Mechanical Properties of Joined Silicon Nitride

A technique is described to join Si3N4 ceramics using oxide glasses. The technique involves a glazing step, followed by a pressureless reaction treatment of 30 to 60 min at 1575° to 1650°C. Reactions between the glasses and Si3N4 are reported. Important events are dissolution of Si3N4 and the growth of Si2N2O crystals into the joint. The strength of joined bars depends on joint thickness. Two strength regimes are identified, and two corresponding fracture mechanisms are described. A maximum strength of ∼460 MPa is achieved for a joint thickness of ∼30 μm.