Deformation and fracture of CeO2-stabilized zirconia ceramics. I. Strength and deformability

Gogotsi, G. A.; Galenko, V. I.; Zavada, V. P.; Swain, Michael V.

doi:10.1007/bf02226979

Cited by 3 publications

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“…It should be noted that we have not observed (see, for example, [5]) a noticeable manifestation of a phase transformation in these crystals. Are these materials characterized by the effect of rotation of ferroelastic domains [21] or some other strengthening mechanism?…”

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confidence: 81%

“…It seems that the considerable value of these stresses leads, for example, to the formation of a large number of microcracks in crystals of the ZrO 2 -CeO2 system when the concentration of CeO2 in the charge is 5-9%. 4 In other words, it is impossible to obtain zirconia crystals that have the same concentration of CeO2 as is used for creating polycrystalline ceramics of the same composition (see, for exampie, [5]). …”

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confidence: 99%

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Zirconia crystals with yttrium and cerium oxides

et al. 1995

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Results obtained for a new material, namely, zirconia crystals stabilized by Y203 and CeO2 and containing a technological addition of neodymium oxide, tested at room temperature are described. Special features of the surfaces of the crystal blocks grown and the distribution of the additions introduced into the charge over their height are investigated. The dependences of the amounts of the stabilizing components and the fracture properties of the investigated material on its strength are determined. Certification results for the mechanical characteristics of the material are presented (mean four-point bending strength 1250 MPa, crack resistance in bending of a notched bar 11.43 MPa-m ~n at an elasticity modulus of 366 GPa for the crystallographic direction <100>). The crystals are investigated in the crystallographic plane { 100} by applying Vickers and Knoop indenters, and their hardness at different loads (beginning with 0.1 N) is determined. It is established that zones of phase transformations are formed near the indentations in addition to radial and lateral cracks. Problems of change in the specific features of the mechanical behavior of the crystals with change in the valence of cerium (most experiments were conducted for Ce203 ), with the heat treatment, etc. are considered. The results are analyzed using data of fractographic investigations and the new data obtained in tests of similar crystals partially stabilized by yt~ium and terbium oxides.It was established in the early 1980s [1] that crystals of partially stabilized zirconia possess relatively high mechanical parameters and other advantages that make them applicable for various purposes at temperatures up to 1600°C. However, these materials are not used in industry, although a technology for producing coarse crystals with high strength and crack resistance has been devised [2]. This can be explained by the fact that potential users have insufficient information on these crystals and that it is sometimes impossible to prepare materials with uniform structure and properties in an amount sufficient for practical purposes. In growing the crystals it is difficult to eliminate the appearance of cracklike defects, and in long-term storage they sometimes break spontaneously due to internal stresses. This shows that attention to investigating zirconia crystals for structural applications is insufficient. This especially concerns the interdependence of the technological regimes for preparing them, the phase composition, the structure, the laws governing their mechanical behavior, etc. On the whole, data that would make it possible to improve the production technology for these crystals and realize their potentialities are very scarce. As a continuation of previous work in this field [3], we present results of an investigation of crystals whose charge, in addition to zirconia (ZrO 2 ), contained Y203 and CeO 2 plus neodymium oxide 3 (Nd203 ) as a technological addition. These crystals were denoted Y-Ce-PSZ-K.Materials and methods. The experiments were conduct...

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Zirconia crystals with yttrium and cerium oxides

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“…The most intense phase transformations in our investigation were observed (see Table 4) in the 9Ce-TZP ceramics described in detail in our work [17]. In contrast to the TS, TSE, and TSN ceramics, in this material we could distinguish small radial cracks at the tip of the indentation (see Fig.…”

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confidence: 63%

“…The deformation diagrams (stress-strain dependences) of the 9Ce-TZP ceramics [17] have extended regions that distinguish them from TS, TSE, and TSN in which deformation grows virtually without stress growth. This is a good illustration of the considerable transformation pseudoplasticity [27] of this material and the extreme looseness of its structure in the zone of maximum stress concentration (Fig.…”

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Indentation resistance of zirconia ceramics and crystals

1996

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“…The measured results are highly divergent as a function of the method used for estimating the length of the cracks, namely, visual examination and determining the compliance of the specimens. It is assumed that the divergence can be attributable to the presence of a zone of transformation transitions at the tip of a crack and along it.In [1] we presented the results of testing ceria-stabilized zirconia ceramics for strength and deformability. The present work is devoted to the investigation of the crack resistance of such ceramics.…”

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Deformation and fracture of zirconia ceramics stabilized by CeO2. II. Crack resistance

et al. 1995

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Investigations of crack resistance of four types ofzirconia-base ceramics stabilized by 9% CeO2 are described. In three types of ceramics cracks develop against the background of the formation of a wide zone of transformation transitions, whose size decreases with decrease in the grain size of the materials. In the ceramics with the finest grain composition (1.14 lain) such a zone is absent. The measured results are highly divergent as a function of the method used for estimating the length of the cracks, namely, visual examination and determining the compliance of the specimens. It is assumed that the divergence can be attributable to the presence of a zone of transformation transitions at the tip of a crack and along it.In [1] we presented the results of testing ceria-stabilized zirconia ceramics for strength and deformability. The present work is devoted to the investigation of the crack resistance of such ceramics.We tested specimens 4.8 x 2.8 x 25 mm in size with an initial notch of depth 2.4 mm and width 0.25 mm for crack resistance. The specimens were subjected to three-point bending with the distance between the supports being 20 ram. In order to make observations of the initiation and development of cracks and the formation of a zone of transformation transitions easier, one of the side faces of the specimens was polished.We used the traditional technique of constructing Rcurves, although we were aware of its deficiency due to inelastic deformation of the ceramics. The technique was chosen because we were not convinced that the concept of J-integral was applicable to transformation-strengthened materials. The only energy parameter used was the specific energy of fracture.Just as in experiments on determining strength and deformability we recorded the dependence between the applied force P and the deflection 8 of a specimen (the P-5 diagram) and the acoustograms of force-total AE count (the P-N diagrams). The specimens fractured in a few loadingunloading cycles. After each cycle the length of the crack was where c o is the compliance of the specimen without a notch; Y is the K-calibration [3]; cz is the relative (with respect to the specimen's height h) depth of the stress concentrator.The P-5 diagrams for Ce-TZP-II ceramics are presented in Fig. 1, which also shows calculated (from the P -5 diagrams) dependences between the crack length lcr and the stress intensity coefficient K~, which is found from the relation of linear fracture mechanicswhere a is the nominal stress attained in the given load cycle. Despite the stepwise shape of the R-curves obtained, especially those for the visual data, we can say that the latter are quite different from the data determined from the compliance. Judging by the visual measurements, the values of K m tend to increase with the growth of a crack, while the results on compliance show a tendency to decrease. We can say that the Ce-TZP-II-Ce-TZP-IV materials virtually do not differ within the scattering range, whereas the Ce-TZP-I ceramics 0034-3102/95/3603-078512.50

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Deformation and fracture of CeO2-stabilized zirconia ceramics. I. Strength and deformability

Cited by 3 publications

References 5 publications

Zirconia crystals with yttrium and cerium oxides

Zirconia crystals with yttrium and cerium oxides

Indentation resistance of zirconia ceramics and crystals

Deformation and fracture of zirconia ceramics stabilized by CeO2. II. Crack resistance

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