Microstructure and mechanical strength of Si3N4/Ni solid state bonded interfaces

Joining of hot pressed silicon nitride using Ni interlayers was done by diffusion bonding. Results were compared for two bonding temperatures: 1050 and 1150°C. For the lower joining temperature, no reaction was found but a limited diffusion of atomic Si into the Ni lattice was observed while for the higher temperature a thin reaction layer was found. Some nickel silicides and precipitates of a Y-rich phase were detected within this layer and an extensive diffusion zone of Si into Ni was measured. The mechanical properties of the joints were evaluated by shear and bend tests varying the thickness of the Ni interlayer. Bending strengths of 235 MPa were achieved at room temperature.