Joining of silicon nitride ceramic composites with Y2O3–Al2O3–SiO2 mixtures

Hot-pressure sintered silicon nitride ceramic composites were joined to themselves using Y2O3–Al2O3–SiO2 mixtures. Reaction behavior at interface between Si3N4 and Y2O3–Al2O3–SiO2 mixtures during silicon nitride composite joining was studied by means of SEM, EPMA and XRD. The joint strength under different bonding conditions was measured by four-point bending tests. The results of EPMA and XRD analyses show that the liquid glass solders react with silicon nitride at interface, forming the Si3N4/Si2N2O/Y–Si–Al–O–N glass/Y–Si–Al–O glass gradient interface. From the results of four-point bending tests, it is known that with increasing joining temperature and holding time, the joint strength first increased, reaching a peak, and then decreased. The maximum joining strength of 315 MPa measured by the four-point bending test is achieved for the Si3N4 composite–Si3N4 composite joint bonded at 1823 K for 15 min. Destructed part is considered to start at the diffusion layer, indicating that the joining strength will be much higher than that value.