S. N. Kul’kov

The non-Hooke’s behavior of porous zirconia subjected to high-rate compressive deformation

The deformation of partially stabilized zirconia ZrO2(Y2O3) with various pore morphologies is studied. During the synthesis of bar and lamellar ceramic structures, an effect of mechanical instability is discovered. This effect, along with the purely elastic behavior of the ceramic and the accumulation of microdamages under high-rate compressive deformation, produces considerable strains in the porous structure without material failure and substantially extends the applications of porous ceramic materials.

Synthesis, structure, and phase composition of Al-Al4C3 nanostructured materials

The morphology and phase composition of nanocrystalline powders of aluminum and carbon in the form of cluster diamonds are investigated. It is found that the hot compaction of the C-Al powder mixture is accompanied by the formation of an Al4C3 phase that has a highly disperse structure. The average crystallite size in hot-compacted materials is 40 nm for the metal matrix and 30 nm for aluminum. It is shown that as the carbon fraction in the initial powder mixture rises, the volume of the threshold space in hot-compacted materials increases.

Mechanical behavior of porous zirconium dioxide under active deformation by compression

The properties of the mechanical behavior of porous ceramic based on partially stabilized zirconium dioxide are studied. The special features of the mechanical behavior of ceramic with different degrees of porosity are determined. It is shown that three macrodeformation mechanisms are observed simultaneously in the material: elastic deformation characteristic of compact material; microcracking with accumulation of microdefects; and displacement of local volumes of material into the pore space. A ceramic with porosity less than 20% retains its capacity for transformational changes in the stress field of a propagating crack.

Percolation transitions in porous structure and their effect on physicochemical properties of ceramics

Computer simulation and experimental investigation of zirconia-based ceramics showed that a percolation transition from isolated to communicating pores in this brittle porous material lead to changes in the character of dependence of the elastic properties and structural characteristics on the total porosity.

Effect of mechanical processing of ultrafine ZrO2 + 3 wt % MgO powder on the microstructure of ceramics produced from it

This paper examines the effect of milling on the morphology and properties of ultrafine ZrO2 + 3 wt % MgO powder and on the microstructure and strength of the ceramics produced from it. Low-energy milling enables a marked decrease in the degree of aggregation of the powder, which in turn reduces the grain size and increases the density and strength of the ceramics.

Texture formation on the friction surface in transformation-toughened ceramics

The surface of Y-TZP ceramics after dry friction on steel in a wide range of relative sliding velocities (0.2–11.1 m/s) was studied by X-ray diffraction. An analysis of the surface structure showed that the texture state of the friction surface is similar to that observed for analogous materials upon rough grinding. The main trends in the I(002)/I(200) intensity ratio characterizing the tetragonal ZrO2 phase as a function of the sliding velocity and the ceramic grain size are established. The mechanisms of lattice reorientation operative at various sliding velocities are discussed.

A possible method of computer-aided design of materials with a highly porous matrix structure based on the method of moving cellular automata

The method of moving cellular automata was used to model a sample of ZrO2 ceramic with a matrix structure under conditions of uniaxial compression. Studies were made of the strength and type of damage to the initial structure and its modifications. Particular attention was devoted to studying the influence of characteristics of the matrix structure on the formation and suppression of internal stress macroconcentrators. It is shown that the method of moving cellular automata can be used for the computer-aided design of matrix materials with a complex structure by specifically influencing the formation and evolution of stress macroconcentrators.

Friction and wear of Y-TZP and Y-TZP-Al2O3 ceramics in high-speed sliding on steel

The processes of wear of tetragonal zirconia-based ceramics partially stabilized with yttrium oxide (Y-TZP) are studied during dry high-speed sliding in pin-on-disk pairs at sliding velocities up to 47 m/s. It is shown that these wear tests produce tribolayers of intricate composition on the surface of the Y-TZP and Y-TZP-Al2O3 ceramic materials, inducing nonmonotonous wear-rate changes. The normal wear changes into disastrous highly intensive wear at the first stage when the sliding accelerates (from 0.1 to 4 m/s). At the second stage (in the velocity range from 6 to 47 m/s) the wear rate drops almost to its initial value, typical of slow sliding velocities (0.1 m/s). In this velocity range, the friction of the Y-TZP and Y-TZP-Al2O3 ceramics is almost wearless.

Inelastic behavior of ceramics with hierarchical pore structure under compression

The compaction behavior is studied in Al2O3 ceramics with a pore space volume in the range from 35 to 60% and with the following three types of hierarchical pore structure: coarse porosity with a size of 80 to 100 μm, fine porosity with a size of 14 to 15 μm, and intermediate interblock porosity comprised of elongated (110–120 μm) porous microchannels formed as a result of zonal isolation during sintering. It is shown that the obtained hierarchical porous structure causes the formation of a hierarchical deformation structure in the volume of ceramics and leads to a decrease in the extent of destruction processes from the macroscopic scale in the case of unimodal ceramics to the microscale destruction comparable with the sizes of the blocks formed during sintering.

Structural transformations in nanocrystalline zirconium dioxide

Peculiar features of the phase composition and structure of nanocrystalline powders based on zirconium dioxide, which appear during heating, have been studied. The oscillation of lattice microdistortions has been found, which is caused by variation in the crystallite defect structure. The phase composition of this material is determined according to the level of microdistortions.