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 Ni[Si, V, Au] precipitates form in the Au[Ni] solid solution matrix and a VN reaction layer with 0.5 mu m thickness appears on Si3N4 interface. When the V content increases to 10 at.%, a new polygonal Ni2SiV3 phase occurs in the seam, and the Ni[Si, V, Au] precipitate coarsens and VN layer thickens. With increase of V contents to 15 and 20 at.%, laminar Ni[Au] 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. (C) 2011 Elsevier B.V. All rights reserved.