHIMADA'

The I n s t i t u t e o f S c i e n t i f i c a n d I n d u s t r i a l R e s e a r c h , Osaka U n i v e r s i t y , I b a r a k i , Osaka 567, J a p a n + D e p a r t m e n t

of

A p p l i e d C h e m i s t r y , F a c u l t y

of

E n g i n e e r i n g , Tohoku U n i v e r s i t y , S e n d a i , Miyagi 980, J a p a n A b s t r n c t - S t r e s s a m p l i t u d e and t e m p e r a t u r e d e p e n d e n c e s of i n t e r - n a l f r i c t i o n i n p o l y c r y s t a l and s i n g l e c r y s t a l a l u m i n a s and a l u m i n a s s u b j e c t e d t o t h e r m a l s h o c k , were measured. M i c r o c r a c k s i n t r o d u c e d by w a t e r q u e n c h i n g were d e t e c t e d by i n t e r n a l f r i c t i o n measurement. An i n c r e a s e i n i n t e r n a l f r i c t i o n due t o s o f t e n i n g a t t h e g r a i n boundary i n t h e p o l y c r y s t a l a l u m i n a was o b s e r v e d above 600 C. The f l e x u r a l s t r e n g t h and t h e h a r d n e s s d e c r e a s e d w i t h i n c r e a s i n g i n t e r n a l f r i c t i o n . 1 . I n t r o d u c t i o n - Much a t t e n t i o n h a s r e c e n t l y been p a i d t o s t r u c t u r a l c e r a m i c s , s u c h a s a l u m i n a , s i l i c o n n i t r i d e , s i l i c o n c a r b i d e , and p a r t i a l l y s t a b i l i z e d z i r c o n i a , s e r v i c e a b l e a t e l e v a t e d t e m p e r a t u r e s -

.

I n s t a n t a n e o u s d e c r e a s e i n s t r e n g t h of a l u m i n a s u b j e c t e d t o t h e r m a l shock h a s been i n v e s t i g a t e d by ~ a s s e l m a n ~ ) r 5 ) . I n o r d e r t o examine t h e s t r e n g t h b e h a v i o r of b r i t t l e c e r a m i c s w i t h m i c r o c r a c k s , i n t e r n a l f r i c t i o n and Young's modulus a r e measured.

U s u a l l y , low m e l t i n g p o i n t compounds, s u c h a s SiO2 and MgO, a r e u s e d a s a s i n t e r i n g a d d i t i v e . The m e c h a n i c a l p r o p e r t i e s , s u c h a s s t r e n g t h , h a r d n e s s , and y o u n g ' s modulus, of t h e c e r a m i c s d e c r e a s e above t h e s o f t e n i n g t e m p e r a t u r e o f a s e c o n d p h a s e a t t h e g r a i n boundary. I f t h e m e c h a n i c a l p r o p e r t i e s of c e r a m i c s a r e d e t e r m i n e d by a n o n d e s t r u c t i v e t e s t , t h i s t e s t c a n be u t i l i z e d a s a s t r e n g t h test i n s t e a d of a d e s t r u c t i v e t e s t .

2 . E x p e r i m e n t a l P r o c e d u r e - The f l e x u r a l v i b r a t i o n method was u s e d f o r i n t e r n a l f r i c t i o n and y o u n g ' s modulus measurements a t a b o u t 2-5 KHz f r e q u e n c y . One end of t h e specimen was c o a t e d w i t h c a r b o n a s a n e l e c t r o d e . The specimen was v i b r a t e d by e l e c t r o s t a t i c f o r c e between t h e specimen and t h e d r i v e r . The s t r a i n a m p l i t u d e and t e m p e r a t u r e d e p e n d e n c e s of i n t e r n a l f r i c t i o n and Young's modulus a r e measured.

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C10-546 JOURNAL DE PHYSIQUE

The p o l y c r y s t a l s p e c i m e n u s e d i n t h e p r e s e n t s t u d y was p r e s s u r e - l e s s s i n t e r e d c o m m e r c i a l a l u m i n a (A-3997, Narumi China Co.) c o n t a i n - i n g 0.3%MgO, 0.01 % S i 0 2 a n d 0.06%CaO. The d e n s i t y was 3.929/cm3. The s i n g l e c r y s t a l specimen w a s a l s o u s e d and i t s l o n g i t u d i n a l d i r e c t i o n was p a r a l l e l t o t h e [ I 1 0 2 1 d i r e c t i o n . Thermal s h o c k t e s t were made by i c e - w a t e r - q u e n c h i n g t h e s p e c i m e n s a f t e r h e l d f o r a t l e a s t 30 min. i n a f u r n a c e m a i n t a i n e d a t p r e d e t e r m i n e d t e m p e r a t u r e s .

F l e x u r a l s t r e n g t h o f s p e c i m e n s was t e s t e d by a t h r e e p o i n t b e n d i n g method on a 80mm s p a n a t room t e m p e r a t u r e . Hot h a r d n e s s was measured

i n

vacuum u s i n g a m i c r o v i c k e r s tester.

3 . E x p e r i m e n t a l R e s u l t s - The f l e x u r a l s t r e n g t h (@+), Young's modulus ( E ) a n d i n t e r n a l f r i c t i o n ( Q - 1 ) a r e shown a s a f u n c t i o n of q u e n c h i n g t e m p e r a t u r e d i f f e r e n c e ( A T ) i n Fig.1. I * I D - @ - - @ 1 @ 1 non-quenched

*0°1

0'

I

104

105

106

10'

lo8

Stress Amplitude

O/

Pa

Fig. 1 Quenching temperature difference Fig. 2 S t r e s s amplitude dependence of

dependences of flexural strength i n t e r n a l f r i c t i o n i n quenched specimen.

(6f), Young's mcdulus (E) and i n t e r n a l AT condition are indicated i n

the

figure. f r i c t i o n (Q-I )

.

E and Q-1 -re

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modulus and i n t e r n a l f r i c t i o n of t h e non-quenched s p e c i m e n a r e a b o u t 275MPa, 370GPa and 0 . 3 x 1 0 - ~ , r e s p e c t i v e l y . The f a c t t h a t e a c h of t h e t h r e e v a l u e s k e p t c o n s t a n t up t o 200°C i n A T s u g g e s t e d t h a t t h e r e were no m i c r o c r a c k s i n t h e specimen. I n t h e t e m p e r a t u r e r a n g e 250 t o 3 0 0 t h e s t r e n g t h m a r k e d l y d e c r e a s e d d u e t o t h e n u c l e a t i o n o f ~ ~ ~

m i c r o c r a c k s a n d c r a c k p r o p a g a t i o n i n t h e specimen. C o r r e s p o n d i n g t o a n i n s t a n t a n e o u s d e c r e a s e i n s t r e n g t h , i n t e r n a l f r i c t i o n i n c r e a s e d from 0 . 3 ~ 1 0 - 3 t o 0 . 7 5 ~ 1 0 - 3 a n d Young's modulus d e c r e a s e d by a b o u t 6GPa. I n t h e q u e n c h i n g t e m p e r a t u r e r a n g e from 300 t o 400°C, t h e v a l u e of i n t e r n a l f r i c t i o n was c o n s t a n t . T h i s f a c t means t h a t t h e amount a n d s i z e of c r a c k s i n t h e s p e c i m e n quenched from 300°C w e r e a l m o s t t h e same a s t h o s e of 4 0 0 ' ~ . The s t r e s s a m p l i t u d e d e p e n d e n c e of i n t e r n a l f r i c t i o n i s shown i n F i g . 2 . When t h e A T was l e s s t h a n 2 0 0 t h e ~ ~ ~ stress d e p e n d e n c e o f i n t e r n a l f r i c t i o n was v e r y s m a l l . On t h e o t h e r h a n d , t h e i n t e r n a l f r i c t i o n i n a l u m i n a quenched from t h e t e m p e r a t u r e r a n g e from 300 t o 4 0 0 ' ~ i n c r e a s e d u n d e r s t r e s s a m p l i t u d e a b o v e a b o u t 3MPa. I t i s e x p e c t e d t h a t c r a c k s formed by q u e n c h i n g from 300

A

1°-'0 200 400 600 800 1000 1200 Temperature ('C) 8

-

0

b

-

6 C 0

.-

.w U

.-

t

-

4- 4

f

..

-

2 0

Fig.3 Temperature dependences of Fig.4 Temperature dependences of Vickers i n t e r n a l f r i c t i o n and Young's d u l u s hardness and internal f r i c t i o n i n poly i n p l y and single a l d n a crystal. and single alumina crystal.

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C10-548

JOURNAL

DE

PHYSIQUE

or 400°C were very small both in size and in amount. But the effect

of cracks on the strength was much greater than that on internal

friction because of the stress concentration at the end of cracks.

With increasing A T over 50O0c, strength and Young's modulus decreased

and internal friction increased gradually. This behaviour of stren-

gth, Young's modulus and internal friction in alumina should result

from the growth and combination of cracks.

Temperature dependences of internal friction and young's modulus

in polycrystal and single crystal aluminas are shown in Fig.3.

Young's modulus of the single crystal alumina decreased linearly with

increasing temperature and the temperature coefficient of Young's

modulus of the polycrystal alumina slightly decreased above 600

C.

Internal friction in the single crystal alumina increased monotonously

with increasing temperature. On the other hand, internal friction in

the polycrystal alumina markedly increased above 600

C.

Vickers

hardness and internal friction in the polycrystal and single crystal

aluminas are plotted against temperature on logarithmic scale in

Fig.4.

The Vickers hardness versus temperature plot for the polycry-

stal alumina could be divided into two lines, at 600 C.

The internal

friction versus temperature plot could be also divided

into

two lines at

600 C.

This inflection point, 600 C, has to be associated with grain

boundary characteristics. The polycrystal alumina contains MgO, CaO

and SiO2. These additives concentrate at the grain boundary.

Increase in internal friction and decrease in hardness above 600

C

should relate to the softening of these additives.

References

1 )

M.Shimada, K.Matsushita, S.Kuratani, T-Okamoto,

K-Koizumi,

K.Tsukuma and T.Tsukidate,

J.Am.Ceram.Soc.,~(1984),

23. 2) W.W.R.Kriege1

and H.Polmour, "~echanical

Properties of Engineering

Ceramics",(Interscience Publisher, New York, London, 1961

) .