Study of the microstructure of ceramic matrix composites in the SiC - C<Subscript>f</Subscript> system

Results of a study of the microstructure of ceramic matrix composites (CMC) in the SiC - C_f system with high crack resistance and strength tested under conditions of unidirectional infiltration of molten high-purity silicon by methods of electron and optical microscopy and fractography are reported.__________Translated from Novye Ogneupory, No. 10, pp. 41 – 46, October, 2004.     

Mechanical properties of structural ceramic materials based on silicon nitride

The creation of structural ceramic materials based on silicon nitride is considered. The results of a study of the properties of these materials in a wide temperature range are presented, including data on the short-term strength, elastic characteristics, and parameters of fracture mechanics and results of long-term static and dynamic tests of some silicon nitride materials.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 14–17, November, 1996.     

Microwave sintering of silicon nitride-based ceramics

A silicon nitride-based ceramics (97% of the theoretical density, a bending strength limit of up to 700 MPa) is obtained using a microwave sintering method. The procedure of microwave sintering is 7–9 times shorter than the usual sintering process and requires lower temperatures 100–150°C. The material obtained exhibits a highly disperse microstructure and a high content of α-Si₃N₄ phase. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 11–13, January, 1997.     

Silicon nitride structural ceramics with an elevated strength at 1300°C

A high-temperature ceramics based on Si₃N₄ with an ultimate bending strength of 620 MPa at room temperature and 450 MPa at 1300°C has been developed using hot pressure casting and compression sintering. The ceramics is characterized by a high degree of crystallization of the intergrain phase and the presence of high-temperature 3Y₂O₃·5Al₂O₃ garnet in the phase composition. The microstructure of the ceramics is represented mainly by irregular grains with a maximum size of 12 μm and inclusions of elongated hexagonal crystals of Si₃N₄. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 20–24, June, 1997.     

Preparation of Dense Ceramics Based on Silicon Nitride Nanopowders

Synthesis of ceramics from silicon nitride nanopowders using hot-pressing and pressure-assisted and microwave (MW) sintering techniques has been studied. Dense ceramics with improved physicomechanical characteristics can be prepared on condition that most of the oxygen in the form of silicon monoxide (contained at 5 – 8 wt.% in the precursor powders) has been removed from the material. In ceramics treated by the three sintering technologies, an extensive grain growth is observed. The microstructure of these materials was more disperse in comparison with that of ceramic prepared from conventional -Si₃N₄ powders synthesized in a furnace. This provides a route towards preparing nanopowder-based ceramics with a 25 – 30% increase in strength in comparison to ceramics of the same density prepared from conventional powders.     

CEramics based on α-sialon

Ceramics containing pure α-sialon and α-sialon in combination with β-Si₃N₄, produced from two types of silicon nitride powder, are described. It is shown that the high-temperature strength of the ceramics increases with increase in the content of α-sialon in the composition. Data on the microstructure, phase composition, and mechanical characteristics of the synthesized materials are presented.     

Some distinctive features of structure formation in materials based on sintered silicon nitride

Special features of formation of the microstructure and phase composition of sintered materials based on Si₃N₄ and α-sialons synthesized in the Si - Y - Al - O - N system by the method of compressive and microwave sintering are described. It is concluded that the morphology of the initial Si₃N₄ powders, the phase composition of the initial mixture, and the sintering technology of the ceramics in the decisive stage determine its microstructure, including the processes of self-reinforcement by β-Si₃N₄ crystals, the phase composition, and the physicomechanical characteristics. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 7, pp. 28 – 31, July, 2000.     

A Study of the Wear in Ceramic Bearings by a Thin-Layer Activation Method

The wear resistance of ceramic sliding bearings fabricated from sintered Si₃N₄ and ZrO₂ is studied by the thin-layer activation method. Radioisotopic tags were applied by exposing the ceramic components to a proton beam with an energy of 7.6 MeV. Exposure conditions are specified to avoid radiative damage of the surface of ceramic components. The wear under dry-friction conditions was determined by radiometry of the isotopically labeled surface using calibration curves. The running-in time was found to be about 400 min for Si₃N₄-based and 500 – 600 min for ZrO₂-based components, with wear rates of 4 – 5 and 5 – 6 , respectively. The data obtained attest to the high performance characteristics of the ceramic bearings that are used for submersible pumps for pumping crude oil out of wells.