Provided is a method for producing an inorganic fiber-bonded ceramic material, which can produce, at a high yield, an inorganic fiber-bonded ceramic material with fewer defects, and with an end part and a central part equivalent to each other in microstructure and mechanical properties, and also makes it possible to increase the ceramic material in size. The method for producing an inorganic fiber-bonded ceramic material is characterized in that it includes: a first pressing step of setting, in a carbon die, a laminate to be surrounded by a ceramic powder, the laminate obtained by stacking a coated inorganic fiber shaped product including an inorganic fiber part of inorganic fibers that have a pyrolysis initiation temperature of 1900 C. or lower, and a surface layer of an inorganic substance for bonding the inorganic fibers to each other, and pressing the laminate at a temperature of 1000 to 1800 C. and a pressure of 5 to 50 MPa in an inert gas atmosphere; and a second pressing step of pressing a ceramic coated laminate obtained in the first pressing step at a temperature of 1600 to 1900 C., which is higher than that in the first pressing step, and at a pressure of 5 to 100 MPa in an inert gas atmosphere.

Provided is a method for producing an inorganic fiber-bonded ceramic material, which can produce, at a high yield, an inorganic fiber-bonded ceramic material with fewer defects, and with an end part and a central part equivalent to each other in microstructure and mechanical properties, and also makes it possible to increase the ceramic material in size. The method for producing an inorganic fiber-bonded ceramic material is characterized in that it includes: a first pressing step of setting, in a carbon die, a laminate to be surrounded by a ceramic powder, the laminate obtained by stacking a coated inorganic fiber shaped product including an inorganic fiber part of inorganic fibers that have a pyrolysis initiation temperature of 1900 C. or lower, and a surface layer of an inorganic substance for bonding the inorganic fibers to each other, and pressing the laminate at a temperature of 1000 to 1800 C. and a pressure of 5 to 50 MPa in an inert gas atmosphere; and a second pressing step of pressing a ceramic coated laminate obtained in the first pressing step at a temperature of 1600 to 1900 C., which is higher than that in the first pressing step, and at a pressure of 5 to 100 MPa in an inert gas atmosphere.

A silicon nitride substrate including silicon nitride crystal grains and a grain boundary phase and having a thermal conductivity of 50 W/m.Math.K or more, wherein, in a sectional structure of the silicon nitride substrate, a ratio (T2/T1) of a total length T2 of the grain boundary phase in a thickness direction with respect to a thickness T1 of the silicon nitride substrate is 0.01 to 0.30, and a variation from a dielectric strength mean value when measured by a four-terminal method in which electrodes are brought into contact with a front and a rear surfaces of the substrate is 20% or less. The dielectric strength mean value of the silicon nitride substrate can be 15 kV/rum or more. According to above structure, there can be obtained a silicon nitride substrate and a silicon nitride circuit board using the substrate in which variation in the dielectric strength is decreased.

The present invention provides a silicon nitride wear resistant member comprising a silicon nitride sintered compact containing -Si.sub.3N.sub.4 crystal grains as a main component, 2 to 4% by mass of a rare earth element in terms of oxide, 2 to 6% by mass of Al in terms of oxide, and 0.1 to 5% by mass of Hf in terms of oxide, wherein the silicon nitride sintered compact has rare earth-HfO compound crystals; in an arbitrary section, an area ratio of the rare earth-HfO compound crystals in a grain boundary phase per unit area of 30 m30 m is 5 to 50%; and variation of the area ratios of the rare earth-HfO compound crystals between the unit areas is 10% or less. Due to above structure, there can be provided a wear resistant member comprising the silicon nitride sintered compact having an excellent wear resistance and processability.

The present invention provides a silicon nitride wear resistant member comprising a silicon nitride sintered compact containing -Si.sub.3N.sub.4 crystal grains as a main component, 2 to 4% by mass of a rare earth element in terms of oxide, 2 to 6% by mass of Al in terms of oxide, and 0.1 to 5% by mass of Hf in terms of oxide, wherein the silicon nitride sintered compact has rare earth-HfO compound crystals; in an arbitrary section, an area ratio of the rare earth-HfO compound crystals in a grain boundary phase per unit area of 30 m30 m is 5 to 50%; and variation of the area ratios of the rare earth-HfO compound crystals between the unit areas is 10% or less. Due to above structure, there can be provided a wear resistant member comprising the silicon nitride sintered compact having an excellent wear resistance and processability.

A high temperature fastener including a bolt and a nut, where the bolt and the nut are constructed of an aluminum oxide ceramic material reinforced with silicon-carbide crystal whiskers or silicon nitride.

A nut plate (10) and a gang channel (78) are constructed of ceramic material. In one version, the nut plate (10) and gang channel (78) are constructed of aluminum oxide ceramic material reinforced with silicon-carbide crystal whiskers. In another version, the nut plate (10) and gang channel (78) are constructed of silicon-nitride. In a third version the nuts (54) are constructed of oxide ceramic material reinforced with silicon-carbide crystal whiskers or silicon-nitride and gage channel (78) are constructed of CMC (either oxide or non-oxide).

A silicon nitride substrate including silicon nitride crystal grains and a grain boundary phase and having a thermal conductivity of 50 W/m.Math.K or more, wherein, in a sectional structure of the silicon nitride substrate, a ratio (T2/T1) of a total length T2 of the grain boundary phase in a thickness direction with respect to a thickness T1 of the silicon nitride substrate is 0.01 to 0.30, and a variation from a dielectric strength mean value when measured by a four-terminal method in which electrodes are brought into contact with a front and a rear surfaces of the substrate is 20% or less. The dielectric strength mean value of the silicon nitride substrate can be 15 kV/mm or more. According to above structure, there can be obtained a silicon nitride substrate and a silicon nitride circuit board using the substrate in which variation in the dielectric strength is decreased.

A silicon nitride substrate including silicon nitride crystal grains and a grain boundary phase and having a thermal conductivity of 50 W/m.Math.K or more, wherein, in a sectional structure of the silicon nitride substrate, a ratio (T2/T1) of a total length T2 of the grain boundary phase in a thickness direction with respect to a thickness T1 of the silicon nitride substrate is 0.01 to 0.30, and a variation from a dielectric strength mean value when measured by a four-terminal method in which electrodes are brought into contact with a front and a rear surfaces of the substrate is 20% or less. The dielectric strength mean value of the silicon nitride substrate can be 15 kV/mm or more. According to above structure, there can be obtained a silicon nitride substrate and a silicon nitride circuit board using the substrate in which variation in the dielectric strength is decreased.

The invention proposed a novel hot pressing flowing sintering method to fabricate textured ceramics. The perfectly 2-dimensional textured Si3N4 ceramics (Lotgering orientation factor fL 0.9975) were fabricated by this method. During the initial sintering stage, the specimen flowed along the plane which is perpendicular to the hot pressing direction under pressure, through the controlling of the graphite die movement. The rod-like -Si3N4 nuclei was easily to texture during the flowing process, due to the small size of the -Si3N4 nuclei and the high porosity of the flowing specimen. After aligned, the -Si3N4 grains grew along the materials flowing direction with little constraint. textured Si3N4 ceramics fabricated by this invention also showed high aspect ratio. Compared to the conventional hot-forging technique which contained the sintering and forging processes, hot pressing flowing sintering proposed is simpler and lower cost to fabricate textured Si3N4.