3, By varying the structural parameters VVCo, dWC and ZSwc_Co in the mechanical model [9] it is possible to predict the mechanical properties of material which it will have when the specified microstructure is attained. I,[TERATURE CITED ]..

V. A. Ivensen, O. N~ Eiduk, and V. A, Chistyakova, "Dependence of the yield strength of the sintered alloy W C ~ o on the cobalt content and on the grai~ size of tungsten carbide," Proshk. Metall., No, 5, 84-87 (1974). 2. G. S. Kreimer, '1%ie Strength of Sintered Alloys [in Russian], Metallurgiya, Moscow (1971). 3. K. S. Chernyavskii and C. G. Travushkin, 'biodern notions on the connection between structure and strength of sintered alloys WC-Co," Probl. Prochn., No. 4, 11-]9 (1980)~ 4. J L. Cl~e~tmlant M. Coster, and F. Osterstock, [txllzatlon de la metallographie quantitative et de la sterologie a ].'etude des materiaux composites: application a ]_'etude de la rapture d'eprovettes de flaxion en WC-Co," Meta]].ography, No. 9, 504.-523 (1976). 5. J . L . Chermant and F. Osterstock, "Elastic and plastic characteristics of W C ~ o composite materials," Powder Met. Int., i]~, No. 3, 106-109 (1979)~ 6. J. Qurland, "The fracture strength of sintered WC-Co alloys in relation to composition and particle spacing," Trans. AIME, 227, No. i0, 1146-1150 (1963). 7. M. Hirao, R. Murata, and H. Takeyama, "Microscopic stress analysis of sintered carbides," Ann. CIRF, 26, No. i, 27-31 (1977). 8. M. Nakamura and J. Qurland, "The fracture toughness of W C ~ o two-phase alloys. A preliminary model," Met. Trans., IIA, No. i, 1,41-146 (1980). 9. M. G. Loshak and Yu. B. Gnuehii, "Mechanical model of the deformation ~nd fracture of sintered tungsten-cobalt alloys," Probl. Prochn., No. ]i, 42-54 (1983). i0. E. A. Shchetilina, "Investigation of the phase boundary of WC--Co alloys," Tsvetnye Met., No. 9, 85-89 (1971). ]].... M. G. Loshak, Strength and Endurance of Sintered Alloys [in Russian], Naukova Dumka, Kiev (1984).

STPdENGTH AND CIL~kCK RESISTANCE OF CE~M].CS BASED ON ZIRCONIUM DIOXIDE UDC 539.4:666.3:621.431

G. A. Gogotsi, Yu. I. Komolikov, D. Yu. Ostrovoi, S~ Yu. Pliner, D~ S. Rutman, and Yu. S. Toropov

Due to its high strength [i] and crack resistance [2] ceramic based on zirconium dioxide is currently being considered as a promising engineering material, q]-~ecomparatively high linear thermal expansion coefficient for this material [3] (close in value to that for metals) and low thermal conductivity makes it possible to hope for its successful application for preparing thermally stable components of combined adiabatic engines [4] whose use will improve the economics for means of transportation [5]. This cormnunication is devoted to studying creation i~ the Eastern Institute of Refactories of a prospective ceramic based on partially stabilized zirconium dioxide. Testing for this ceramic (Table i) was carried out by means of procedures described previously [6,

7]. A starting material for ceramic preparation was zirconium dio~cide powder with addition of 6% (by wt~) of yttrium oxide which was obtained by combined precipitation of the components from aqueous solutions. Sample blanks were formed by slip casting in a gypsum mold and annealed ~t 1400~ X-ray phase analysis showed that after annealing there was 90-95% of tetragonal and 510% of monoclinic zirconium dioxide in samples. Grain size was 0.5-I~5 ~m (Fig, I)~ After polishing with a diamond tool specimens were monitored with a microscope and those in which large defects were detected were scrapped. Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Eastern Institute of Refractories, Sverdlovsk. Translated,~from Problemy Prochnosti, No~ ]~ pp~ 50-52, January, 1988. Original article submitted April 8, 1986. 0039-2316/88/2001-0061512.50

9

1988 Plentu~ Publishing Corporation

61

T~LE i. Results of Testing on Z i r c o n i u m Dioxide ~echanical characteristics Density

[Z/S

5,81

velocity, 6058,0

D};'.~amic eia~;ticit} modulus, G ; F a biPa

Critical streas intep~sit) f a c t o r ~ MPa" m]d 2

Note. tained

0,095

1 63

6,490

0,10

__

'

Llti~at~ stre~'is

Based

SD

"]0 ;'~, kg/m 3

U V propas

Ceramic

__

214,0 0.,5(j . . . . . . 830,0 92,0 265,0 28,{1

0,24

9,30 3,38

8,90 ]!,0

0,83 0,]}]

I l,O 10,0

Data given b e l o w the line were obat 20~C, and above the line at 1000~

Fig. ].~ P h o t o g r a p h s of the fracture surfaces for ceramic based on z i r c o n i u m dioxide at 20~ (a) and IO00~ (b) o b t a i n e d by means of a C a m b r i d g e S t e r e o s c a n 84-10 m i c r o s c o p e = ~

)q~. Mpa,~,i~/2

b, HFa

i)~ i-< ........................................................................................................ ]I'Z (IX~

_j .........

20

1

.

~00

SgO

800

/,~["

Fig. 2. T e m p e r a t u r e d e p e n d e n c e s for ultimate s t r e n g t h (open points) and c r i t i c a l stress i n t e n s i t y factor (shaded points) for ceramic b a s e d on z i r c o n i u m dioxide (i) and r e a c t i o n b o n d e d silicon nitride NKI
62

~FP [a ~0 ?0[~................... [--

/4

200 IO0

-

0

~0

Fig. 3. Deformation diagrams for specimens at 20~ (X = I), straight line i, 500~C (X = i) straight line 2, 700~ (X = I) straight line 3, and 1000~ (X = 0.91), straight line 4. P ~FA

07--

< 0g97t........ }

08~[__ 200

4(!~ ~7<'

Oy.b, 2

4

$ fc MPa.m i/~

MPa

Fig. 4. Distribution of ultimate strength (o, A) and critical stress intensity factors (,, A) :for ceramic based on zirconium dioxide at 20~ (i) and 1000~ (2). thickness of the cross section (in this case 5 ram). Testing was carried out with three-point bending and a distance between the points of load application of 40 ~mu. Presented ceramic in the dependence for during testing

in Fig. 2 are the results of determining the ultimate strength of the test temperature range 20-1000~ Also shovm for comparison is the temperature the strength of reaction-sintered silicon nitride NKKKM [7]. ]it is noted that the ultimate strength of individual specimens reached 1 GPa.

In order to reveal features of the mechanical behavior of the ceramic, deformation diagrams were recorded for specimens 3.5 x 5.0 • 90.0 a m in size with fo~nr-point bending in the temperature range 20-I000~ (Fig. 3) in a TsD-4M unit. It can be seen from Fig. 3 that at 20-700~ ceramic based on zirconium dioxide is linearly elastic, but at IO00~ some inelasticity develops (the measure of brittleness is 0.91). In this case with determination of the ultimate strength consideration was given to deformation diagram nonlinearity. Fractographic studies did not reveal any marked changes in fracture surface morphology in the test temperature range in question. Statistical parameters for strength and crack resistance were studied at 20 and lO00~ Test results were treated by means of the procedure described previously in [6, 71. Presented in Fig. 4 on probability paper for Weibull distribution are experimental data which were approximated by a straight line, which confir~T~s the good conformity with the twoparameter Weibull model. Homogeneity coefficient m, determined by the least squares method, for ultimate strength distribution was 12.6 at 20~ and 1].2 at IO00~ and for critical stress intensity factor distributffon it was 12.7 and i0.0, respectively. 63

By comparing the data obtained with characteristics for a series of domestic and foreign cerami<" materials we see that at normal temperature the characteristics of the test ceramic are close to those for oxide materials, prepared by Japanese firms~ e.g,, U~]Z-IO [3] and TZ3Y [8]. It is noted that at IO00~ ceramic based on zirconium dioxide softens markedly and it does not have advantages compared with reaction-sintered silicon nitride NKKKH (Fig. 2). Thus, the ceramic studied may be used in different high-temperature units where high strength and crack resistance are required at comparatively low operating [.emperatures. The authors thank Ya. I. Grushevskii results

for help with statistical

LITERATURE

evaluation of the test

CITED

S. Yu. P l i n e r , Yu. S. T o r o p o v , D. S. Rutman, e t a l . , "Preparation of strong ceramic made o f z i r c o n i u m d i o x i d e by q u e n c h i n g and t e m p e r i n g ~ " Ogneupory~ No. 11~ 4 - 6 ( 1 9 8 4 ) . S. S k a ] n y ~ ~ C e r a m i c s i n the ] 9 9 0 s : Will they still be b r i t t l e ? " M a t e r . S o c . , 9~ No. 2~ 173-184 (1985) . NTK Z i r < o n i a C e r a m i c s ~ NGK S p a r k P l u g Co. L t d . ~ N a g o y a : H a m ~ f a < t u r e r T e c h n i c a l C e r a m i c s ~D i v i s i o n ( 1 9 8 2 ) . R. Kamo and W~ B r y z i c k ~ Cummlns/TACOM a d v a n c e d a d i a b a t i c enzir~e ~ SAE T e c h n . Pap S e t . , N840428, 2]-34 (i984). S. I~obb, "Cummins successfu]l~' tests adiabatic: engine," ~ r ~ Ceram~ So<:. 8 u l l ~ 62~ No. 7~ 755-756 (1983)~ G. A. Go~otsi~ V~ P~ Zavada~ a~d O. D. Shcherbina~ Strength and crack resistance of ceramic. Communication 2. Siiicor~ nitride ceramics" Probl. Proehn.~ No~ 12, 11-15 (1984)

7~

8.

64

.

(], A. Gogotsi~ V; P. Zavada~ a~d S. Ya, Kharitonov~ "Strength arld <.rack resistance of ceramics, Communication ]. Cordierite~" Probl. Prochn.~ No. 12~ 7-11 (1984)~ "Two world firsts from Toyo 8oda~" 7m~.. Ceram. Soc. Bull,~ 6~3~ No, 12~ 1483 (1984).