SINTERING AND FRACTURE BEHAVIOR OF COMPOSITES BASED ON ALUMINA-ZIRCONIA (YTTRIA)-NONOXIDES

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SINTERING AND FRACTURE BEHAVIOR OF COMPOSITES BASED ON ALUMINA-ZIRCONIA

(YTTRIA)-NONOXIDES

T. Sato, A. Shiratori, M. Shimada

To cite this version:

T. Sato, A. Shiratori, M. Shimada. SINTERING AND FRACTURE BEHAVIOR OF COMPOSITES

BASED ON ALUMINA-ZIRCONIA (YTTRIA)-NONOXIDES. Journal de Physique Colloques, 1986,

47 (C1), pp.C1-733-C1-737. �10.1051/jphyscol:19861111�. �jpa-00225507�

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SINTERING AND FRACTURE BEHAVIOR OF COMPOSITES BASED ON ALUMINA-ZIRCONIA(YTTR1A)-NONOXIDES

T. SATO, A. SHIRATORI and M. SHIMADA

Department of Applied Chemistry, Faculty of Engineering, ~ o h o k u University, Sendai, 980. Japan

Rdsum6

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La r d s i s t a n c e 3 l a r u p t u r e e t l a t 6 n a c i t 6 des c6ramiques 1 base d'alumine e s t renforcdes p a r a j o u t de ZrOz(Y20,) e t de matdriaux monoxydes t e l s que S i c , Tic, TiN e t B4C. Un renforcement e t un durcissement importants s o n t a i n s i obtenus dans *es composites A1203-ZrO,-SiC e t A l , o , - z f l , - ~ i C . Abstract

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S t r e n g t h and toughness of A l 2 O 3 based ceramics were improved by d i s p e r s i n g ZrO,(Y,O,) and nonoxide m a t e r i a l s such a s S i c , Tic, TiN and B&.

S i g n i f i c a n t toughening and hardening were a t t a i n e d i n A1203-Zr0,-Sic and Al,O,-Zr0,-Tic composites.

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INTRODUCTION

Alumina i s an a t t r a c t i v e m a t e r i a l f o r wear.and s t r u c t u r a l a p p l i c a t i o n because of t h e e x c e l l e n t p h y s i c a l p r o p e r t i e s such a s high melting p o i n t , e l a s t i c i t y , hardness and r e s i s t a n c e f o r chemical corrosion. Since f r a c t u r e toughness of alumina ceramic i s not enough high, however, t h e i f use under high s t r e s s f i e l d i s l i m i t e d . I t i s h i g h l y d e s i r a b l e t o improve t h e f r a c t u r e toughness o f alumina. I t i s well known t h a t uniform d i s p e r s i o n o f second-phase p a r t i c l e s i n t o b r i t t l e ceramic m a t e r i a l s may r e s u l t i n considerable improvement f o r t h e i r f r a c t u r e toughness; S i c and Tic p a r t i c l e s i n Si3N4 /1,2/, Tic and ZrO, p a r t i c l e s i n A1,03 /3-7/ and T i c , A1,03 and Z r O , A p a r t i c l e s i n SiC/8,9/. The i n c r e a s e i n f r a c t u r e toughness i s u s u a l l y

a t t r i b u t e d t o i n t e r a c t i o n of t h e crack f r o n t with t h e second phase p a r t i c l e s such a s pinning o r bowing o f t h e crack f r o n t by t h e second phase p a r t i c l e s /10/, microcrack formation i n t h e c r a c k - t i p r e g i o n /4/ and t h e s t r e s s - i n d u c e d phase t r a n s - formation /5-7/. Dispersion of ZrO, p a r t i c l e s i s one o f t h e most e f f e c t i v e method t o improve t h e f r a c t u r e toughn-ess of A1,03 ceramics /4-7/, b u t i t considerably reduced t h e hardness o f t h e composite ceramics. I t i s d e s i r e d t o i n c r e a s e t h e hardness of A1203-ZrO, compacts without l o s s o f t h e f r a c t u r e toughness. In t h e p r e s e n t study, S e r i e s o f experiments were c a r r i e d o u t , i n which v a r i o u s amount o f Z r O , c o n t a i n i n g 0, 3 and 6 mol% o f Y203 were dispersed i n A1,03 t o i n c r e a s e t h e f r a c t u r e toughness and nonoxide m a t e r i a l s such a s S i c , Tic, TiN and B4C were used t o improve t h e hardness o f A1203-ZrO, composites.

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EXPERIMENTAL PROCEDURES

A l 2 O 3 powders (AKP-20), c o p r e c i p i t a t e d f i n e g r a i n ZrO,(Y,O,) powders containing 0, 3 and 6 mol% Y203, denoted a s ZrO,OY, Zr023Y and Zr026Y, and S i c , Tic and BcC powders were used a s s t a r t i n g m a t e r i a l s . s e r i e s of composite powders of A1203, Zr02(Y203) and nonoxides were obtained by b a l l - m i l l i n g u s i n g t h e p l a s t i c c o n t a i n e r s and b a l l with acetone and drying. The composite powders obtained were u n i a x i a l l y pressed a t 300 MPa t o from p e l l e t s w i t h 5 mm i n diameter and 5 mm t h i c k , and t h e n

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19861111

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p e l l e t s were s i n t e r e d a t 1450 t o 1600O~ f o r 1 t o 50 h r i n a i r o r argon gas atmo- sphere, o r hot pressed a t 2.0 GPa and 1500°C f o r 30 min. Some o f t h e s i n t e r e d bodies were hot i s o s t a t i c a l l y pressed a t 1500°C and 200 MPa f o r 30 min. The bulk d e n s i t y o f t h e s i n t e r e d body was measured by t h e Archimedes technique. Micro- s t r u c t u r e o f t h e f r a c t u r e s u r f a c e was observed by scanning e l e c t r o n microscopy and average g r a i n s i z e o f specimen was determined by i n t e r c e p t method /11/. The phase i d e n t i f i c a t i o n was c a r r i e d out by X-ray powder d i f f r a c t i o n a n a l y s i s u s i n g N i - f i l t e r e d C u b . Scan o f 28 between 27 and 33 was conducted t o e s t i m a t e t h e mono- c l i n i c t o ( t e t r a g o n a l + cubic) z i r c o n i a r a t i o . Hardness, Hv, was measured by Vickers i n d e n t a t i o n w i t h loads o f 10 and 20 N. Young's modulus, E, was determined by Knoop i n d e n t a t i o n w i t h loads o f 20 and 50 N. F r a c t u r e toughness, KIC, was measured by using i n d e n t a t i o n technique /12/ a t loads o f 50 and 100 N.

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RESULTS AND DISCUSSION

(1) S i n t e r i n g of A1,03-Zr02(Y203) Composites

A1203-ZrO,(Y,O,) composites c o n t a i n i n g 0, 5 and 1 0 vol% o f ZrO,OY, Zr023Y and Zr026Y were s i n t e r e d a t 1450, 1500 and 1600°C f o r 1-50 h r . Since s i n t e r i n g behaviour hare n o t a f f e c t e d by t h e c o n c e n t r a t i o n o f Y203, s i n t e r i n g temperature dependences of r e l a t i v e d e n s i t y and g r a i n s i z e o f A1203-Zr020Y composites a r e shown i n Fig.1.Densification o f t h e s e composites were a l m o s t t h e same and r e l a t i v e d e n s i t y above 98 % of t h e o r e t i c a l d e n s i t y was a t t a i n e d w i t h i n 5 h r . However, t h e r a t e o f g r a i n growth s i g n i f i c a n t l y decreased with i n c r e a s i n g t h e amount o f ZrO,. A s seen i n Fig. 2, a t each temperature t h e r a t e o f g r a i n growth decreased with i n - c r e a s i n g t h e c o n c e n t r a t i o n o f ZrO, and reached t h e almost constant v a l u e a t 5 v o l % of ZrO,. These r e s u l t s agreed with t h o s e r e p o r t e d by Lange e t a 1 /13/. Vickers microhardness, Young's modulus, f r a c t u r e toughness and t h e concentration of

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100.

c

A 6-

o : ~ 1 2 0 3

A : AI 2 0 3 + 5 vol ^O/OZrOz OY

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^A: A I 2 0 3 + 10~01% Zr02 OY

P, L

a 88 I I I I I 1 o : ~ 1 2 0 3

A : AI 2 0 3 + 5 vol ^O/OZrO2 OY

Sintering time ( h r ) Concentration of Zr02 (v01 %)

Fig. 1

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S i n t e r i n g time dependence of Fig. 2 - Relationship between g r a i n s i z e r e l a t i v e d e n s i t y and g r a i n s i z e i n and concentration of Z r O , i n A1203-ZrO, Al,03-ZrO, composites s i n t e r e d a t composites.

1500°C.

t e t r a g o n a l ZrO, o f A120,-Zr0, composites s i n t e r e d a t 1 6 0 0 ~ ~ f o r 1 0 h r a r e shown i n Fig. 3. The c r y s t a l l i n e phases o f ZrO, i n A1,03-Zr023Y and A1,03-Zr0,6Y compos- i t e s were f u l l y t e t r a g o n a l and cubic, r e s p e c t i v e l y . On t h e o t h e r hand,

A1203-Zr0,OY ceramics were composed of t h e mixture o f t h e t e t r a g o n a l and monoclinic phases. The amount o f t e t r a g o n a l ZrO, decreased with i n c r e a s i n g t h e c o n c e n t r a t i o n

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c e n t r a t i o n o f Zr026Y, while KIC was almost constant. The decrease i n t h e v a l u e s o f H and E appeared t o be followed on a p r i n c i p l e o f a r u l e o f mixtures. In

A ~ , o , - z ~ o , ~ Y

system, t h e v a l u e s o f H and E changed i n t h e same manner a s t h o s e of A1,03-Zr0,6Y system, b u t t h e v a l u e s x f K appreciably increased with i n c r e a s i n g t h e concentration of Zr023Y. ~ h e r e f o r e , % h e in c r e a s e i n t h e v a l u e o f KIC might be due t o t h e s t r e s s - i n d u c e d phase transformation o f z i r c o n i a . On t h e o t h e r hand, i n Al,O,-ZrO, system, t h e KIC curve showed t h e maximum a t 1 0 v o l % o f Zr0,OY. The maximum value o f K was much g r e a t e r t h a n t h a t expected by s t r e s s - i n d u c e d phase transformation toukgening which was observed i n A1,03-Zr0,3Y system. The v a l u e s o f both H and E decreased w i t h i n c r e a s i n g t h e c o n c e n t r a t i o n o f ZrO,OY and were s i g n i f - i c a n t l y s m a l l e r t h a n t h o s e o f A1,03-Zr023Y and A1,03-Zr026Y composite ceramics.

Therefore, t h e i n c r e a s e of K i n A1,03-Zr0,OY composites i n t h e range o f l e s s than 1 0 v o l % ZrO, would be a t t r i b % e d t o t h e formation of microcrack i n t h e c r a c k - t i p region by t h e expansion of ZrO, d u r i n g t h e t e t r a g o n a l t o monoclinic phase t r a n s - formation. The decrease i n KIC a t above 10 v o l % ZrO, c o n c e n t r a t i o n might be due t o t h e j o i n i n g o f t h e microcracks between t h e p a r t i c l e s .

2 0

Fig. 3

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Young's modulus, V i c k e r l s

g

^{l 0} microhardness, f r a c t u r e toughness and

t h e c o n c e n t r a t i o n o f t e t r a g o n a l ZrO,

> U, i n Al,O,-ZrO, composites s i n t e r e d a t

0 1600°C f o r l 0 h r .

0 25 50 75 100 0' 25 50 75 10

(2) C h a r a c t e r i z a t i o n of A1203-Zr0,-Nonoxide Composites

A1,03-Za3,OY-nonoxide composites c o n t a i n i n g 1 0 v o l % o f TiN, T i c , SIC and B4C were hot pressed a t 1500°C and 2 GPa f o r 30 min. The v a l u e s o f r e l a t i v e d e n s i t y , H

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E and K C o f t h e composite ceramics a r e shown i n Table 1. Although t h e r e l a t i v e v d e n s i i l e s o f t h e composites were r e l a t i v e l y low, t h e v a l u e s o f Hv, E and K o f samples were g r e a t e r t h a n t h o s e o f Alto3-Zr0,OY composites. A s seen i n ~ a & E e 1, d i s p e r s i o n o f T i c and S i c were s i g n i f i c a n t l y e f f e c t i v e t o i n c r e a s e t h e v a l u e s o f Hv, E and K To examine t h e i n s i g h t o f t h e toughening mechanisms, crack p a t h s were observH5: Indentation crack p r o f i l e s of A1,03, A1,03-Zr0,OY and

A1,03-Zr0,OY-Sic ceramics a r e shown i n Fig. 4 (a)-(c'). The crack p a t h o f A1,0, remained f a i r l y p l a n a r through propagation. On t h e o t h e r hand, i n both s i n t e r e d A1,03-ZrO,OY and Al,03-Zr0,OY-Sic composites, t h e crack p a t h s e x h i b i t e d considerable d e f l e c t i o n . As seen i n Fig. 4 ( c ) , crack branching a l s o occurred i n

A1,03-Zr0,OY-Sic composite. These observation r e s u l t s confirmed t h e presence o f a s t r e s s - i n d u c e d microcrack zone. Therefore, t h e toughening i n A1203-Zr0,OY-nonoxide composites was due t o crack d e f l e c t i o n with microcracking.

The composites of A1,03-Zr0,OY-Sic, A1203-Zr0,OY-Tic, A1,0,-Zr023Y-Sic and A1,03-Zr0,3Y-Tic were s i n t e r e d a t 1500°C f o r 1 0 h r i n stream o f A r gas. Hot

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Table l

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Relative density, Vickers microhardness, Young's modulus and fracture toughness of A1203-Zr0,OY-nonoxide composites hot pressed at 1 5 0 0 ~ ~ and 2 GPa for 30 min.

Concentration of nonoxide: 10 ~ 0 1 %

Fig. 4

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Crack deflection profiles by Vickers indentation in A1,0,, A1,03-Zr0,OY and Al,O,-Zr0,OY-Sic ceramics.

isostatic pressing was also conducted to the sintered bodies of A1,0,-Zr023Y-Sic.

The values of relative density, H

,

E and K of those composites are shown in Figs. 5 and 6. As seen in these %igures, t6Ce relative density decreased with increasing the concentration of nonoxide materials. The values of Hv and E of A1,0,-Zr0,OY-Tic and A1,0,-Zr0,OY-Sic increased with the addition of 1 vol% of Tic

and Sic, and then slightly decreased with increasing both Sic and Tic concentra- tions. The decrease in the values of Hv and E would be due to the decrease in the relative density.We note that the relatlve density decreased to less than 93 % at 10 vol% of Sic and Tic. On the other hand, the values of H and K of

A1,0,-Zr0,3Y-Tic and A1,05-Zr0,3Y-Sic sintered bodies with %bout 9iC% of relative density were almost constant, while the values of K decreased a little. By hot isostatic pressing, the relative densities of

A ~ , o ~ ~ ~ ~ o , ~ Y - s ~ c

composites increased to more than 96.5 %, and values of H

,

E and KIC significantly increased. Namely, the values of H and E of

A~,o,-z~o,YY-s~c

fabricated by hot isostatic pressing for pre-sintered bo8ies were greater than those of fully dense Al2O3-Zr0,3Y composite, and those of K were almost same value of 7.5 M N / ~ ~ , . These results indicated that both toug6gning and hardening of A1203-ZrO, composites could be attained by dispersing nonoxide materials such as Sic and Tic into the Al,O,-ZrO, matrix.

E(GPa)

161 196 195 194 186 259 304 344 247 344 Composite

A120,-ZrO,OY-TiN Al,03-ZrO,OY-Tic A1,03-Zr0,OY-Sic A1,03-Zr0,OY-B4C A1,0,-ZrO,OY A1,0,-Zr020Y-TiN Al,O,-ZrO,OY-TiC A1,0,-Zr0,OY-Sic A1,0,-Zr0,OY-B$

Al,O,-ZrO,OY

(MN/~*)

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4.94 4.39

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4.58

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9.11 6.46 5.00 6.73 Volume ratio

of A1,0,/Zrn20Y

'I4

5 /4 5/4 5/4 5/4 8/1 8/1 8/1 8/1 811

Pth(%)

93.2 93.9 95.8 94.3 98.5 93.4 95.6 94.5 94.6 99.2

HV (GPa)

11.6 13.8 13.6 10.5 9.3 17.5 20.6 23.4 18.9 17.4

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Fig. 5

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R e l a t i v e d e n s i t y ,

1 5 Vickers microhardness, Young's

8

^{1 0} modulus and f r a c t u r e toughness

o f A1,03-Zr0,OY-Sic and A120,-Zr020Y-Tic composites s i n t e r e d a t 1 5 0 0 ' ~ f o r 1 0 h r .

' 0 2 4 6 8 1 0

Concentration of nonoxide added (v01

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^{9 6}

Fig. 6 - R e l a t i v e d e n s i t y , Vickers microhardness, Young's modulus and f r a c t u r e toughness o f A1203-Zr023Y-Sic and A1203-Zr023Y-Tic composites s i n t e r e d at 1500°C f o r 1 0 h r .

>

5

0 2 4 6 8 1 0

Concentrat~on of nonox~de added (v01 ^{% )}

REFERENCES

/ l / Lange, F. F., J. Am. Ceram. Soc. 56 (1973) 445.

/ 2 / Mah, T., Mendiratta, M. G. and L i p s i t t , H. A., Am. Ceram. Soc. Bull. 60 (1981)

1229.

/3/ Wahi, R. P. and I l s c h n e r , J. Mater. S c i , 1 5 (1980) 875.

/4/ Claussen, N., Steeb, J. and Pabst, R. F., Am. Ceram. Soc. Bull., 56 (19771 559.

/5/ Becher, P. F., J , Am. Ceram. Soc. 64 (1981) 37.

/6/ Becher, P. F., J. Am. Ceram. Soc. 66 (1983) 485.

/7/ Lange, F. F., J. Mater. Sci. 17 (1982) 247.

/8/ Faber, K. T. and Evans, A. G . , J. Am. Ceram. Soc. 66 (1983) C-94.

/9/ Wei, G. C. and Becher, P. F., J. Am. Ceram. Soc., 67 (1984) 571.

/10/ Lange, F. F., Philos. Mag. 22 (1970) 983.

/11/ Fullman, R. L., Trans. AIME 197 (1953) 447.

/12/ Niihara, K., Morena, R. and Hasselman, D. P. H., J.Mater, Sci. Letters, 1 (1982) 13.

/13/ Lange, F. F. and H i r l i n g e r , M. M., J. Am. Ceram. Soc. 67 (1984) 164.