Interfacial reaction and joint strength of silicon nitride ceramic composites bonded with Y2O3-Al2O3-SiO2-Si3N4 mixture

Silicon nitride ceramic composite was joined to itself by heating an interlayer of Y2O3-Al2O3-SiO2-Si3N4 mixtures above their liquid temperatures in flowing nitrogen. The microstructure and chemistry of joints were characterised by SEM, EPMA and XRD, respectively. The results show that some elements of adhesive (Y, Al, O) diffuse into Si3N4 composite to form a diffusion layer. At 1600 C, the content of Si2N2O and beta-Si3N4 increases with an increase in holding time. When the bonding temperature is higher than 1600 C, the content of beta-Si3N4 increases. The joining strength of the joint depends on the interfacial reaction. The destructed part is considered to start at the diffusion layer, indicating that the joining strength will be much higher than that value. 19 refs.