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The paper is devoted to the development of the mesoscopic mechanical model of porous silica refractory ceramics. The model takes into account the complex morphology of pore structure (channel-type pores and closed round pores) and pore size distribution within several orders of magnitude. Large (mesoscopic) pores are considered explicitly, while small (microscopic) pores concentrated near the interfaces between fine grains are effectively modelled as planar defects in the skeleton. The model was implemented within the numerical method of homogeneously deformable discrete elements. Using computer simulation, we studied the influence of the porosity value on the elastic and strength characteristics of representative volume elements (mesoscopic samples) of refractory. An analysis of the simulation results showed that microscopic defects have a significant influence on the mechanical behavior and macroscopic mechanical properties of the refractory, although the volume fraction of microscopic porosity is insignificant. [ABSTRACT FROM AUTHOR]

The metal-ceramic composite Ti/(ZrB2–15 vol % SiC) was obtained by pressure sintering at 1300°C from metallic titanium and ceramics. The formation of an intermediate layer with a complex gradient microstructure in which there are five layers with different phase composition, microstructure type, and grain size has been established in this material. X-ray studies showed that the phase composition of the composite is represented by hexagonal modifications of Ti, ZrB2, cubic syngony of SiC and MAX-phase Ti3SiC2 with a hexagonal structure. The formed intermediate layer provides high adhesion between the metal and ceramic layers. [ABSTRACT FROM AUTHOR]

The structure and properties of ceramic composites based on zirconium dioxide with the addition of carbon nanotubes have been studied. It is shown that introduction of carbon nanotubes leads to insignificant increase of Young's modulus and hardness of ZrO2–CNT ceramics. It is shown that the increase of fracture toughness in ZrO2–CNT composites is provided by synergistic manifestation of mechanisms increasing crack propagation work. Several mechanisms of energy dissipation are realized in ZrO2–CNT ceramic composites, namely phase transition of tetragonal to monocline modification of ZrO2 and bridging of cracks by carbon nanotubes. It is worth noting that the contribution of martensitic transformation to crack resistance decreases as the volume fraction of carbon nanotubes in the zirconia matrix increases, which is caused by a decrease in the grain size of the tetragonal zirconium dioxide phase and thus with its transition to a stable state. [ABSTRACT FROM AUTHOR]

The porous ZrO2-MgO composites were studied. The influence of the composition and sintering time on the grain size, porosity and pore sizes changes kinetics were studied. The fractal dimension of the fracture surface was determined by the method of vertical cross sections on SEM images. The kinetics of a change in the average size of micro- and macropores showed that with the sintering time increasing the system desire to form a unimodal pore structure due to volume shrinkage and pores coalescence. It was shown that changes of the fractal dimension reflect the stages of porous ZrO2-MgO composite solid-phase sintering. The maximum value of the fractal dimension, 1.5, is reached at the transition from the first to the second stage of solid-phase sintering and is observed at the ratio of macro- and micropores 12.5, which indicates the formation of the most developed surface. [ABSTRACT FROM AUTHOR]

The structure and defects self-healing mechanism of ceramic composite materials (ZrB2-ZrC-SiC)-ZrO2 depending on the volume fraction of zirconia (0, 5, 10, 15 vol.%) werestudied. Increasing of ZrO2 content led to higher composites compaction obtained by sintering under a pressure of 30 MPa at a temperature of 1900 °C, and to decreasing of the ceramic particles average size. Annealing in the air at 1200 °C led to (ZrB2-ZrC-SiC)-ZrO2 composites oxidation with the formation of an oxide layer consisting of a porous ZrO2 matrix impregnated with borosilicate (B2O3 + SiO2) glass. The thickness of the oxide layer increased with the increasing of zirconia volume fraction. The percentage of defects self-healing after °C led to the complete defects healing with ZrO2 content above 10 vol. %. The effect of temperature of 1600 °C on ceramic composites led to the complete defects healing, regardless of the ZrO2 content. [ABSTRACT FROM AUTHOR]

Porous ceramics ZrO2−MgO with a 50 vol. % pore volume and bimodal pore size distribution were studied. The samples were produced by cold uniaxial pressing followed by sintering at temperature of 1600°C and a holding time from 10 min to 10 hours. Bimodal pore structure was obtained by adding of ultrahigh molecular weight polyethylene pore-forming particles with average size 50 µm to the initial powder mixtures. The pore volume for all samples was constant—50±3 vol. %. With increasing of sintering holding time the average size of the macropores decreased and the micropores increased. The coherent diffraction domains average size of components increases with increasing of MgO concentration and the time of the sintering, while the microdistortions of crystal lattice decrease. With an increase of the sintering holding time more than 5 hours, an insufficient stabilization of cubic ZrO2 takes place for the low MgO concentrations. The dependences of the tensile strength and the Young’s modulus on the microstresses in the ceramic composite structure are investigated. Estimation of the microstresses on the basis of X-ray diffraction analysis has shown that the tensile strength mainly determined by microstresses and its increasing leads to a strength decrease. [ABSTRACT FROM AUTHOR]

The influence of mechanical activation of a nanocrystalline ZrO2 (3 wt. % of MgO) powder on its structure is studied. For mechanical activation a ball mill was used with a constant speed of 70 rpm. The duration of treatment was from 1 to 50 hours. It is shown that after mechanical activation of the powder for 5 hours, it begins aggregation of particles. A further treatment leads to the separation of particles into two fractions. After 25 hours of mechanical activation there was a complete breakdown of the aggregates and reaching a minimum of the particle average size in comparison with the initial powder. Further increasing of the activation duration did not lead to a noticeable decrease in the average size of individual particles, however, the morphology of the powder changed, and the particles began to group into large spherical formations. [ABSTRACT FROM AUTHOR]

The highly dispersed ZrO2Y2O3 (3 mol. %) powder compaction process was studied at a pressure range from 20 to 300 MPa. The dependences of compacts volume, the average particle size and the relative density of the samples and the monoclinic phase amount of zirconia on the pressure value were studied. It was shown that the most intensive powder structural elements destruction occurred in the pressure range from 50 to 100 MPa. This is confirmed by zirconia powder monoclinic phase increasing diagram, which is not monotonous during pressing. The minimum particle size was 0.15 μm, which is three times less than in the initial powder, and achieved at the pressure value of 300 MPa. [ABSTRACT FROM AUTHOR]