Brazing of Si3N4 ceramic to copper

Silicon nitride is one of the most promising structural ceramics for high temperature applications. There is an increasing demand for joining this ceramic to metal structures. Direct brazing using an active filler metal has been found to be a reliable and simple technique, capable of producing strong and reliable joints. Several factors affecting the strength of such joints have been investigated and are reported in the literature. This preliminary study is directed mainly towards investigating the effect of the surface preparation of the base metal and of the load applied to the joint during brazing on the strength of brazed joints. Experiments were conducted for brazing silicon nitride to copper using a commercial Ag-Cu-Ti active filler metal with and without applied load. The Si3N4/Cu joint shear strength and sheer energy were determined for various brazing conditions. The initiation of the fracture was detected using acoustic emission sensing. The mechanism of bond formation is described, with emphasis placed on the active metal reaction with the joint materials. Both the interfacial adhesion and the microstructure were investigated. It was found that the smoother the surface finish of the copper base metal, the higher the joint shear strength attained. The sheer energy of the joints increased substantially as a result of applying a light load on the joints during brazing. (C) 1998 Elsevier Science S.A. All rights reserved.