The friction stir welding tool member according to the present invention is made of a silicon nitride sintered body, wherein the silicon nitride sintered body contains 15% by mass or less of additive components except silicon nitride in such a manner that the additive components include at least one element selected from lanthanoid elements and at least one element selected from Mg, Ti, Hf, and Mo. In addition, it is preferable that the additive components further include at least one element selected from Al, Si, and C. According to the above-described configuration, a friction stir welding tool member having an excellent durability can be provided.

A method for manufacturing active metal-brazed a nitride ceramics substrate having excellent joining strength, includes: a step of preparing a mixed raw material; a step of forming a green sheet of the mixed raw material by a tape casting method; a step of removing a binder by performing degreasing; a step of performing sintering; a step of forming an aluminum nitride sintered substrate by performing gradual cooling; and a step of printing a conductive wiring pattern with active metal paste on the aluminum nitride sintered substrate.

In one aspect, ceramic bodies are described herein exhibiting composite architecture. Briefly, a composite ceramic body comprises a bulk region including a mixture of alpha-SiAlON and beta-SiAlON, and a surface region covering the bulk region, the surface region having a residual stress of −500 MPa to 500 MPa and a thickness of at least 5 μm.

Provided is a composite ceramic layered body, including: a substrate; and a composite ceramic that coats the substrate, the composite ceramic including a nitride phase and an oxide phase having an elastic modulus that differs from an elastic modulus of the nitride phase by 10% or more. The composite ceramic includes, among the nitride phase and the oxide phase, a first phase that occupies a largest area ratio, and a toughening phase that occupies an area ratio of 1% or more and has a largest difference in elastic modulus from an elastic modulus of the first phase. In a case in which the first phase is the nitride phase, the toughening phase is the oxide phase, and in a case in which the first phase is the oxide phase, the toughening phase is the nitride phase.

The present invention provides a welding tool member for friction stir welding comprising a silicon nitride sintered body, wherein the silicon nitride sintered body includes an additive component other than silicon nitride in a content of 15% by mass or less, and the additive component includes three or more elements selected from Y, Al, Mg, Si, Ti, Hf, Mo and C. It is preferable that the content of the additive component is 3% by mass or more and 12.5% by mass or less. It is also preferable that the additive component includes four or more elements selected from Y, Al, Mg, Si, Ti, Hf, Mo and C. Due to above structure, there can be provided a welding tool member for friction stir welding having a high durability.

A tape casting slurry composition for preparing a silicon nitride sintered body is provided. The tape casting slurry composition exhibits a viscosity suitable for tape casting, and thus, can easily control the area and thickness of the prepared green sheet, thereby preparing a large area silicon nitride sintered body having a thickness of a circuit board without post-processing processes such as grinding, and the like. Therefore, according to the present invention, a silicon nitride sintered body can be prepared using low cost raw materials by a simplified process, thereby securing efficiency and economic feasibility of the preparation process.

A sintered body includes a crystal grain containing silicon nitride, and a grain boundary phase. If dielectric losses of the sintered body are measured while applying an alternating voltage to the sintered body and continuously changing a frequency of the alternating voltage from 50 Hz to 1 MHz, an average value .sub.A of dielectric losses of the sintered body in a frequency band from 800 kHz to 1 MHz and an average value .sub.B of dielectric losses of the sintered body in a frequency band from 100 Hz to 200 Hz satisfy an expression |.sub.A.sub.B|0.1.

A method for producing a composite of cubic boron nitride dispersed in a SiAlON ceramic. This method involves mixing silicon nitride nanoparticles, aluminum nitride nanoparticles, silica nanoparticles, calcium oxide nanoparticles, and cubic boron nitride microparticles to produce a mixture. The cubic boron nitride may be coated with nickel. The mixture is sintered to produce the composite, and this sintering may involve spark plasma sintering and/or sintering at a relatively low temperature. The composite may comprise a mixture of Ca--SiAlON and -SiAlON ceramic reinforced by boron nitride in either or both cubic and hexagonal phases.

A method for producing a composite of cubic boron nitride dispersed in a SiAlON ceramic. This method involves mixing silicon nitride nanoparticles, aluminum nitride nanoparticles, silica nanoparticles, calcium oxide nanoparticles, and cubic boron nitride microparticles to produce a mixture. The cubic boron nitride may be coated with nickel. The mixture is sintered to produce the composite, and this sintering may involve spark plasma sintering and/or sintering at a relatively low temperature. The composite may comprise a mixture of Ca--SiAlON and -SiAlON ceramic reinforced by boron nitride in either or both cubic and hexagonal phases.

A method for manufacturing active metal-brazed a nitride ceramics substrate having excellent joining strength, includes: a step of preparing a mixed raw material; a step of forming a green sheet of the mixed raw material by a tape casting method; a step of removing a binder by performing degreasing; a step of performing sintering; a step of forming an aluminum nitride sintered substrate by performing gradual cooling; and a step of printing a conductive wiring pattern with active metal paste on the aluminum nitride sintered substrate.