HIGH RESOLUTION ELECTRON MICROSCOPY OF MONOCLINIC ZrO2

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HIGH RESOLUTION ELECTRON MICROSCOPY OF MONOCLINIC ZrO2

G. van Tendeloo, L. Anders, G. Thomas

To cite this version:

G. van Tendeloo, L. Anders, G. Thomas. HIGH RESOLUTION ELECTRON MICROSCOPY OF MONOCLINIC ZrO2. Journal de Physique Colloques, 1982, 43 (C4), pp.C4-411-C4-412.

�10.1051/jphyscol:1982461�. �jpa-00222179�

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JOURNAL DE PHYSIQW

CoZZoque C4, suppl6ment au n o

12,

Tome

43,

de'cembre

1982

page

c4-411

HIGH RESOLUTION ELECTRON

MICROSCOPY

OF MONOCLINIC Z r 0 2 G. Van ~ e n d e l o o *

,

L. Anders and G. Thomas

Department of Materials Science and Mineral Engineering

and

the Lawrence Berkeley

Laboratory,

University of California, Berkeley,

CA 94720,

U. S.A.

(Accepted 9 August 1982)

I n the course o f a more general study o f the ZrO - Z r N system, ZrO was sintered i n N a t

2 2

1 9 0 0 y for one hour and Z r 0 2 - Z r N compounds cont&ning 2.5, 5, 15, o r 75 mol% Z r N were prepared under the same conditions. This paper w i l l t r y t o shed some new l i g h t on the martensite transformation i n ZrO and elucidate the resulting domain structure by means o f high resolution electron microscopy combined w i t h optical d i f f r a c t i o n and/or convergent beam 2 micro-electron diffraction.

As a function o f decreasing temperature ZrO undergoes the following phase transitions

<- ²

cubic <=> tetragonal -> rnonoclinic (see e.g. [ l ] )

where the last transition around 1 0 0 0 T has been proved t o be martensitic [2],[3],[4]. This phase transformation has been the subject of a number o f controversies (see e.g. [ 4 ] ) concerning the l a t t i c e correspondence between product and parent phase and concerning the exact habit plane.

A bright f i e l d image o f Zr02-2.5% Z r N is reproduced I n Fig. la. It reveals different variants o f the rnonoclinic phase, a l l having their c-axis parallel t o the electron beam. The resulting diffraction pattern i n the correct orientation is shown as an inset; originally cubic reflections are jndicated. It i s clear that a l l habit planes are s t r i c t l y (lOO)mo

,

(O1O)mon, (110), and (llO)mon. Optical d i f f r a c t i o n and convergent beam electron d i f f r a c f i o n o f these twinne8 areas, belng

-

20nm wide, c o n f i r m the orientation relationship between variants proposed i n Fig. l b . The indicated a-axis is in f a c t the projected one along the c-axis. I n reciprocal space it makes an angle o f 99O w i t h this c-axis. The spot splitting observed i n the diffraction pattern is the result o f twinning on (110) planes only; (100) or (010) twinning does n o t produce any d i f f r a c t i o n e f f e c t i n the [ O O l ] projection.

The boundary region between the rnonoclinic phase and the retained cubic phase (upper p a r t i n Fig. l a ) i s not sharp, one seems t o dissolve slowly i n the other; moreover, the retained cubic m a t r i x contains small "microdomains" exhibiting the same contrast as the monoclinic transformed regions. They might be rnartensite nuclei generated under the electron beam or during the ion milling preparation o f the specimens, their further growth being l i m i t e d by the f o i l thickness.

More structural details o f this transformation obtained using high resolution electron microscopy and structural considerations concerning the possible orientations are t o be published elsewhere.

The authors would l i k e t o thank Dr. J. Weiss f o r providing the Z r 0 2 - Z r N material and Dr.

U. Dahmen and L. Tanner f o r not only stimulating b u t useful discussions. This work was suppor- ted i n p a r t by the D O E Contract No. DE-AC03-76SF00098 and by the National Science Foundation.

[l] SUBBARAO, E. C. i n Advances i n Ceramics 111, eds. A. H. Heuer and L. W. Hobbs, Amer. Ceram. Soc. (1981).

121 WOLTON, G. M., J. Am. Ceram. Soc. 46,418 (1963).

[ 3 ] BAILEY, J. E., Proc. Roy. Soc. London 279 395 (1964).

141 BANSAL, G. K. and HEUER, A. H., ~ c t a ' e t .

XI,

1281 (1972);

zz,

409 (1974).

"on l e a v e from RUCA, U n i v e r s i t y o f Antwerp, Groenenborgerlaan 171, B-2020 Belgium

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982461

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C4-412 JOURNAL DE PHYSIQUE

Fig. 1. a. Lower magnification of a monoclinic Z r 0 2 area. The monoclinic c-axis is perpen- dicular t o t h e foil.

b. High resolution image of t h e a r e a indicated in

a;

t h e relationship between orientation variants has been indicated.

c. Boundary region between t h e monoclinic a r e a (rnon) and t h e cubic matrix (cub).

Note t h e microdomains in t h e cubic area.