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MICROSTRUCTURE AND MECHANICALBEHAVIOUR OF Al2O3 - ZrO2 (Y2O3) ORIENTED

EUTECTICSL. Mazerolles, D. Michel, R. Portier

To cite this version:L. Mazerolles, D. Michel, R. Portier. MICROSTRUCTURE AND MECHANICAL BEHAVIOUR OFAl2O3 - ZrO2 (Y2O3) ORIENTED EUTECTICS. Journal de Physique Colloques, 1986, 47 (C1),pp.C1-335-C1-339. �10.1051/jphyscol:1986149�. �jpa-00225579�

https://hal.archives-ouvertes.fr/jpa-00225579https://hal.archives-ouvertes.fr

JOURNAL DE PHYSIQUE Colloque C1, suppl6ment au n02, Tome 47, fbvrier 1986 page c1-335

MICROSTRUCTURE AND MECHANICAL BEHAVIOUR OF A1, O3 - ZrO, (Y, 0, ) ORIENTED NTECTICS

L. MAZEROLLES, D. MICHEL and R. PORTIER

C . N . R . S . UA 302, C.E.C.M., 15 R u e G. Urbain, F-94400 Vitry, France

Resum6 - Des eutectiques orientes A1203-Zr02 (y203) prepares par solidifica- tion unidirectionnelle ont 6te etudies. Leur microstructure, l e s interfaces

entre l e s dispersoi'des de zircone e t l a matrice d'alumine ainsi que l e s sur- faces de fracture ont et6 observees en microscopie electronique en transmis- sion e t en balayage.

Abstract - Oriented A1203-Zr02 (Y203) eutectics prepared by directional so l i - di f ication were studied. Microstructure features, interfaces between zi rconia

dispersoyds and the alumina matrix as well as fracture surfaces were observed by transmission and scanning electron microscopy.

INTRODUCTION Alumina ceramics containing a f ine dispersion of cubic or tetragonal zirconia

par t ic les are known to exh-ibit enhanced mechanical properties and especially a high fracture toughness (1-5).

In order to interpret the influence of dispersoi'ds on the fracture behaviour, samples with controlled microstructure and crystallographic orientations were prepa- red a t two eutectic compositions by directional solidification from the me1 t. Detai 1 s concerning the preparative conditions and microstructural features are reported in previous papers (6-7).

The present paper deals with transmission and scanning electron microscopy observations of interfaces and fracture surfaces. MICROSTRUCTURE AND INTERFACES

The composition and data concerning the studied eutectics are gathered in the following table.

Table 1 - Cornposition and constituent phases of the studied A1203 - Zr02 (Y203) eutectics.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986149

http://www.edpsciences.orghttp://dx.doi.org/10.1051/jphyscol:1986149

C1-336 JOURNAL DE PHYSIQUE

With the growth rates used in th i s study ( s 1-2 cm/hour), a dendritic cellu- l a r growth occurs and zirconia part icles with s ize about 0.5 Dm and interspacing about 1 pm are dispersed in an alumina matrix.

The TEM image shown on Figure I i s typical of such a microstructure. The sample i s a transverse section of an eutectic rod thinned by argon ionic bombar- dment. This treatment induces a preferential wear of Zr02 part icles which can be observed on the specimen edge.

Preferred directions for the simultaneous crystal growth of alumina and zirconia have been determined as well as principal epitaxy relat ions between Zr02 and A1 03. Preferred growth directions are and f o r the alumina matrix and or for zirconia dispersoYds. More detailed resul ts concerning inter- faces and crystal lographic relat ions are exposed el sewhere ( L . Mazer01 l e s , D. Michel R. Portier, t o be pub1 ished).

Interfaces are generally faceted and coherency between A1 0 and ZrO atomic rows has been observed fo r planar boundaries as shown on Figure $ . 3 ~ h i s hig(

resolution image corresponds to a 12FiO}A1 1100}zro2

observed in projection on 2 3

a section COIiO}A1 // {010)zro2. Inset represents the corresponding projection of 2 3

l a t t i c e nodes and arrows indicate-the regular corncidence of A1203 and Zr02 atomic rows.

Fig. 1 - Transmission electron micrograph of a A1203 - Zr02 (Y203) eutectic. Transverse section {OliOIAl // {OIO)Zr02.

2 3

Fig. 2 - High r e s o l u t i o n image o f a { 2 i i 0 l A 1 // i100}Zr02interface 2 3

Transverse sect ion {O1iO}A, // 1010)zr02. 2 3

Epitaxy r e l a t i o n s : (0001)A1203 // (oo1)zro2

C1-338 JOURNAL DE PHYSlQUE

MECHANICAL BEHAVIOUR

H a r d n e s s a n d f r a c t u r e t o u g h n e s s w e r e m e a s u r e d b y V i c k e r s inden ta t ion on transverse sect ions o f e u t e c t i c rods. Notched-beam experiments i n three-point bending confirmed the KIC values ( t h e length o f specimen was a1 igned w i t h the growth d i r e c t i o n ) .

The values of hardness H, toughness K and Young's modulus E a t room tempe- r a t u r e are the f o l lowing for the < 0 0 l > ~ ~ 203 / ~ C < O ~ l > z , O Z o r i e n t a t i o n o f a A1203-ZrOZ (3 mol % Y203) e u t e c t i c :

H = 18 GPa KIC = 6.8 ~ ~ a . r n I / z E = 335 GPa

Toughness values were est imated from Vickers inden ta t ion and confirmed by notched-beam experiments.

F igure 3 shows the general aspect o f the f r a c t u r e surface o f a A1203-Zr02 (Y203) eu tec t i c . Fracture propagates by cleavage i n the alumina matr ix . A t h igher magnif icat ion, the roughness o f the surface can be observed, espec ia l l y around the l o c a t i o n o f ex t rac ted z i rcon ia p a r t i c l e s . These observat ions could exp la in the enhanced toughness o f t h i s mate r ia l w i t h regard t o t h a t o f alumina.

Fig. 3 - Fracture surface o f a A1203-Zr02 (3 mol % Y203) e u t e c t i c .

ACKNOWLEDGMENTS

The authors are indebted t o Drs C. Gaul t and B. Ro eaux (ENSCI Limoges) f o r measurements o f mechanical p roper t ies and t o J.C. Mar t in ~cNRS Bel levue) f o r SEM observat ions.

REFERENCES

/ I / Hulse, C. and Bat t , J.A., Final Rept. UARL N-910803 (1974) 10. /2/ Claussen, N . , J. Am. Ceram. Soc. 2 1-2 (1976) 49. /3/ Science and Technology of Zirconia. Ed. A.H. Heuer and L.W. Hobbs -

Advances in Ceramics Vo1.3. The American Ceramic Society (1981 ) . /4/ Science and Technology of Zirconia 11. Ed. A.H. Heuer, N. Claussen and 1.1. Riihle.

Advances in Ceramics Vo1 .12. The American Ceramic Society (1984).

/5/ Lange, F.F., J . Mater. S c i . , 17 1 (1982) 247. /6/ Mazerolles, L., Michel, D . , Perez y Jorba, M., Stud. Inorg. Chem. 3 ,

Ed. P. Metselaar, Hei j l igers and Schoonmans - El sev ie r S c i e n t i f i c Pub1 i sher (1984) 841.

/7/ Michel , D., Mazerolles, L. , Dal las , J.P., Stucky, M. , P o r t i e r , R., Phys. Chem. Sol. S ta te . Ed. P. Lacombe - Elsevier Science Pub1 i sher (1984) 397.