Joining of silicon nitride ceramics for high-temperature applications

A refractory silicon nitride joint, which contains beta-Si3N4 grains and gr ain boundary amorphous phase in the joined layer, was developed with the ai d of a ceramic adhesive based on the system Si3N4-Y2O3-SiO2-Al2O3. The simi larity in chemistry and microstructure between the parent ceramic and the j oint zone indicates that the joining mechanism is the same as that involved in the sintering of Si3N4. The resultant joint exhibits a high bond streng th of 550 MPa at 25 degrees C and retains a strength of 332 MPa at 1000 deg rees C. Post-joining hot-isostatic pressing was applied to strengthen the j oint, resulting in increased strengths of 668 MPa at room temperature and 4 64 MPa at 1000 degrees C.