Interfacial microstructure of the Si₃N₄/Si₃N₄ joint brazed with Cu-Pd-Ti filler alloy

Si₃N₄ ceramic was jointed with itself by active brazing with a Cu-Pd-Ti filler alloy. Interfacial microstructure of the Si₃N₄/Si₃N₄ joint was analyzed by EPMA, TEM and X-ray diffract meter. The results indicate that a TiN reaction layer with a thickness about 5 μm is formed at the interface between Si₃N₄ ceramic and filler alloy. The TiN reaction layer is composed of two zones: one next to the Si₃N₄ ceramic with grains of 100 nm and the other zone that connects with the filler alloy and has grains of 1 μm. The microstructure of the joint can be described as: Si₃N₄ ceramic/TiN layer with fine grains/TiN layer with coarsen grains/Cu[Pd] solid solution. Some new phases, such as Pd₂Si, PdTiSi, Ti₅Si₃ and TiN, were formed in the Cu[Pd] solid solution interlayer. With increasing brazing temperature from 1100 °C to 1200 °C, the thickness of the TiN reaction layer is not changed. Meanwhile, the amount and size of the TiN and Pd₂Si phases in the Cu[Pd] solid solution increase, while, the amount of the PdTiSi phase decreases.