V. I. Galenko

Fracture toughness, strength, and other characteristics of yttria-stabilized zirconium ceramics

The mechanical behavior of zirconium ceramics with different porosities (456 and 1330 MPa) is studied with an accent on the fracture toughness (the study of other characteristics in a wide temperature range plays an auxiliary role) The tests are predominantly performed with the use of a Vickers pyramid (theIF andIS methods) and under flexure (theSEVNB andSENB methods) The results of the indentation and subsequent bending of the specimens are used to plot aR-curve that turns out to be plane It is shown that despite the substantial difference in the strength of the studied variants of ceramics their crack resistance differs inconsiderably The values of the critical coefficients of stress intensity determined by various methods for the same ceramics are shown to differ The results obtained are analyzed using the data of a micro-Raman analysis The tests for crack resistance by the method ofSEVNB (bending of a beam with a polishedV-notch) show that the specimens do not undergo a tetragonal-monoclinic phase transformation during the deposition of a stress concentrator

The Mechanical Behavior of Lanthanum Cobaltite-Based Perovskites with a Mixed Ion-Electron Conductivity at Different Temperatures

The mechanical behavior of a perovskite-type ceramic based on partially substituted lanthanum cobaltites is studied over a wide temperature range. The La0.8Ca0.2CoO3 composite is shown to be the most inelastically deformable, high-strength, and crack-resistant. In perovskites, the brittleness can be considered as a measure of both inelasticity and ferroelasticity. The perovskites are tested for deformability using bending and indentation techniques, and an analogy in the results obtained by the two techniques is noted. Specific features of the fracture of perovskites tested by the Vickers indentation method are discussed. The crack resistance and stress-strain diagrams of the La0.8Ca0.2CoO3 composite are studied as a function of temperature. Fractographic test data are used to analyze the results obtained.

PROBLEM OF EVALUATING THE CRACK RESISTANCE IN CERAMICS OF Si3N4 AND ZrO2

The mechanical behavior of silicon nitride and zirconium dioxide ceramics is investigated in a wide temperature range. Much attention is paid to crack resistance under the conditions of the ambient. Data obtained by different methods used for evaluating crack resistance are analyzed, and it is shown that the best results have been obtained in tests in which the concentrator was an indentation of a Vickers pyramid. The analysis was conducted using fractographic investigations of the materials and data of tests of a model material of zirconium dioxide.

Edge Fracture Resistance of Glasses: Different Conical Indenters and the Fracture Initiation Barrier

An increased fracture initiation barrier of brittle materials is examined by the example of test results for flat glass. The fracture resistance of this glass on the rectangular specimen edge chipping with conical diamond indenters of different tip radii (11–800 μm) was evaluated. Optical glasses (quartz and light crown) were used for comparison. A significant change in glass behavior on the edge chipping of their specimens is observed only with the indenter of an 11-μm tip radius. In this case, the crack resistance of glasses is equal to that measured in Vickers experiments. Any basic differences in the fracture behavior of glasses with the indenters of tip radii of 100 and more micrometers were not revealed. The prescratching of the glass specimen surface near its edge before its chipping was noticed to exert negative effect on crack resistance estimates since its characteristic fracture initiation barrier is damaged.

Crack resistance and other characteristics of ceramics of partially stabilized zirconia with an iron oxide additive

The strength, toughness, hardness, and crack resistance of ceramics based on zirconia stabilized by yttrium oxide and having iron oxide as a reinforcing component are investigated. Certain features of this material are studied in detail at low and high temperatures. It is established that the ultimate strength in three-point bending is 977 MPa, and the critical coefficient of stress intensityKIc for a notched beam can attain 16.7 MPa · m1/2. Different testing methods are used and analyzed in the investigation of crack resistance. For example, it is shown that in bending a beam indented under a load of 500 N the value ofKIc at room temperature is 9.5 MPa · m1/2 and after cooling to − 140°CKIc is 12.3 MPa · m1/2. For this testing method the dependence ofKIc on the length of a radial crackcav is established. The results are analyzed with the use of additional data and a fractographic investigation.

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

Investigations of the strength and deformability of four types of zirconia-base ceramics stabilized by 9% CeO2 (9Ce — TZP) and having different grain sizes (from 1.4 to 3.0 µm) are described. Under mechanical loads these materials exhibit “avalanche” formation of wide transformation zones. A correlation is established between the special features of the formation of such zones, the deformability of specimens, the the acoustic emission in them, and the grain composition of the material.

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

Investigations of crack resistance of four types of zirconia-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 µm) 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.

Evaluation of the heat resistance of new cordierite-base materials

ConclusionsThe results of the comparative evaluation of the heat resistance of the chamotte-cordierite and corundum-cordierite materials developed make it possible to conclude that they possess significant resistance to thermal failure and may be used in structures with sharp temperature differentials. The structure of the material and also the phase transformations in the high-alumina area of the MgO-Al2O3-SiO2 system have the primary influence on the character of failure and the resistance to the action of a failure crack.