CERAMIC MATERIALS IN THE SYSTEM MULLITE - ZrO2

(1)

HAL Id: jpa-00225506

https://hal.archives-ouvertes.fr/jpa-00225506

Submitted on 1 Jan 1986

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.

CERAMIC MATERIALS IN THE SYSTEM MULLITE - ZrO2

H. Hennicke, L. Frassek

To cite this version:

H. Hennicke, L. Frassek. CERAMIC MATERIALS IN THE SYSTEM MULLITE - ZrO2. Journal de

Physique Colloques, 1986, 47 (C1), pp.C1-729-C1-732. �10.1051/jphyscol:19861110�. �jpa-00225506�

(2)

Colloque Cl, supplkment au n02, Tome 47, fkvrier 1986 page cl-729

CERAMIC MATERIALS IN THE SYSTEM MULLITE

-

^{Z r O z}

H.W. HENNICKE and L. FRASSEK

Institut fiir Nichtmetallische Werkstoffe, Zehntnerstrasse Za, 0-3392 Clausthal-Zellerfeld, F.R.G.

Resume

-

Des produits ceramiques se composant de mullite et de zircone peu

-

vent etre fabriques par frittage reactif 2 partir de 1450°C. La zircone ainsi form6e est bien dispersee dans la matrice de mullite.

Les bonnes caracteristiques de ces produits ceramiques du point de vue de la resistance mecanique sont connues depuis plusieurs annees (renforcement par transformation)

.

L'influence d'une dispersion de particules de ZrOZ sur les caracteristiques physiques (risistance mkanique, r6sistance aux chocs thermiques, comportement de la d~latation thermique) sera expliqu6e.

Abstract

-

Ceramics, consisting of mullite and zirconia, can be made by reaction sintering from 1450 "C.

The developed ZrO2 is well-dispersed in the mullite matrix. The good behaviour of strength of such and similar ceramics are known since a lot of years (transformation toughening 1.

The influence of the dispersed zirconia-particles on strength, thermal expansion coefficient and thermal shock resistance of the produced ceramics is discussed.

I

-

INTRODUCTION

The aim of this study was to produce a ceramic in the system mullite

-

Zr02 and to investigate its thermal shock resistance. Ceramics of this system can be made by sintering mullite and Z r q or /l 1 / by reaction sintering after equation ( 1 ) /l /. In this study reaction sintering was prefered since mullite could not be sintered to a satisfying density/l3/.

(1 ) 2 Z r 9 *Siq + ^{3 A12}4 ⁺^3A12

4

*2Siq + 2Zr02

The reaction given above was investigated in detail by Rupo, Wallace and others /1,2,3,8112/-

The ceramics produced by reaction sintering have two main preferences:

1st a very low thermal expansion because of the high mullite content (50 weight%) and

2nd a higher strength due to transformation toughening, which is caused by finely dispersed tetragonal stabilized Z r 4 particles.

The fact of transformation toughening in ceramics is well known for some time now /4,6/. Stabilization of tetragonal Z r Q in a mullite matrix was examined in detail by Wallace /12/ and Claussen /3/, who found evidence that the content of the tetragonal phase has a great influence to the strength in such ceramics. According to Hasselman /l0 / and Nakayama /9/ the improvement of these two properties, thermal expansion and strength, should have a positive effect to the thermal shock resistance to these ceramics.

Further attempts in order to improve the thermal shock resistance were made by producing microcracks into the microstructure by inserting additional monoclinic ZrO2 and to lower the thermal expansion by using several grain fractions.

Theoretical conceptions were discussed by Claussen /6,7/.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19861110

(3)

JOURNAL DE PHYSIQUE

I1

-

EXPERIMENTAL METHODS

M u l l i t e

-

^{Z r O} ceramics were produced by r e a c t i o n s i n t e r i n g a t 1550 OC a f t e r e q u a t i o n (1 )

.

²

The s t a r t i n g powders ~ l 2 0 ~ * , z i r c o n + , and 2ro2# were mixed f o r 12 h i n a p o r c e l a i n m i l l with A1203 b a l l s i n i s o p m p a n o l without having a remarkable g r i n d i n g e f f e c t . Mixture r a t i o s ( m o l a r ) of 1 . l , 1.5, 2.0 A1203/zircon ( i n one case with -0,-additions) were examined. The d r i e d suspension was crushed and g r a n u l a t e d by s i e v i n g and subsequently i s o s t a t i c l y p r e s s e d a t 170 MQa. These samples were s i n t e r e d f o r 6 h a t 1550 OC ( h e a t i n g r a t e 20 'K/min), some of them had been p r e s i n t e r e d f o r 1 h a t 1400 "C, which was below r e a c t i o n temperature.

Fig. 1 shows t h e time

-

temperature curves of used h e a t i n g programs.

A f t e r s i n t e r i n g t h e thermal expansion c o e f f i c i e n t , MOR (RT), r e a c t i o n p r o g r e s s and thermal shock r e s i s t a n c e a f t e r Hasselman were determined. The MOR was o b t a i n e d a t b a r s of 3*5*33 mm3 by t h e t h r e e p o i n t bending method with a crosshead speed of 0.1 mm/min. The r e a c t i o n p r o g r e s s could be determined by XRD and t h e thermal expansion c o e f f i c i e n t by a l a s e r d i l a t o m e t e r . Thermal shock r e s i s t a n c e a f t e r Hasselman was i n v e s t i g a t e d by measuring MOR (RT) of samples quenched i n water. The m i c r o s t r u c t u r e was determined by SEM on thermal etched ( 1 400 'C, 60 min and p o l i s h e d samples.

I11

-

RESULTS AND DISCUSSION

The r e a c t i o n a f t e r 6 h s i n t e r i n g was complete f o r t h e mixture r a t i o s A/Z 2.0 and 1 .l

.

Using t h e s t o i c h i o m e t r i c r a t i o A/Z 1.5 t h e r e a c t i o n p r o g r e s s was n o t complete, even a f t e r g i v i n g t h e m a l o n g e r s i n t e r i n g time, i n s t e a d an e q u i l i b r i u m was e s t a b l i s h e d . The d e n s i t y of t h e ceramics was between 88

-

⁹²^% ^of t h e t h e o r e t i c a l d e n s i t y . Approximately 30 W/% of t h e ZrO2 i n t h e samples turned o u t to be t e t r a g o n a l s t a b i l i z e d , which was determined by a formular a f t e r Garvie and Nicholson /5/.

The p r e s i n t e r e d samples (PS

-

program) showed two M s ( m a r t e n s i t e s t a r t )

-

temperatures a t 800 "C and 600 'C, Fig 2. Fig. 3 explained t h i s behaviour. The -02 and z i r c o n showed a g r a i n s i z e d i s t r i b u t i o n devided i n t o two main p a r t s . I t seemed t h a t t h e PS

-

samples were a b l e to keep up t h i s g r a i n s i z e s e p a r a t i o n , t h i s way a mechanical f a s t e n i n g of t h e z i r c o n p a r t i c l e s could have r e s u l t e d d u r i n g t h e p r e s i n t e r i n g . Due to t h e s e two MS

-

temperatures t h e thermal expansion c o e f f i c i e n t of t h e PS

-

samples was lowered i n t h e range between 500 "C

-

1000 "C, which had a p o s i t i v e e f f e c t to t h e thermal shock r e s i s t a n c e .

The f l e x u r a l s t r e n g t h s were i n t h e range between 200

-

^{350 MPa.}

A s t h e c o n t e n t of t e t r a g o n a l s t a b i l i z e d -02 was r e l a t i v e l y small, t h e t r a n s f o r m a t i o n toughening e f f e c t could n o t be examined. Nevertheless abrading t h e s u r f a c e r e s u l t e d i n transforming t h e t e t r a g o n a l Zr02 p a r t i c l e s , which had a s t r e n g t h improvement i n consequence.

Fig. l : Diagram of the t i m e

-

t e m p e r a t u r e

s i n t e r i n g c u r v e s ( s e e t e x t ) d o t t e d l i n e =

p r e s i n t e r i n g program PS

t i m e

* Alcoa A1 6-SG 99% C 2.4pm

+ U l t r o x 1000 W and s t a n d a r d by Reimbold & S t r i c k (GER)

# Dynazirkon MS, Dynamit Nobel ( G E R ) 80% < 1 Opm (monoclinic)

(4)

1. I n c r e a s i n g t h e s t r e n g t h i n o r d e r to suppress t h e f r a c t u r e i n i t i a t i o n 2. I n c r e a s e t h e toughness, which h i n d e r s t h e c r a c k propagation

Fig. 4 shows t h e r e t a i n e d MOR of produced ceramics without a d d i t i o n a l WO2 a s a f u n c t i o n of t h e i r quenching temperature d i f f e r e n c e . R e l a t i v e l y small temperature shocks caused a remarkable s t r e n g t h d e c r e a s e , which was a t y p i c a l c h a r a c t e r i s t i c of high s t r e n g t h fine-ceramics ( p.e. A 1 O3 /9/ ).

The 2nd concept, i n c r e a s i n g t h e &ughness, appeared to be a c h i e v e a b l e by Zr02 a d d i t i o n s . I n v e s t i g a t i o n s showed a f u r t h e r d e c r e a s e of t h e thermal expansion c o e f f i c i e n t , Tab. 1 and Fig. 2, and a m i c r o s t r u c t u r e with more microcracks t h a n i n conventional ceramics, which explained t h e h i g h e r r e t a i n e d s t r e n g t h , Fig. 4.

Nakayama determined t h e r e t a i n e d s t r e n g t h f o r c e r t a i n i n i t i a l crack l e n g t h s t o be

-

^l

^/G,

which meant, t h e high r e t a i n e d s t r e n g t h could be caused by low i n i t i a l s t r e n g t h s a s well.

Fig. 2: Dilatation

-

temperature curves ( E = A l/lo )

.

⁼^A/Z= ²

I = range of error

I

200 4 0 0 600 8 0 0 1000 1200

quenching temperature difference/K

Fig. 3: Grain size distribution of used zircon Q3= voll of particles r

8 4 rSq= 8qui. radius from laser

beam methcd

Fig. 4: Retained MOR after the Hasselman-test

(5)

JOURNAL DE PHYSIQUE

Tab. 1 : Thermal expansion coefficients of mullite-zirconia ceramics

IV

-

^SUMMARY

thermal expansion coefficient -10 6 (cooling 900-500°C) / 1 /K

3.750.2 4.3 3.9 4.9 4.9 5.1 2.9

The thermal shock resistance of the examined -02

-

mullite ceramics showed the same characteristics as other dense fine ceramic materials meaning great strength decrease after relatively small temperature shocks.

Additional Zr02 and a wide grain size distribution of the present Zr02 effected a strong decrease of the thermal expansion (cooling) having a positive influence to the thermal shock resistance.

Furthermore there was no remarkable effect of transformation toughening to the thermal shock resistance. Presintering at ca. 1400 'C before the actual reaction sintering stabilized the initial grain size distribution of Zr02.

heating program PS

normal PS normal

PS normal

PS No.

1 2 3 4 5 6

-

7

REFERENCES

A/Z (molar) 2.0 2.0 1.5 1.5 1 .l 1 .l

2.0+1 Ow/% Zr02

/l/. Rupo, E. di; Anseau, M.R. J-mat-sci. E ( 1 9 8 0 ) p. 114-118

121 Wallace, J.S. ; e.a. Materials Science Research Vo1.9, Plenum Press NY 193 1 /3/. Claussen, N. ; Jahn, J. J.Amer.Ceram.Soc. 6 3 (1980 ) p. 228 -229

141 Porter, D.L. ; e.a. Acta metallurgica 27 (1979 ) p. 1649-1654

151 Garvie, R.C. ; Nicholson, P.S. J.Amer.Ceram.Soc.

55

(1972 p. 303-305 161 Claussen,N. Z. Werkstofftechn. 13_ (1532) p. 138 -147 & p. 185-195 171 Claussen, N. Ber.Dt.Keram.Ges. 5 4 (1977 ) p. 420-423

181 Prochazka; e.a. J.Amer.Ceram.Soc. & (1983) C 125-C 127

191 Nakayama,K. EYacture Mechanics of Ceramics 2, Plenum Press NY 1974 1101 Hasselman, D.P.H. J.Amer.Ceram.Soc. 5 2 (1969) p. 600-604

1 1 1 1 De Portu, G.; Henney, J.W. Br.Ceram.Trans.J. 8 3 (1984) p. 69-72 1121 Wallace, J.S. Ph.D. Thesis, Univ. Stuttgart (GER) 1533

1131 Mazdyasni, K.S.; Brown, L.M. J.Amer.Ceram.Soc. (1972 p. 548 .552