Interfacial microstructure of Si3N4/Si3N4 brazing joint with Cu–Zn–Ti filler alloy

In this study, Si3N4 ceramic was jointed by a brazing technique with a Cu–Zn–Ti filler alloy. The interfacial microstructure between Si3N4 ceramic and filler alloy in the Si3N4/Si3N4 joint was observed and analyzed by using electron-probe microanalysis, X-ray diffraction and transmission electron microscopy. The results indicate that there are two reaction layers at the ceramic/filler interface in the joint, which was obtained by brazing at a temperature and holding time of 1223 K and 15 min, respectively. The layer nearby the Si3N4 ceramic is a TiN layer with an average grain size of 100 nm, and the layer nearby the filler alloy is a Ti5Si3Nx layer with an average grain size of 1–2 μm. Thickness of the TiN and Ti5Si3Nx layers is about 1 μm and 10 μm, respectively. The formation mechanism of the reaction layers was discussed. A model showing the microstructure from Si3N4 ceramic to filler alloy in the Si3N4/Si3N4 joint was provided as: Si3N4 ceramic/TiN reaction layer/Ti5Si3Nx reaction layer/Cu–Zn solution.