N. L. Savchenko

Vacuum sintering of a ceramic based on zirconium dioxide

The results of a study of the phase composition and mechanical properties of a ceramic based on ZrO2-Y2O3 after vacuum sintering of powders with complex morphology in a wide range of temperatures and sintering holding times are reported. Dense ceramic materials with high mechanical properties were obtained.

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.

High temperature vacuum sintering of plasmochemical powders based on ZrO2

The phase composition and mechanical properties of ZrO2-based ceramics prepared by sintering plasmochemical powders of complex morphology in air and in vacuum were compared. Sintering at a high temperatures in vacuum produced material exhibiting high density and good mechanical properties, in which the zirconium dioxide was entirely in the tetragonal form.

Behavior of the submicrocrystalline Y–TZP–Al2O3 composite in dry friction with steel

The paper discusses the wear resistance, friction coefficient, and structure of friction surfaces of submicron crystalline Y–TZP–Al2O3 composite rubbed against a steel disk counterface at a pressure of 5 MPa in a range of sliding speeds from 1 to 20 m/sec. It is shown that, starting at 2 m/sec, the friction surface is subdivided by a crack network into separate regions within which local spalling occurs at the maximum wear rate and a sliding speed of 5 m/sec. X-ray diffraction reveals inversion (with respect to the initial state) of the peak intensities of the tetragonal phase with random crystalline grain orientation. The degree of this inversion increases with sliding speed. These results are discussed in terms of the effects exerted by the reorientation of martensite-free deformation twins in the tetragonal phase and the formation of a quasi-liquid film on the wear resistance of Y–TZP–Al2O3.

Vacuum sintering of plasmochemical powders based on ZrO2. 1. Effect of sintering temperature on properties of ceramics

Powders produced by thermal dissociation of metals dispersed from droplets of salt solutions in the plasma of arc or high-frequency dischage have often a complicated morphology (hollow spheres, flakes). This complicates production from these powders of dense ceramic parts based on ZrO{sub 2} - Y{sub 2}O{sub 3} hardened by martensitic transformation. The main special feature of producing these materials is that at the temperature of conventional sintering in air higher than 1600{degrees}C required for obtaining high density the grains start to grow and this leads to the T{yields}M transformation in cooling which fractures the specimens. It was shown that sintering the plasmochemical zirconia, stabilizes 3% (mol) Y{sub 2}O{sub 3}, in vacuum at 1800{degrees}C makes it possible to avoid destabilizing T-ZrO{sub 2} in cooling and produce a dense and strong material. The aim of this work was to examine the properties based on zirconia, partially stabilized with Y{sub 2}O{sub 3}, after vacuum sintering in a wide temperature range up to 1750{degrees}C.

Combined mechanism for the hardening of a ZrO2-Y2O3 ceramic

The phase composition and mechanical properties have been examined for a ZrO2-Y2O3 ceramic having a combined hardening mechanism, which was made by high-temperature sintering under vacuum. The mechanism enables one to alter the properties of the zirconium dioxide base ceramic substantially. The material has a combination of high strength and toughness because of the high viscosity of the untransformed part of the material, which produces an additional strengthening effect along with the transformational hardening.

Phase composition and mechanical properties of a zirconium dioxide based ceramic obtained by high temperature sintering in a vacuum

Changes in phase composition and mechanical properties of sintered ZrO2 + 3% (mole) Y2O3 specimens were examined after annealing in air and after various mechanical operations. Compacted ceramic specimens containing T and T′ phase were obtained by sintering in a vacuum at 1800°C. Ceramics containing T and T′ phases have excellent toughness (K1c up to 15 MPa·m1/2), bend strength up to 800 MPa and HV hardness up to 13 GPa.