Joining of silicon nitride with a titanium foil interlayer

This work focuses on various aspects of diffusion bonding of Ti-foil interlayer during the self-joining of Si3N4. Si3N4/Ti-foil/Si3N4 combinations were hot-pressed at temperatures ranging from 1200 to 1500 °C with different holding times and surface roughnesses. The microstructural characterization of the resulting interfaces was carried out by SEM, EPMA, and X-ray diffraction. Si3N4 could not be bonded to Ti at temperatures lower than 1400 °C. Successful joining occurred at higher temperatures by the formation of a reactive interface on the metal side of the joint. EPMA and X-ray diffraction confirmed the presence of Ti5Si3, TiSi, and TiN at the interface. Thicker interfaces were obtained for polished samples compared to those produced from as-ground samples and both interfaces grew in a parabolic fashion. Joint strength was obtained by four-point bending and a maximum joint strength of 147 MPa was achieved in samples hot-pressed at 1500 °C for 120 min. Joints produced at joining temperatures greater than 1450 °C gave an average bend strength of more than 100 MPa.