Brazing Si3N4 Ceramic to Molybdenum Using an Ag-Cu-Ti Filler

A Si3N4 ceramic was successfully joined to molybdenum(Mo) using an Ag-Cu-Ti filler alloy. The interfacial microstructure of the Si3N4/Ag-Cu-Ti/Mo joint was investigated by scanning an electron microscopy, energy dispersive spectrometer, and x-ray diffraction. The results showed the joint brazed at 900˚C for 10 min was smooth, and there were no holes and cracks at the interface. A continuous reaction layer, which is composed of TiN and TiSi2, was formed near the Si3N4 ceramic, with TiN being located near the ceramic. The central part of the joint was composed of Ag- and Cu-based solid solutions. At the side near the Mo metal, there was a formation of the MoTi solid solution. The typical structure of the Si3N4/Mo joint was Si3N4/TiN  TiSi2 reaction layer/Ag(s,s) Cu(s,s)/MoTi/Mo. Because TiN and TiSi2 com-pounds are generated on the ceramic side, the microhardness of the reaction layer on the ceramic side was de-creased but still much higher than the hardness of the brazing seam and the Mo base material. The shear strength of the brazed joint was 204 MPa at room temperature.