Microstructure evolution of the Si3N4/Si3N4 joints brazed using Au-Ni-V filler alloys with different V content

Au-Ni-V filler alloys with different vanadium contents were designed to braze Si₃N₄ ceramic at 1373 K for 30 min, and the microstructures of brazing seams were investigated by SEM and TEM. When the Au-Ni-V filler alloy contains 5 at.% V, round-like NiSi, V, Au] precipitates form in the AuNi] solid solution matrix and a VN reaction layer with 0.5 μm thickness appears on Si₃N₄ interface. When the V content increases to 10 at.%, a new polygonal Ni₂SiV₃ phase occurs in the seam, and the NiSi, V, Au] precipitate coarsens and VN layer thickens. With increase of V contents to 15 and 20 at.%, laminar NiAu] and polygonal Ni₃V precipitates form. With 25 at.% V content in the filler alloy, the Ni₂SiV₃ and Ni₃V precipitates distribute homogenously in the brazing seam. These microstructure evolutions were attributed to the reaction between Si₃N₄ and vanadium, which forms VN reaction layer and releases Si into the molten alloy.