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The recent technological developments [1] make it possible to treat the crystals of zirconium dioxide partially stabilized with yttrium oxide (Y-PSZC) as modern structural materials that can fred several applications in technology and medicine. These crystals can be obtained using the same raw materials as those used for obtaining partially stabilized and tetragonal polycrystalline ceramics (but without stringent specifications with respect to the morphology and the particle size of the original powder). They are used effectively up to a temperature of 1500-1600~ [2] owing to their continuous structure (without grain boundaries and the undesirable consequences due to their presence) and the other features distinguishing them from the conventional materials.However, Y-PSZC has not been studied extensively (in particular, in our countries). The investigations carried out on this material aim mainly at understanding the behavior of the crystals containing only yttrium oxide as a stabilizing additive.The situation regarding the research on the effect of the additives is far from being satisfactory. It is known that the addition of a small quantity (0.01-0.5%*) of the rare-earth oxides (for example, Tb203) in a specific range of concentration of the stabilizing oxide does not change the phase composition of the crystals but can change their properties [3, 4]. In view of this, we continued our studies on the effect of the additives on the mechanical behavior of the aforementioned crystals [5, 6] and investigated the behavior of the crystals of Y-PSZC containing terbium oxide that were synthesized for the ftrst time under experimental-industrial conditions. Materials and Experimental Procedure. Studies were carried out using the crystals grown in a cold container (CC) according to the method described elsewhere [11. In order to prepare charges for obtaining single crystals, we used the "purity" grade zirconium dioxide powder (containing ZrO 2 > 99%), the ItO-Lyum grade (purity 99.99%) Y203 powder, and the TbO-3 grade (purity 99.9%) TbzO 3 powder.When selecting specimens, we took into account the nature of the temperature variation along the diameter of CC that owes to the specific features of heat liberation in the melt located in a high-frequency field [7] and leads to different conditions of crystal growth at the center of this container and in the vicinity of its cooled walls. As a result of this, columnar crystals having the same cross sectional area at the beginning and the end of their growth form in the central zone (zone 1) extending over approximately 0.25D c (D e is the diameter of CC). In zone 2 (measuring 0.1-0.15D c) adjoining the walls of CC, crystals having 2-3 times larger transverse dimensions towards the end of their growth than at the beginning of growth and elongated in the direction of the walls are developed. In the intermediate zone (zone 3), the cross section of these crystalline blocks is either uniform or nonuniform. Besides this, during the emergence of the crystals from the zone of growth,...

Ключевые слова: керамика, скалывание кромки, краевая вязкость разру шения, индентирование.Introduction. Ceramics are widely used in industry, medicine, and everyday life. Being brittle materials, they can undergo catastrophic failure in operation, e.g., even first efforts to manufacture ceramic gas-turbine blades have revealed this critical tendency [1]. An increased sensitivity to stress concentrations and low resistance of the edges to flaking, which can account for uncontrolled failure, also cause certain concern.With an improvement in the characteristics of ceramics and a continuous growth in production volumes of ceramic items, fracture resistance of these materials attracts the particular attention

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Fracture resistance of technical quartz and normal window glasses was investigated in testing polished rectangular parallelepipeds by edge flaking their long edges with Rockwell and Vickers indenters (EF method) and by scratching the specimen surface with a Rockwell indenter followed by flaking its edge (S+EF method). It was established that the fracture of those glass specimens in their edge flaking with a Rockwell indenter was started with the formation of a Hertzian ring crack and their corresponding chip scars had the form of Hertzian "quasi-cones." Fractographic data were used in analysis of test results.Introduction. One can hardly find any field of human activities where silicate glasses are not in use. Despite brittleness and inconsiderable deformability inherent in such materials, they turn out indispensable for many technical and other fields of application. This gives impetus to studies on the mechanical behavior of those materials and, in particular on their ability to resist fracture. Their fracture toughness was evaluated by different methods, including fracture of the specimen surface with sharp and blunt indenters [1]. As a result, a great body of experimental data was accumulated, which contributed to the enhancement of glass capabilities and to the gain in reliability of glass items in operation.As was mentioned earlier [2], glass is a material very complicated for comprehension. Its fracture behavior is still not clearly understood, and the choice of an optimum method for determining its fracture resistance is unresolved as yet. Therefore, the investigation of glass fracture in flaking the edges of rectangular parallelepipeds with standard indenters was carried out, which turned out to be an effective approach to studying different ceramics and allowed new information on their behavior under loading to be obtained [3].Materials and Methods. This investigation was targeted for getting the general notion of glass behavior in its edge flaking. For this purpose the two types of glass varying in their compositions were taken: "normal" (silica contents are less than 70-75%) and "anomalous", i.e., containing up to 99.9% silica [4]. The mechanical behavior of the former is believed to be similar to the behavior of other brittle materials, while glass of the second type exhibits certain differences associated with its structure. Therefore, both technical quartz glass, containing about 90-95% silica doped with Na 2 O and Al 2 O 3 , and normal window glass with about 72% silica were studied. Experiments were also performed on industrial hardened sheet glass. Those glasses were manufactured commercially, thus, their correct compositions, being "know-how" of enterprises, are unknown.The tests made use of specimens in the form of polished rectangular beams of standard sizes (3 4 × -mm