A novel sinter-bonding method for structural ceramics, having been developed by the authors, is applied to joining polycrystalline silicon-nitride (Si3N4) to itself. In the method, the source powder of 3Y-TZP/Al2O3 composites, which can show superplasticity , is used as an interlayer for the bonding. The temperature, stress and time to be applied for, and the thickness of the interlayer were variables for the bonding experiments. The bonded states were evaluated by SEM and SEM/EDX, and the strengths of the joints were measured by 4-point bending tests at temperatures from 300 to 1573K. The results obtained show many advantages such as that the joints possess greater heat resistance than those made by conventional bonding methods for ceramics using a metallic thin foil or an oxide solder as interlayer. The sinter-bonding process and bonding mechanism are discussed based on the SEM micrographs, EDX results and bending test results obtained in the present study. It appears that high mobility of the powder in the beginning stage of the bonding as well as superplastic flow of the sintered powder in the later stage make the contact of the Si3N4 to be bonded and the interlayer quite easy and consequently the diffusion bonding between them is facilitated.
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