Joining of silicon nitride ceramics for high-temperature applications

A refractory silicon nitride joint, which contains β–Si₃N₄ grains and grain boundary amorphous phase in the joined layer, was developed with the aid of a ceramic adhesive based on the system Si₃N₄–Y₂O₃–SiO₂–Al₂O₃. The similarity in chemistry and microstructure between the parent ceramic and the joint zone indicates that the joining mechanism is the same as that involved in the sintering of Si₃N₄. The resultant joint exhibits a high bond strength of 550 MPa at 25 °C and retains a strength of 332 MPa at 1000 °C. Post-joining hot-isostatic pressing was applied to strengthen the joint, resulting in increased strengths of 668 MPa at room temperature and 464 MPa at 1000 °C.