The Experts below are selected from a list of 153 Experts worldwide ranked by ideXlab platform

Toshihiro Ishikawa - One of the best experts on this subject based on the ideXlab platform.

  • SiC polycrystalline fibre and its fibre-bonded ceramic
    Annales de Chimie: Science des Materiaux, 2000
    Co-Authors: Toshihiro Ishikawa
    Abstract:

    A type of SiC polycrystalline fibre (SA fibre) obtained by sintering an amorphous Si-Al-C-O fibre precursor at 1900°C in Argon atmosphere is described. A sintered SiC fibre-bonded ceramic (SA-Tyrannohex), which was synthesized by hot-pressing piled sheets of the amorphous Si-Al-C-O fibre precursor prepared from an organosilicon polymer, is also introduced. The former, SA fibre, which contains a very small amount of aluminium, has a high tensile strength and modulus, and shows no degradation of strength or change in composition on heating up to 2000°C in inert atmosphere and up to 1000°C in air for a time longer than 2000 hours. Moreover, SA fibre shows better high-temperature creep resistance in air at 1300°C than commercial counterparts. We also found that the mechanical properties of the fibre were markedly improved by a decrease in the fibre diameter. On the other hand, the latter, SA-Tyrannohex, consists of a highly ordered, close-packed structures of very fine hexagonal columnar fibres with a thin interfacial carbon layer. The interior of the fibre element was composed of sintered SiC crystals. This material shows high strength, Fibrous Fracture behaviour, excellent high-temperature properties, and high thermal conductivity (even at temperatures over 1000°C). It was also found that the initial strength of the SA-Tyrannohex, which was prepared from thinner starting fibre, was perfectly preserved up to 1700°C in air.

  • A Tough, Thermally Conductive Silicon Carbide Composite with High Strength up to 1600°C in Air
    Science (New York N.Y.), 1998
    Co-Authors: Toshihiro Ishikawa, Kenji Matsunaga, Shinji Kajii, Yasuhiko Kohtoku, Toshihiko Hogami, Toshio Nagasawa
    Abstract:

    A sintered silicon carbide fiber-bonded ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar fibers with a thin interfacial carbon layer between fibers, was synthesized by hot-pressing plied sheets of an amorphous silicon-aluminum-carbon-oxygen fiber prepared from an organosilicon polymer. The interior of the fiber element was composed of sintered beta-silicon carbide crystal without an obvious second phase at the grain boundary and triple points. This material showed high strength (over 600 megapascals in longitudinal direction), Fibrous Fracture behavior, excellent high-temperature properties (up to 1600 degreesC in air), and high thermal conductivity (even at temperatures over 1000 degreesC).

  • Structure and properties of Si-Ti-C-O fibre-bonded ceramic material
    Journal of Materials Science, 1995
    Co-Authors: Toshihiro Ishikawa, Kenji Matsunaga, Shinji Kajii, T. Hogami, Yasuhiko Kohtoku
    Abstract:

    Si-Ti-C-O fibre-bonded ceramic material was synthesized from pre-oxidized Si-Ti-C-O fibre with an oxide layer 400–600 nm thick, by hot-pressing at 2023 K under 50–70 MPa. The interstices in the Si-Ti-C-O fibre-bonded ceramic material were packed with an oxide material which existed on the surface of the pre-oxidized Si-Ti-C-O fibre, and the oxide material formed a small amount of the matrix phase (⩽10 vol%). At the fibre-matrix interface, aligned turbostratic carbon, which was oriented around the fibre, was formed during hot-pressing. The existence of the interfacial carbon layer indicated the Si-Ti-C-O fibre-bonded ceramic material to have a Fibrous Fracture pattern with high Fracture energy. The Si-Ti-C-O fibre-bonded ceramic material showed excellent durability even at 1773 K in air, because a protective oxide layer is formed on the surface at a high temperature (above 1273 K) in air. Moreover, the Si-Ti-C-O fibre-bonded ceramic material almost maintained its initial strength in the bending and tensile tests, even at 1773 K in air.

  • A new type of fiber-bonded-ceramic material synthesized from pre-oxidized Si-Ti-C-O fiber
    Advanced Performance Materials, 1994
    Co-Authors: Shinji Kajii, Toshihiro Ishikawa, Kenji Matsunaga, Yasuhiko Kohtoku
    Abstract:

    Two types of fiber-bonded-ceramic material (FBC_2123 or FBC_1873) were synthesized from preoxidized Si-Ti-C-O fibers with oxide layers of 150 to 500 nm in thickness at 2123 K or 1873 K under 50 to 70 MPa. The interstices in both types of the materials were packed by an oxide material, which had existed on the surface of the pre-oxidized Si-Ti-C-O fiber. So, the dense, fiber-bonded-ceramic materials with small amount of the oxide matrix were obtained. During hot-pressing, carbon in excess of the non-stoichiometric ratio was released from the fiber and formed an interfacial layer on the surface of the fiber, beneath the pre-existing oxide material. Both FBC_2123 and FBC_1873 showed Fibrous Fracture patterns with high Fracture energies at temperatures up to 1573 K and 1773 K, respectively. FBC_2123 exhibited some plasticity in air at a temperature of 1673 K or over, due to the existence of amorphous silica in the matrix, and then a reduction in bending strength was observed at 1773 K in air. On the other hand, FBC_1873 maintained its initial bending strength up to 1773 K in air, which is attributed to reduced crystallization of Si-Ti-C-O fiber and to the formation of cristobalite in the matrix.

  • 24th Annual Conference on Composites, Advanced Ceramics, Materials, and Structures: B: Ceramic Engineering and Science Proceedings, Volume 21, Issue 4 - High heat-resistant SiC-polycrystalline fibre and its fibre-bonded ceramic
    24th Annual Conference on Composites Advanced Ceramics Materials and Structures: B: Ceramic Engineering and Science Proceedings Volume 21 Issue 4, 1
    Co-Authors: Toshihiro Ishikawa
    Abstract:

    Here we describe a type of SiC polycrystalline fibre (SA fibre) obtained by sintering an amorphous Si-Al-C-O fibre precursor at 1900°C in Ar atmosphere. Furthermore, we also explain a sintered SiC fibre-bonded ceramic (SA-Tyrannohex), which was synthesized by hot-pressing piled sheets of the amorphous Si-Al-C-O fibre precursor prepared from an organosilicon polymer. The former SA fibre with high strength showed no reduction in strength on heating to 2000°C in inert atmosphere. This fibre also showed excellent creep resistance in air, high thermal conductivity and good weave-ability. The latter SA-Tyrannohex consisted of highly ordered, close-packed structures of very fine hexagonal columnar fibres with a thin interfacial carbon layer. The interior of the fibre element was composed of sintered SiC crystal. This material with high strength showed Fibrous Fracture behaviour, high thermal conductivity and excellent high-temperature strength up to 1700°C.

Yasuhiko Kohtoku - One of the best experts on this subject based on the ideXlab platform.

  • A Tough, Thermally Conductive Silicon Carbide Composite with High Strength up to 1600°C in Air
    Science (New York N.Y.), 1998
    Co-Authors: Toshihiro Ishikawa, Kenji Matsunaga, Shinji Kajii, Yasuhiko Kohtoku, Toshihiko Hogami, Toshio Nagasawa
    Abstract:

    A sintered silicon carbide fiber-bonded ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar fibers with a thin interfacial carbon layer between fibers, was synthesized by hot-pressing plied sheets of an amorphous silicon-aluminum-carbon-oxygen fiber prepared from an organosilicon polymer. The interior of the fiber element was composed of sintered beta-silicon carbide crystal without an obvious second phase at the grain boundary and triple points. This material showed high strength (over 600 megapascals in longitudinal direction), Fibrous Fracture behavior, excellent high-temperature properties (up to 1600 degreesC in air), and high thermal conductivity (even at temperatures over 1000 degreesC).

  • Structure and properties of Si-Ti-C-O fibre-bonded ceramic material
    Journal of Materials Science, 1995
    Co-Authors: Toshihiro Ishikawa, Kenji Matsunaga, Shinji Kajii, T. Hogami, Yasuhiko Kohtoku
    Abstract:

    Si-Ti-C-O fibre-bonded ceramic material was synthesized from pre-oxidized Si-Ti-C-O fibre with an oxide layer 400–600 nm thick, by hot-pressing at 2023 K under 50–70 MPa. The interstices in the Si-Ti-C-O fibre-bonded ceramic material were packed with an oxide material which existed on the surface of the pre-oxidized Si-Ti-C-O fibre, and the oxide material formed a small amount of the matrix phase (⩽10 vol%). At the fibre-matrix interface, aligned turbostratic carbon, which was oriented around the fibre, was formed during hot-pressing. The existence of the interfacial carbon layer indicated the Si-Ti-C-O fibre-bonded ceramic material to have a Fibrous Fracture pattern with high Fracture energy. The Si-Ti-C-O fibre-bonded ceramic material showed excellent durability even at 1773 K in air, because a protective oxide layer is formed on the surface at a high temperature (above 1273 K) in air. Moreover, the Si-Ti-C-O fibre-bonded ceramic material almost maintained its initial strength in the bending and tensile tests, even at 1773 K in air.

  • A new type of fiber-bonded-ceramic material synthesized from pre-oxidized Si-Ti-C-O fiber
    Advanced Performance Materials, 1994
    Co-Authors: Shinji Kajii, Toshihiro Ishikawa, Kenji Matsunaga, Yasuhiko Kohtoku
    Abstract:

    Two types of fiber-bonded-ceramic material (FBC_2123 or FBC_1873) were synthesized from preoxidized Si-Ti-C-O fibers with oxide layers of 150 to 500 nm in thickness at 2123 K or 1873 K under 50 to 70 MPa. The interstices in both types of the materials were packed by an oxide material, which had existed on the surface of the pre-oxidized Si-Ti-C-O fiber. So, the dense, fiber-bonded-ceramic materials with small amount of the oxide matrix were obtained. During hot-pressing, carbon in excess of the non-stoichiometric ratio was released from the fiber and formed an interfacial layer on the surface of the fiber, beneath the pre-existing oxide material. Both FBC_2123 and FBC_1873 showed Fibrous Fracture patterns with high Fracture energies at temperatures up to 1573 K and 1773 K, respectively. FBC_2123 exhibited some plasticity in air at a temperature of 1673 K or over, due to the existence of amorphous silica in the matrix, and then a reduction in bending strength was observed at 1773 K in air. On the other hand, FBC_1873 maintained its initial bending strength up to 1773 K in air, which is attributed to reduced crystallization of Si-Ti-C-O fiber and to the formation of cristobalite in the matrix.

Gyan Shankar - One of the best experts on this subject based on the ideXlab platform.

  • On the role of precipitates in controlling microstructure and mechanical properties of Ag and Sn added 7075 alloys during artificial ageing
    Materials Science and Engineering: A, 2018
    Co-Authors: Abhishek Ghosh, Manojit Ghosh, Gyan Shankar
    Abstract:

    Abstract Tailoring size, density and nature of precipitates by ageing and alloy additions and subsequent correlation with microstructure and mechanical properties for 7075 alloys was investigated in current research. The effect of the minor addition of Ag and Sn in 7075 base alloy has been revealed using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The hardness and tensile testing were carried out as a part of mechanical properties evaluation. Under peak age condition (T6), even a minor addition of Ag and Sn was found to decrease the average grain size and impart uniformity in the pattern of the dispersed intermetallic phases in the matrix compared to base 7075 alloy. The enhancement of precipitation kinetics owing to the addition of Ag and Sn in AA 7075 has been confirmed by the results obtained from DSC. Johnson-Mehl-Avramani (JMA) equation was used to calculate the amount of precipitates, its kinetics of formation and activation energies of each phase at different temperatures. It demonstrated that activation energies of phases (GP zone dissolution and η′) for Ag bearing alloy were decreased which suggested that Ag possessed a positive effect on the early decomposition of GP zone and η′ precipitates. In the effort to explain the higher strength and ductility with Ag and Sn added alloys, the microstructural attributes in the form of generation of more heterogeneous nucleation sites coupled with a high density of fine η′ precipitation throughout in the matrix, observed through TEM investigation, was accounted responsible. The average interparticle spacing among the η′ precipitates was found lowest in Ag containing alloys which have a beneficial effect on improvement of mechanical properties. Fracture surfaces revealed transgranular type which occurred by propagating the cracks through the grains. Fine equiaxed dimples were present inside the surface of the Fibrous Fracture surfaces suggesting appreciable ductility for all peak aged alloys. Finer dimples were observed in Ag containing alloys due to its fine grain size.

Abhishek Ghosh - One of the best experts on this subject based on the ideXlab platform.

  • On the role of precipitates in controlling microstructure and mechanical properties of Ag and Sn added 7075 alloys during artificial ageing
    Materials Science and Engineering: A, 2018
    Co-Authors: Abhishek Ghosh, Manojit Ghosh, Gyan Shankar
    Abstract:

    Abstract Tailoring size, density and nature of precipitates by ageing and alloy additions and subsequent correlation with microstructure and mechanical properties for 7075 alloys was investigated in current research. The effect of the minor addition of Ag and Sn in 7075 base alloy has been revealed using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The hardness and tensile testing were carried out as a part of mechanical properties evaluation. Under peak age condition (T6), even a minor addition of Ag and Sn was found to decrease the average grain size and impart uniformity in the pattern of the dispersed intermetallic phases in the matrix compared to base 7075 alloy. The enhancement of precipitation kinetics owing to the addition of Ag and Sn in AA 7075 has been confirmed by the results obtained from DSC. Johnson-Mehl-Avramani (JMA) equation was used to calculate the amount of precipitates, its kinetics of formation and activation energies of each phase at different temperatures. It demonstrated that activation energies of phases (GP zone dissolution and η′) for Ag bearing alloy were decreased which suggested that Ag possessed a positive effect on the early decomposition of GP zone and η′ precipitates. In the effort to explain the higher strength and ductility with Ag and Sn added alloys, the microstructural attributes in the form of generation of more heterogeneous nucleation sites coupled with a high density of fine η′ precipitation throughout in the matrix, observed through TEM investigation, was accounted responsible. The average interparticle spacing among the η′ precipitates was found lowest in Ag containing alloys which have a beneficial effect on improvement of mechanical properties. Fracture surfaces revealed transgranular type which occurred by propagating the cracks through the grains. Fine equiaxed dimples were present inside the surface of the Fibrous Fracture surfaces suggesting appreciable ductility for all peak aged alloys. Finer dimples were observed in Ag containing alloys due to its fine grain size.

Shinji Kajii - One of the best experts on this subject based on the ideXlab platform.

  • A Tough, Thermally Conductive Silicon Carbide Composite with High Strength up to 1600°C in Air
    Science (New York N.Y.), 1998
    Co-Authors: Toshihiro Ishikawa, Kenji Matsunaga, Shinji Kajii, Yasuhiko Kohtoku, Toshihiko Hogami, Toshio Nagasawa
    Abstract:

    A sintered silicon carbide fiber-bonded ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar fibers with a thin interfacial carbon layer between fibers, was synthesized by hot-pressing plied sheets of an amorphous silicon-aluminum-carbon-oxygen fiber prepared from an organosilicon polymer. The interior of the fiber element was composed of sintered beta-silicon carbide crystal without an obvious second phase at the grain boundary and triple points. This material showed high strength (over 600 megapascals in longitudinal direction), Fibrous Fracture behavior, excellent high-temperature properties (up to 1600 degreesC in air), and high thermal conductivity (even at temperatures over 1000 degreesC).

  • Structure and properties of Si-Ti-C-O fibre-bonded ceramic material
    Journal of Materials Science, 1995
    Co-Authors: Toshihiro Ishikawa, Kenji Matsunaga, Shinji Kajii, T. Hogami, Yasuhiko Kohtoku
    Abstract:

    Si-Ti-C-O fibre-bonded ceramic material was synthesized from pre-oxidized Si-Ti-C-O fibre with an oxide layer 400–600 nm thick, by hot-pressing at 2023 K under 50–70 MPa. The interstices in the Si-Ti-C-O fibre-bonded ceramic material were packed with an oxide material which existed on the surface of the pre-oxidized Si-Ti-C-O fibre, and the oxide material formed a small amount of the matrix phase (⩽10 vol%). At the fibre-matrix interface, aligned turbostratic carbon, which was oriented around the fibre, was formed during hot-pressing. The existence of the interfacial carbon layer indicated the Si-Ti-C-O fibre-bonded ceramic material to have a Fibrous Fracture pattern with high Fracture energy. The Si-Ti-C-O fibre-bonded ceramic material showed excellent durability even at 1773 K in air, because a protective oxide layer is formed on the surface at a high temperature (above 1273 K) in air. Moreover, the Si-Ti-C-O fibre-bonded ceramic material almost maintained its initial strength in the bending and tensile tests, even at 1773 K in air.

  • A new type of fiber-bonded-ceramic material synthesized from pre-oxidized Si-Ti-C-O fiber
    Advanced Performance Materials, 1994
    Co-Authors: Shinji Kajii, Toshihiro Ishikawa, Kenji Matsunaga, Yasuhiko Kohtoku
    Abstract:

    Two types of fiber-bonded-ceramic material (FBC_2123 or FBC_1873) were synthesized from preoxidized Si-Ti-C-O fibers with oxide layers of 150 to 500 nm in thickness at 2123 K or 1873 K under 50 to 70 MPa. The interstices in both types of the materials were packed by an oxide material, which had existed on the surface of the pre-oxidized Si-Ti-C-O fiber. So, the dense, fiber-bonded-ceramic materials with small amount of the oxide matrix were obtained. During hot-pressing, carbon in excess of the non-stoichiometric ratio was released from the fiber and formed an interfacial layer on the surface of the fiber, beneath the pre-existing oxide material. Both FBC_2123 and FBC_1873 showed Fibrous Fracture patterns with high Fracture energies at temperatures up to 1573 K and 1773 K, respectively. FBC_2123 exhibited some plasticity in air at a temperature of 1673 K or over, due to the existence of amorphous silica in the matrix, and then a reduction in bending strength was observed at 1773 K in air. On the other hand, FBC_1873 maintained its initial bending strength up to 1773 K in air, which is attributed to reduced crystallization of Si-Ti-C-O fiber and to the formation of cristobalite in the matrix.